Episode 196: Flu Shifts: Why Vaccines Still Matter

Chris Dall: Hello and welcome to the Osterholm Update, a podcast on Covid 19 and other infectious diseases with Doctor Michael Osterholm. Doctor Osterholm is an internationally recognized medical detective and director of the Center for Infectious Disease Research and Policy, or Cidrap, at the University of Minnesota. In this podcast, Doctor Osterholm draws on nearly 50 years of experience investigating infectious disease outbreaks to provide straight talk on the latest infectious disease and public health threats. I'm Chris Dall, reporter for Cidrap news, and I'm your host for these conversations. Welcome back, everyone, to another episode of the Osterholm Update podcast. The government shut down may be over, but the lack of CDC disease surveillance over that period means we are flying blind, so to speak. When it comes to Covid, flu and respiratory syncytial virus levels in the United States. Fortunately, our neighbors to the north have been keeping a close eye on respiratory viruses, and they've found something worth keeping an eye on. Earlier this month, a group of Canadian researchers published a review of early influenza data for the 2025 - 26  season that suggests that what appears to be emerging as the dominant substrain has acquired several mutations and doesn't match with the seasonal flu vaccine strain.

Chris Dall: That means the vaccine could be significantly less effective against the flu this year. The strain is already causing outbreaks in Canada, Japan and the United Kingdom. The team released its data early to encourage enhanced surveillance in the US. This is not the time to be flying blind into the respiratory virus season, the paper's author told Cidrap news. The mismatched flu strain and what it could mean for this flu season is among the topics we'll be addressing on this November 20th episode of The Osterholm Update. We'll also discuss Canada's loss of measles elimination status. Preview the Vaccine Integrity Project's upcoming review of the hepatitis B vaccine. Try to clarify the current picture for Covid 19 and other respiratory viruses. Provide an update on H5n1 avian flu and answer an ID query about infant botulism. And we'll bring you the latest installment of This Week in Public health history. But before we get started, as always, we'll begin with Doctor Osterholm's opening comments and dedication.

Dr. Osterholm: Thanks, Chris, and welcome back to everyone in the podcast family. It's good to be with you. As you know, we actually had a slightly longer break here between our podcast going three weeks instead of two weeks, as we're trying to time it around the Thanksgiving holiday so that we can make sure that we all have one right after Thanksgiving. And so, uh, we really appreciate the fact you're back with us after this period of time. I also want to just start out by saying, thank you, thank you, and thank you. We've talked about this idea that we are a family. As part of this podcast. We're now approaching our 200th episode. And for all of you who have been so faithful in staying with us and listening, providing feedback. I can't tell you how much that has meant to us. We feel it, and I really had a unique opportunity over the last month and a half with regard to my book tour that I did with my new book, The Big One. Having come out and to see so many of you at these book signings has been remarkable, and to hear your stories, and of course, to give me your opinion on the sunlight issue. Um, it has been a gift of gifts, and I can't say thank you in enough ways for all that you do to help us all feel as if we're together, even though we're somewhat separated by these microphone and earbuds that we use to listen to each episode.

Dr. Osterholm: So just thank you. I also just want to acknowledge we were very honored this past week to be listed as one of the Booklist Editor's Choice Picks for 2025, in the Health and medicine category for the book. And so for any of you who may have an interest in the book but haven't read it yet, I hope you do, and I hope you provide us your feedback. We really very much welcome that. Also, before I start, I want to just again acknowledge and thank our podcast crew. You know, Chris and I are obviously very publicly visible to you, but we have a whole team of individuals who work on this podcast who make me sound a heck of a lot smarter than I really am. And it just means so much to me to have this team. So today, I just want to take this moment to a special shout out to the podcast team for all they do to help make sure the information I provide is factual, it's timely, and most of all, it's information that hopefully you can use. So with that, let me move into the dedication portion of the podcast. Like all medications, they mean a great deal to me.

Dr. Osterholm: They're not just words. This one in particular, having so many of my friends and colleagues a part of this dedication, it means even more. We've recently dedicated episodes to federal workers who commitments to their agencies in the country has been questioned, as well as those who have endured politically motivated firings or reductions in forced layoffs. Many of these same workers recently faced yet another challenge being furloughed or required to work without pay during the longest government shutdown in our nation's history. According to the Bipartisan Policy Center, at least 670,000 federal employees were furloughed and roughly 730,000 were working without pay during the 43 day shutdown. The Department of Health and Human Services was not spared. Nearly 41% of the HHS workforce was furloughed, with CDC furloughing 64% of staff and NIH furloughing 75% of the staff. Remember that CDC had already issued over 1000 layoff notices during the shutdown, although some have been rescinded. But nonetheless, combined with the furloughing situation, it added to the challenge of trying to do the business of public health for the government workers who have jobs to return to. I imagine there's a great deal of relief to get back to their work and regular paychecks. But once again, we've seen this job security shaken, and the conditions of their work made undeniably more difficult. On a professional level,

Dr. Osterholm: these agencies are being asked to do more with much less. And that limits their ability to continue providing services and performing essential duties. For CDC, that means interruptions in laboratory testing, outbreak reporting and the publication of clinical guidelines. According to the recent joint statement from the heads of four infectious disease associations, these interruptions are already being felt by clinicians and public health practitioners with direct impacts to the quality and availability of patient care. And on a personal level, let us imagine how a month of missed pay or a layoff notice impacts a family and the people who depend on them. It's the rent or mortgage payments. You suddenly can't make. The prescriptions you now have to stretch out or the child care bill you can't cover. And for those working without pay. It's a unique strain of having to get up each morning, show up professionally, and perform at full capacity while wondering how will you afford gas to drive home. These stretches blur the line between professional identity and personal vulnerability. They leave workers wondering whether the institutions they serve can still protect them, even as they continue protecting the public from the threat. Seen and unseen, a shutdown may be a political standoff in Washington, D.C., but to these workers, it's very, very personal. We're dedicating this episode to the federal government workers who were furloughed or who worked without pay during the shutdown to their resilience, their professionalism, and their unwavering dedication to service, even when the dedication is not returned.

Dr. Osterholm: We recognize their contributions and hope that the systems that depend on them finally offer the stability and respect they deserve. Now, let's move on to that lighter part of the podcast. Although I must acknowledge her in Minnesota right now, the light is a little bit short from what we need. Uh, today in Minneapolis, uh, sunrise is at 7:17 a.m., sunset at 4:39. That's nine hours, 21 minutes and 31 seconds of sunlight. We're getting down there to the very, very minimum sunlight here in the Twin Cities. In fact, on December 5th, just a few weeks off, the sun will actually set here at 4:31, the earliest. It sets throughout the entire year. So we're only literally just eight minutes away from that darkest afternoon. Now, I'm happy to report in Auckland at the accidental Belgian Beer House on Vulcan Lane. And to all of our dear friends there, your sunrise today was at 5:59 a.m., your sunset at 8:13. That's 14 hours, 13 minutes and 50 seconds of sunlight. You are still gaining sunlight at one minute and 38 seconds a day. Wow, it's going to keep getting brighter. Please share some of that sunlight with us.

Chris Dall: Mike, let's start with the mismatched flu strain. Now, our listeners should know that this answer might get into some very technical detail, but what is your takeaway from the Canadian paper and from the data we now have in Canada, UK and Japan? And to take it down to a very basic level, do we know enough to say whether the flu shot that I just got this past weekend is going to be less effective?

Dr. Osterholm: Yes, Chris, this can get very technical, but I'm going to do my very, very best to break it down and make it digestible. I think it's best to start with the basics of influenza virus itself. There are three types of influenza virus that infect humans influenza A, B, and C. Although influenza C infections are not common and influenza pandemics have only been caused by influenza A. For the purpose of this specific answer, we're really only going to be looking at influenza A. Now, if you can imagine the cartoon image of a virus or the image that has been circulated of the Covid 19 virus. You'll picture a round center or core with proteins protruding from the round center, almost as if they're the tops of a vegetable growing in a garden. In the case of influenza, those proteins are called hemagglutinin Ha and neuraminidase Na, which act as what we call antigens, and they can trigger an immune response once recognized by your immune system. There are 18 Ha subtypes, referred to as H1 through H18, and there are 11 neuraminidase subtypes referred to as N1 through N11. Influenza A is categorized into what we call subtypes, based on which Ha and Na are present, which is how we get strains such as H1n1, H5n1, or H3n2. From there, the subtypes are further categorized into clades and subclades based on genetic similarities of their Ha.

Dr. Osterholm: Influenza is notorious for being highly variable and also unpredictable. The virus changes in two ways: antigenic drift and antigenic shift. Antigenic drift refers to the very small changes or mutations that result in changes to the surface proteins, or the Ha or the Na. Drift is much more common than shift, and is the reason we need to update our flu vaccines from year to year. Antigenic shift, on the other hand, is the major change that results in a new combination of Ha and Na proteins. Shift can occur when there are changes to an animal strain that allow it to jump into humans, and also through a process called reassortment. When a cell is infected with two different flu viruses, and those viruses that cell swap genetic material and create a brand new virus. Antigenic shift is much more concerning because it can lead to pandemics. Now, I know that is technical, but I promise I'm getting to the point here, Chris. Twice a year, the W.H.O. reviews global flu surveillance data and makes recommendations on strains to include in the upcoming seasonal vaccines, and countries then decide if they want to accept that recommendation or make changes. This happens in February for the northern hemisphere vaccines and in September for the Southern hemisphere vaccines.

Dr. Osterholm: If this sounds like a flawed system, you're right. Our current vaccines take so long to manufacture that we have to pick virus strains six months in advance, knowing what we're dealing with with a highly variable virus. It emphasizes the need to invest and improve vaccines that don't target variable parts of the highly variable virus, an issue that we're working on at Cidrap with our Influenza Vaccine Research and Development roadmap. We will link to that roadmap in the show. Notes. In February, H1n1 was the predominant strain in the Southern hemisphere, and H3n2 subclade J was circulating as well. Because of this, the recommendations for the 2025 - 2026 vaccines for the Northern Hemisphere were based on these strains circulating back in February of 2025. However, what the Canadian research team that you noted found is that the H3n2 subclade J strain of influenza that was circulating, especially on the back end of the southern hemisphere of 2025 season, shifted from subclade J to subclade K over the summer. There are several important things that this means for us. First, and do I say. Fortunately, Doctor Danuta Stravinsky, the senior author of the Canadian paper, as well as the epidemiology lead for Influenza and Emerging respiratory Pathogens at the British Columbia Center for Disease Control, told our Cidrap news reporter Stephanie Sucher this week that this is a major drift, not a shift.

Dr. Osterholm: So while it's too early to know exactly what it means for the Northern Hemisphere's flu season and specifically the US, there is no reason to believe that this will cause an influenza pandemic. It also means that since we've had H3n2 subtypes circulating for decades, our antiviral drugs should not be affected. Unfortunately, the second takeaway is that due to the timing of this major antigenic drift, which occurred in the tail end of the Southern Hemisphere season, our seasonal vaccines already had been finalized to include a subclade J of H3n2, not subclade K. Early data from the United Kingdom and Japan, which have reported early and severe starts of their flu seasons, show that this H3n2 subclade K strain, accounts for 90% of the flu samples thus far this season. One point that is not often mentioned when discussing the severity of influenza in these other countries is the fact that virtually all of them are reporting some of the lowest levels of influenza vaccination in the population that they've seen for many years prior to a flu season. So I think that, too has to be taken into account as a possible reason for why we're seeing more severe illness in these countries. Although our season here in the US has had an uncharacteristically slow start, H3n2 does currently account for more than 70% of the US cases, making it the dominant strain here as well.

Dr. Osterholm: If this strain continues to spread across the US and be dominant, our vaccine will in fact be somewhat of a mismatch. Historically, compared to H1n1 dominant seasons, H3n2 dominant seasons have caused more severe illness, especially in older adults as well as lower vaccine efficacy. All that is to say, with potentially mismatched vaccine in H3n2 dominant season, we could be in for a rougher season than we might otherwise have. I want to emphasize, though, that even though the vaccine could be a mismatch, that does not mean it's not important and can save lives. It can still provide some very important protection. A preprint published this past week out of the United Kingdom showed that the vaccine is still currently 70 to 75% effective in reducing Hospitalizations and kids, and 30 to 40% effective at reducing hospitalizations in adults. I'll gladly take that over. No protection at all. Sure, it is early in the season before there have been any waning of effectiveness, but this is still a promising sign and a clear reason to seek out a flu vaccine if you have already not done so. We'll keep you posted on this in the weeks ahead.

Chris Dall: We're going to stay in Canada here for a moment, because last week, the Pan American Health Organization announced that the country had lost its measles elimination status, which it has had since 1999. Practically speaking, Mike, what does this mean? And could this be where the US is headed if it continues on its current trajectory? 

Dr. Osterholm: Yes. This development represents a real setback in our fight against measles, one of the world's most infectious diseases. Canada has seen one full year of transmission, which began in New Brunswick in October 2024 before taking hold in Ontario and Alberta, leading to more than 5100 cases in ten provinces. Although declining overall, measles was still spreading in Alberta, British Columbia, Manitoba and Saskatchewan. Tragically, two preterm babies died after being infected before birth. This was heartbreaking, and it should be noted that maternal child transmission of measles during pregnancy is a relatively new phenomenon. Previously, most women of childbearing age were either immune due to being infected at a young age before vaccines were available, or immune due to vaccination. As vaccination rates in pregnant people continue to decline, we can expect to see cases like this more often. In addition to sustaining transmission with the same viral strain, particularly with the drop in vaccination rates, can lead to the loss of measles elimination status, according to Paho. It's important to note for a loss of measles elimination status, two things have to happen. One is the virus that originally started the first outbreak must still be found at least 12 months later, circulating in the community. This means that you need to have viral isolates that you can test genetically, to be certain that that's what you're seeing. In some instances, there may be a more commonly found measles virus strain that is not always clear. Is this ongoing transmission from that original outbreak, or is it just a series of simultaneous introductions occurring but with the same virus? That's why the epidemiologic data becomes important in terms of understanding.

Dr. Osterholm: Are there links that demonstrate that the case is occurring 12 months later, actually can be traced back outbreak by outbreak, back to that original introduction of the virus one year before with Canada's loss of measles elimination status. Paho's American regions also lost that designation by default. In the Americas, which includes the US, measles cases are 30 fold higher this year than in 2024. Canada must now go one year without measles transmission from the current outbreak strain to regain elimination status. The Public Health Agency of Canada said last week it will focus on improving measles vaccine uptake, which has been complicated by physician shortages, regional differences in healthcare and decreased public health funding and outreach to religious and rural communities in the country. Since the large West Texas measles outbreak began in January, the US has recorded 1723 confirmed cases in 45 outbreaks in 43 jurisdictions, the highest measles activity since measles was eliminated in 2000. For comparison, last year the US reported 285 cases. On Monday, in a phone call with state health departments, the CDC linked the Texas outbreak to the current one in Utah and Arizona by looking at the genetic makeup of the viruses found in each one. It is still unclear if there is epidemiologic data supporting the fact that the Texas outbreak strain continued to be transmitted in different regions of the country, and now still circulating in such a way as to have been transmitted for at least a year. This telephone call was reported on Tuesday morning by The New York Times, and it also quoted experts in the article as saying the possibility of losing our measles elimination status is deeply embarrassing for a high-income country with a wealth of medical resources, so we have lots of work to do.

Dr. Osterholm: This virus is still spreading, with 42 cases reported just last week and current hotspots along the Utah-Arizona border and in upstate South Carolina. Of all the measles patients, 92% have been unvaccinated or didn't know their vaccination status. Only 4% had received both recommended doses. But there is hope in Minnesota. Wastewater surveillance is showing promise for its ability to detect even the smallest presence of virus in sewage from homes and buildings. As you may remember, this technique for early disease surveillance emerged during the Covid 19 pandemic. This fall, molecular testing of wastewater in Rochester, Minnesota, detected viral traces during a measles outbreak that infected three people in that city, pushing the state's total cases to 24 this year. Amazingly, a viral levels in Rochester's wastewater, which could be detected, rose at the same time as an unvaccinated child who had traveled abroad tested positive for measles at the Mayo Clinic. Levels climbed again when two relatives of the child also contracted measles. The Rochester test case was the final step before the Minnesota Department of Health starts publicly reporting levels of measles virus in wastewater, which can help signal outbreaks and give public health officials time to marshal resources and communicate the risk with clinicians in the public. This technique, along with increased vaccine coverage and education, can hopefully help us make progress against this potentially deadly disease.

Chris Dall: So, Mike, just to clarify, on measles elimination, if the CDC in January 2026 finds epidemiologic data suggesting that the outbreak strain that started in January 2025, in West Texas is still going in the US. Is that 12 months of straight transmission?

Dr. Osterholm: That would be, in fact, 12 months of straight transmission, with documentation, epidemiologically, that they could trace the virus from one outbreak to another to another, to another. It also, of course, has the genetic component to it where it is a fingerprint virus. So it's the same one. And so in fact, that would be the information that would determine our measles elimination status.

Chris Dall: Let's turn now to some vaccine news. Late last week, the CDC posted a notice in the Federal Register that the next meeting of the Advisory Committee on Immunization Practices will be December 4th and 5th. Among the topics they'll be discussing and voting on is whether all children should receive a birth dose of the hepatitis B vaccine, a question they discussed at the last meeting but did not vote on in anticipation of that meeting. Cidrap Vaccine Integrity Project has now said it's going to conduct a review of evidence supporting the universal birth dose. Mike, what else can you tell our audience about this effort?

Dr. Osterholm: Chris, I'm very excited to share what the Vaccine Integrity Project has been doing in anticipation of the ACIP's vote on the birth dose of hepatitis B vaccine. But first, I want to take a step back and explain why we're doing this. Hepatitis B virus infection targets the liver, and it can be spread through contact with infected blood or body fluids. Infants can become infected through maternal fetal transmission during pregnancy, labor and delivery, and though it is rare, postnatal transmission to infants can also occur later in life. Hepatitis B infection is typically associated with sexual transmission or shared needle use. Infants who develop hepatitis B infections typically have a much more aggressive clinical course than those who are infected as adults. 90% of perinatal infected infants will go on to develop chronic hepatitis B infection, and 25% of those individuals will die prematurely due to chronic liver disease complications related to hepatitis B infection, including cirrhosis and hepatocellular carcinoma, the most common form of liver cancer. Fortunately, we have a very safe and effective vaccine that protects infants against hepatitis B that is currently routinely administered within 24 hours of birth. This vaccine has saved lives and reduced morbidity caused by complications from chronic infection. It is a public health success that should be celebrated. Sadly, this vaccine, and particularly the routine administration of a birth dose, has come under fire by many leaders in the anti-vaccine movement, including RFK Jr and members of the current ACIP committee.

Dr. Osterholm: As a reminder to listeners, the current ACIP committee includes only individuals appointed by Secretary Kennedy, as he fired all the other committee members back in June. The ACIP is now largely made up of individuals with little or no training in public health, vaccinology or other related fields, and many of them are outspoken anti-vaxxers. The message circulated from many of these individuals is this birth dose is unnecessary for most infants. They argue that since hepatitis B testing is a routine part of prenatal care, infants who are born to mothers that test negative for hepatitis B have no reason to receive the vaccine. This can be a convincing argument to those who are not informed on the nuances of the issue, but it's important to consider four groups who would be left behind if we only administered vaccines to individuals who tested positive. First, all individuals who are infected but have missing test results or were not tested during pregnancy. Second, those with false negative test results. Although this is rare, we have to acknowledge that our medical tests aren't perfect and some amount of false negative results are a reality. Third, those women who become infected after their prenatal screening but before labor and delivery. And fourth, infants who are infected through postnatal exposure. Removing the birth dose recommendation will leave all of these groups unprotected.

Dr. Osterholm: You may be wondering why we bother to test during pregnancy to begin with, if a birth dose is administered, regardless of the results. The purpose of the test is not to rule out the necessity of a vaccination, but to determine if additional steps need to be taken to prevent hepatitis B infection, specifically administering the vaccine within 12 hours, rather than the standard 24 hours after birth, and the additional administration of hepatitis B immune globulin. All that is to say that universal birth doses of hepatitis B vaccine are an evidence-based public health measure, even in the case of a negative test during prenatal screening. We won't get into detail about our preliminary results because we'll share more once the report is up on the website. But I'll say this, the vaccine is safe and effective, and nothing we have found so far suggests the need for any change in our current vaccine recommendations on the administration of a birth dose. We hope to share the report in early December, just before the ACIP meets to vote on this issue. The vote on removing the hepatitis B birth dose recommendation is just another attempt this administration is making at dismantling the public health systems that have kept us safe for decades, and I can only hope that the ACIP sees the value in this vaccine and votes accordingly.

Chris Dall: As I noted in the intro, Mike, we've been flying blind during the government shutdown when it comes to Covid, flu, and RSV data. Fortunately, the CDC is now back. The shutdown is over. Even more fortunately, we've had people like Caitlin Rivers and her team trying to provide some insight into what's going on. What are they seeing?

Dr. Osterholm: Chris, the CDC is starting to post some of the data, but these respiratory viruses are still looking pretty fuzzy. Overall, what I can tell you is that Covid activity is still very low and not showing any signs that we need to be concerned about right now. While flu and RSV activity are low, they are starting to increase. Let me dive a little deeper into the details. Starting first with influenza. Despite the concerns about H3n2 subclade K that I talked about earlier and the concerning high activity in other countries around the globe. There is still not a lot of influenza activity at the moment, but I have no doubt it will be here soon. Test positivity has doubled over the past week from 1 to 2%, and I expect the number to continue to rise. Flu activity is considered minimal in 48 states and the District of Columbia. Low in Louisiana and Oklahoma has insufficient data. These levels are measured by outpatient respiratory illness visits, which is one of the primary metrics we use to monitor influenza activity. It is the percentage of doctor's office visits for influenza like illness, which is a fever, plus a cough and or sore throat. When this percentage goes above the national baseline of 3.1%, influenza activity is considered elevated and we do not declare the end of a flu season until we're back below that threshold.

Dr. Osterholm: We are currently well below that threshold with 2.1% of visits for influenza like illness. While the overall percentage of visits for influenza like illness is below the national threshold, that is not the case for all age groups. 6.9% of outpatient visits in the 0 to 4 year old age group, and 3.5% of visits in the 5 to 24 year old age groups are now for influenza like illness. Let me just add, also, as a very sobering note, we now have updated numbers for the number of deaths in children with influenza last year in the 24 - 25 season. We now have documented 287 children, half of which had no risk factors for severe influenza died as a result of their infection. 287. That is, only one less than died in 2009, in that influenza pandemic. So it's just a reminder of what influenza can do. Now shifting over to RSV, where data are more limited. What we know is that the activity is low but slightly increasing over the past week. Test positivity has increased from 1.1 to 1.4%, and emergency room visits for RSV are also increased and remain highest in children under age five. Finally, shifting over to Covid, where activity is low and decreasing, which seems unusual compared to previous years. But it just goes to show, as I've said time and time again, Covid 19 is not a seasonal disease in the sense we see influenza and RSV, but rather we call it seasonal because it happens in every season.

Dr. Osterholm: We have yet to get a wastewater update from CDC on Covid activity, but are expecting one tomorrow. So we look forward to having that to share with you all in the next episode. Emergency department visits for Covid are also very low, with 0.3% of Ed visits being diagnosed with Covid 19, which is as low as we've seen over the past year and down from the peak of 1.7% in August. Unfortunately, we still do not have updated weekly death data or updated variant tracking data, but we will be sure to share these with you as soon as we have them. As we head into the holiday season, I urge all of you to get your vaccines if you have not done so already. It is not too late to protect yourself and your loved ones particularly. We're talking now about your parents, your grandparents, your children, your grandchildren. Now is the time. Activity may be quiet right now, relatively speaking, but please, no respiratory season is coming and we surely could have a challenging flu season based on what we've seen in other countries. Now is the time to get your vaccine.

Chris Dall: We're going to come back to flu here now, but it's bird flu. We continue to get reports of H5n1 outbreaks in commercial poultry and wild birds here in the US. But there's a new paper that's getting a lot of coverage on the devastating impact that the virus has had on elephant seals on a remote island in the South Atlantic. Mike, is this just an example of how deadly this virus can be in mammals?

Dr. Osterholm: Well, Chris, it surely is an eye-catching report when you're talking about unusually high mortality involving thousands of magnificent elephant seals in one of the most remote corners of the planet. It's something you pay attention to. And that's really what this paper documents on the South Georgia island in the South Atlantic Ocean, roughly halfway between the southern tip of South America and Antarctica. For context, this is a place that's 800 miles from the nearest continent, with no permanent human settlements. Yet the virus, H5n1 still made it there, likely for migratory birds. This is a lesson about how far and wide these bugs can travel. Unfortunately, when the virus arrived in 2023, it ended up transmitting to these elephant seals and initially, some were dying. Over time, however, the researchers that have been documenting these populations, which happens to include the world's largest breeding colony of female southern elephant seals noticed a substantial decline in the number of animals observed in 2024 compared to the previous years, which included almost half of the breeding females. An estimated total loss of more than 50,000 animals. Now, it's hard to know what portion of these losses could be specifically attributed to H5n1, but the variation compared to past years was so far outside the norm, it's very likely the virus played a major role. Of course, one factor that certainly doesn't help limit transmission is the ecology of these seals.

Dr. Osterholm: During the breeding season, they congregate in large, dense colonies with lots of close contact. So once the virus enters the population, which is readily susceptible, it has every opportunity to take off. However, in terms of understanding how deadly this virus can be in mammals, it's hard to really say exactly what this means. Clearly, in this species, under these conditions, H5n1 is highly deadly, and it's important to understand that. But it's also important to note that this isn't a universal pattern that plays out across all mammals. In fact, severity appears to vary quite a lot by species. As an example, consider the cases in the past year in dairy cattle that happened right here in the US. Most of those were mild or even subclinical infections. There are exceptions, of course, but broadly speaking, the picture with cattle looks nothing like what we're seeing with elephant seals. Why is that the case? Well, the truth is we don't really fully understand why we can get a general sense looking at host characteristics, including things like receptor sites in certain tissues. Understanding the route of exposure, the dose, the pathogenesis, the virus, etc. but there's not an equation where we can determine the severity by adding a plus b plus c. So we have a lot more to learn. Unfortunately, the ongoing spread of this virus is providing some very hard earned lessons, particularly for certain mammal species.

Chris Dall: Now it's time for our ID query. This week, we've gotten a lot of questions about an outbreak of infant botulism in the US that's tied to contaminated powdered infant formula. Mike, what can you tell our listeners about this outbreak? Well, first.

Dr. Osterholm: I'd like to thank our listeners who asked about this very important issue. Infant botulism is very different from other types of botulism, such as foodborne botulism that can make adults sick after ingesting food contaminated with the botulinum toxin. I might add this toxin is one of the most poisonous chemicals to humans that we know. Infant botulism occurs when infants ingest spores of Clostridium botulinum bacteria. Because infants don't have a mature gut microbiome, the bacteria can actually grow and produce botulism toxin within their intestines. In contrast, adult botulism generally occurs when ingesting a toxin produced by Clostridium botulinum, which can form in an improperly stored or preserved food, not just from the ingestion of spores themselves. This is why it's recommended that individuals under one year of age do not consume honey. It can contain C botulinum spores that can make infants sick. But since it does not contain botulinum toxin itself, it does not pose a risk to those with mature gut microbiomes. Constipation is generally the first sign in infants, but this can quickly progress to neurological signs and respiratory distress. The consequences of infant botulism are so severe that treatment is usually started right away if a clinician suspects the diagnosis. Instead of waiting for laboratory confirmation, the treatment for infant botulism what we call baby capital B, capital I, capital G, which stands for baby botulism immune globulin and it contains antibodies that can neutralize the toxin, which are delivered intravenously. The current outbreak has linked infant botulism to byheart whole nutrition infant formula. This includes both the formula cans as well as the single serve packets. There have been 23 cases in infants so far, all of which have required hospitalization, according to CDC's latest update on November 14th.

Dr. Osterholm: The outbreak spans 13 states and includes Minnesota. Thankfully, no deaths have yet been reported, and we're crossing our fingers and hope that it remains that way. Importantly, the FDA does not have the same regulatory authority over infant formula as it does other food products in regards to issuing recalls. FDA can recommend the recall of formula product, but the formula company has to issue a voluntary recall themselves initially ByHeart only agreed to initiate a voluntary recall of two specific lots of formula that were reported to have been consumed by infected infants. However, FDA requested an expansion of the voluntary recall to all byheart infant formula on the market and as of November 11th. Finally, byheart, complied with FDA's recommendations and has voluntarily recalled all infant formula products. It's important for parents to be aware of infant botulism risks, even if their child does not consume byheart. Formula. Most infant botulism cases in the United States are thought to be acquired from inhaling C botulinum spores from the natural environment, such as soil or dust particles. However, some food sources, particularly honey, are known to be frequently contaminated with Clostridium botulinum spores, which are in the environment and that can cause illness. In 2018, there was an infant botulism outbreak in Texas linked to honey filled pacifiers purchased in Mexico or online where four infants were hospitalized. I hope the recall of the byheart products, as well as the media coverage that aims to reach those who have already purchased the product and may be using it at home, will be sufficient to stop the outbreak soon. We promise to keep you updated on the current outbreak as more information becomes available.

Chris Dall: Now it's time for this week in public health history. Mike, what are we commemorating today?

Dr. Osterholm: Well, we actually have a unique public health history segment today where instead of featuring an individual or notable event, we'll highlight a critical sector of public health. In the United States and across the globe, rural and remote areas face a unique set of constraints and challenges to their population health. Rural areas also contain unique strengths, with many generational family relationships and collective understanding of community needs. However, the field of rural health did not emerge as a defined area of focus until the 20th century, with a central hub in North Carolina. In 1912 Robeson County was established as the first official rural health department in the United States, while the State Board of Health for North Carolina was established 35 years prior. Robeson County leaders like Dr. B.W. Paige saw the unique needs of the rural populations and sought to mitigate special sanitation threats like hookworm and typhoid. In Doctor Paige's first year, he examined 45 schools, vaccinated 525 children, and inspected more than 500 rural homes. This early investment was vital, but it wasn't until 1973 when Jim Bernstein, another public health leader in North Carolina, would found a first of its kind State Office of Rural Health, a former Public Health Service officer with experience in both the Peace Corps and Indian Health Service, knew the importance of health care access for those in resource limited settings. He was committed to ensuring everyone in rural areas of North Carolina had access to primary care, and piloted a model that expanded licensure for nurse practitioners and physician assistants to meet these needs so communities had stable access to a provider even when a full time physician was not available. He helped to launch a model of community run rural health centers, which eventually took off in all 50 states. Today, November 20th, is National Rural Health Day. While rural communities continue to face significant challenges, including hospital closures and reduction in essential services. I want to extend my gratitude to the clinicians, public health professionals and community leaders who work tirelessly to ensure that every person, no matter where they live, have access to the care and resources they need to live a healthy life.

Chris Dall: Mike, what are your take home messages for today?

Dr. Osterholm: Well, first of all, I just want to reemphasize that the seasonal virus activity is still very low overall, but I do think that influenza is on its way up and RSV may not be far behind. Now is the time to get vaccinated. And remember, if you're thinking about vaccinating your children, remember 287 children died last year from flu in this country. Half who had no identified risk factor for flu. So it wasn't that somehow you could have anticipated they needed to get vaccination. I surely would encourage all the grandparents and parents out there to help those children get vaccinated. And of course, for those who are older, who are immunocompromised again. Uh, the influenza and Covid vaccines both can do a great deal to reduce your likelihood of ever experiencing a hospitalization as a result of your infection. Number two, the flu strains have changed, just as I noted. But at this point, we have every reason to believe that the vaccines will still perform fairly well. We will keep you up to date on that as we see more activity in our community. And finally, the infant botulism outbreak is an example of what public health does every day to save lives by uncovering these cases, determining the pattern of activity in the community, and quickly reacting to getting a product off the market saves lives. It makes the world a safer place for all of us. Thank you, Public Health, for what you did together with the clinicians who are so involved with the care of these children to identify the source of this infant botulism illness and to put an end to it.

Chris Dall: And what have you selected for a closing song today, Mike?

Dr. Osterholm: Well, I think it's fair to say that we all recognize these are very difficult times in our country, for that matter, around the world looking for something that is a bit more uplifting, or at least surely showing how we all can be together. Just like I keep talking about with this podcast family, we picked a song from Billy Bragg, a longtime English singer, songwriter, author and political activist, and this is a song from his 12th studio album. The title of the album is Mr. Love and Justice. It was issued in March of 2008. The song is "I keep faith". If you want to make the weather, then you have to take the blame. If sometimes dark clouds fill the sky and it starts to rain, folks complain. And though your head may tell you to run and hide. Listen to your heart and you'll find me right by your side. Because I keep faith, I keep faith, I keep faith, I keep faith in you, yes, I do, I keep faith in you. If you think you have the answer, don't be surprised if what you say is met with anger, contempt and lies. No matter how hard you may want to just walk away, reach out. You'll find me there beside you all the way. Because all the dreams we shared I never knew no one who cared about things. The way I've seen you. It doesn't matter if this all falls off the cliff together. We are going to see it through. I know it takes a mess of courage to go against the grain. You have to make great sacrifices for such little gain and so much pain.

Dr. Osterholm: And if your plans come out to nothing washed out in the rain, let me rekindle all your hopes and help you start again. Because I keep faith in you, yes I do, I keep faith in you. I keep faith in you, Billy Bragg "I keep faith". Thank you all very much for joining us again this week. It's good to be back with you. I missed you, and, uh, we welcome your feedback. Thank you to all those that send us cards and letters. We read every one of them. Uh, it's often the most enjoyable part of my day is to read the feedback from all of you, uh, understanding what this podcast means to you and also understanding how we can improve it. We're always open for that. I want to again, thank the podcast crew. Thank you. Chris. Uh, isn't he wonderful? He keeps me on the straight and narrow and keeps me focused. Uh, remarkable. And I just also want to say, as we come into this holiday season, you know, it can be tough sometimes in the holiday season. It's one where it should be all full of cheer and joy. But it also can be challenging. And we're going to be here for the next few weeks with you. And we promise to do what we can to help make this an enjoyable holiday season for you. So thanks again. Be kind out there once a day. Do something kind. Just do it. You'll find out how much it really means to everyone. And be safe. Get those vaccine doses. And thank you so, so much.

Chris Dall: Thanks for listening to the latest episode of the Osterholm Update. If you enjoyed the podcast, please subscribe, rate and review wherever you get your podcasts, and be sure to keep up with the latest infectious disease news by visiting our website CIDRAP.umn.edu. This podcast is supported in part by you, our listeners. If you would like to donate, please go to CIDRAP.umn.edu/support. The Osterholm Update is produced by Sydney Redepenning and Elise Holmes. Our researchers are Cory Anderson, Meredith Arpey, Leah Moat, Emily Smith, Clare Stoddart, Angela Ulrich, and Mary Van Beusekom.