ACIP targets up to 159 million Americans for H1N1 vaccination

Jul 29, 2009 (CIDRAP News) – The top US advisory panel on immunizations recommended today that groups totaling up to 159 million people be targeted for vaccination against the pandemic H1N1 influenza virus but that a narrower population of about 41 million have priority if initial supplies are short.

The Advisory Committee on Immunization Practices (ACIP) picked five target groups for initial immunization because of their increased risk of H1N1 infection or complications or their contact with vulnerable people:

  • Pregnant women
  • Household contacts of babies under 6 months of age
  • Healthcare and emergency medical services (EMS) workers
  • Children and young people aged 6 months through 24 years
  • People between 25 and 64 years who have chronic medical conditions

But if the demand for vaccine outstrips supplies, said Dr.Anne Schuchat of the Centers for Disease Control and Prevention (CDC), the five groups would be as follows:

  • Pregnant women
  • Healthcare and EMS workers who have direct contact with patients or infectious substances
  • Household contacts of babies younger than 6 months
  • Children aged 6 months through 4 years
  • Children and adolescents from 5 through 18 years who have risk factors for flu complications

Healthy people between the ages of 25 and 64 can be immunized after the demand from the target groups has been met, said the committee, which advises the CDC. Because people 65 and older seem to have a lower risk of H1N1 infection than younger people, they can be vaccinated as supplies permit and other groups are served, the panel advised.

"The H1N1 outbreak so far has to large extent spared that [elderly] population . . . so the idea was that if supply is adequate and global circumstances permit, vaccine could be offered at that time, said Schuchat, director of the CDC's National Center for Immunization and Respiratory Diseases.

Speaking at a press conference after today's ACIP meeting, Schuchat said the broader target groups total roughly 159 million people, adding, "But there's a lot of overlap in some of the groups, so it's probably lower than that."

Schuchat said the smaller set of target groups, or what she called the "just-in-case prioritization group," numbers about 41 million people.

The committee issued its recommendations as five vaccine manufacturers race to make H1N1 vaccines ordered by the Department of Health and Human Services (HHS). Federal officials have been saying they hope to have the first doses ready to use by mid-October, but some doubt about that date was expressed at today's meeting.

Guidance assumes no adjuvants
The ACIP recommendations assume that the H1N1 vaccines to be used will not contain adjuvants, because using an adjuvant would create regulatory complications that would delay vaccine availability. Adjuvants have not been used with flu vaccines in the United States, but HHS has ordered a supply of adjuvants for possible use in the pandemic.

Early in today's meeting, Dr. Robin Robinson, director of HHS's Biological Advanced Research and Development Authority (BARDA), predicted that about 120 million doses of vaccine could become available in October and another 80 million per month after that. He said the manufacturers so far have made the bulk equivalent of about 20 million doses of injectable vaccine and 12.8 million doses of nasal spray vaccine.

However, he said that one manufacturer, which he didn't name, is having trouble finishing its production of this year's seasonal flu vaccine. "We'll see what impact that has on H1N1. We're working with them," he said.

On the other hand, Robinson said the manufacturers are seeing some improvements in the production yields of the vaccines, which are grown in eggs. Yields have been reported to be only 25% to 50% as high as typical yields for seasonal flu vaccines.

"I'm happy to say that we're starting to see increases in the production yield this week," he said, without offering details.

One or two doses?
A big question mark in the vaccine effort is whether one or two doses will be needed. Federal officials are awaiting early results from clinical trials to find out if one dose will generate a potentially protective immune response, but the general expectation is that two are likely to be necessary, because the virus is new.

In that regard, the ACIP recommended that if supplies are short, providers not turn vaccine seekers away in order to save supplies for second doses.

Even if supplies initially run short, "supply and availability will continue, so the committee stressed that programs and providers continue to vaccinate unimmunized patients and not keep vaccine in reserve for later administration of the second dose," the CDC said in a press release.

Schuchat said the demand for the vaccine is likely to be well below the number of people in the targeted groups.

"We think it's important to differentiate the size of the populations from the number of doses we have and the number we need," she said. Seasonal flu vaccination is recommended for 83% of the population, but actual uptake is less than 40%, she observed, adding, "If we use this as our expectation, we may have plenty of vaccine right away."

Obesity as a potential risk factor
In other comments, Schuchat said obesity by itself may not be a risk factor for serious H1N1 disease, despite some recent evidence to the contrary.

"The information is incomplete," she said. Morbidly obese people seem to have worse complications than normal-weight people, but obese people in general have more health conditions that increase their risk of complications. "When we looked at those who had only obesity or morbid obesity, it's not so clear," she said.

Concerning the vaccination target groups, the new ACIP recommendations call for using the same list of risk factors as are used for seasonal flu, Schuchat said in response to questions. Those include things like chronic respiratory, heart, liver, or kidney disease; diabetes; suppressed immunity, and pregnancy, but not obesity by itself, she said.

Schuchat was asked what she would tell an elderly person about the H1N1 vaccine, given the potential for confusion with different recommendations for seasonal and H1N1 flu vaccination.

"As a provider with the elderly, I'd strongly recommend seasonal flu vaccine, and say that from what we've seen so far with this [H1N1] virus, you're probably going to be spared," she replied.

ACIP recommendations are routinely approved and issued by the CDC. "These recommendations will be reviewed quickly by CDC and we expect them to be rapidly disseminated to state and local health departments," which are actively planning their vaccination programs, Schuchat said.

In response to a question, she said HHS has ordered some thimerosal-free vaccine, both injectable and the nasal spray, but she did not specify quantities. Thimerosal is a mercury-containing compound still used as a preservative in some flu vaccines.

Need for revised guidance
At the meeting, CDC medical epidemiologist Anthony Fiore, MD, MPH, told the committee that though HHS released pandemic vaccine guidance in 2008, new recommendations are needed because the previous ones focused on a more severe scenario. Current evidence suggesting a more moderate pandemic warrants revisions, he said.

Members of the committee struggled over how high to set the age boundary for vaccine prioritization. The initial recommendation presented to the members today from ACIP's Influenza Working Group stipulated that children aged 6 months to 18 years be included among the priority groups. Federal and state officials are eyeing administering the vaccine at schools as an efficient way to reach this group.

One problem that led to the uncertainty over where to place the age cutoff is a lack of clear data on infection rates within the subgroups. During the morning session of the meeting, Fiore said early reporting on confirmed cases revealed an infection rate of 2.56 in 100,000 among 12- to 18-year olds, which decreased to 1.26 per 100,000 among 19- to 24-year-olds.

However, several members spoke in favor of pushing the age cutoff to 24 as a way to include college students. James Turner, MD, a liaison representative from the American College Health Association (ACHA), told the group that college students in dormitory settings have the same risk factors that appear to have played a role in the spread of the virus this summer at camps and military schools. He said flu transmission on college campuses probably would have been higher in the spring, but many students were leaving for the year in May when the virus was gaining a foothold.

Turner said the ACHA's data suggest that the seasonal vaccine immunization rate in college students is about 32%, which he said suggests good uptake in the age-group.

Other members of the group pushed for including the broader age-group as a way to simplify the message about who should be vaccinated. Also, William Schaffner, MD, liaison representative from the National Foundation for Infectious Diseases, warned that vaccine prioritization schemes that are too narrow could result in unused vaccine. Schaffner is chair of the Department of Preventive Medicine at Vanderbilt University School of Medicine in Nashville.

The committee's decision to expand the upper age limit from 18 to 24 adds 24 million people to the priority group, CDC officials said.

See also:

CDC ACIP page

Jul 29 CDC press release

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