Flu vaccine efficacy: Time to revise public messages?

Nov 4, 2011 (CIDRAP News) – For many years, public health personnel have cited the estimate of 70% to 90% when talking about the level of protection afforded by seasonal influenza vaccines. But last week's meta-analysis of flu vaccine studies in The Lancet Infectious Diseases—along with several other studies in recent years—has raised the question of whether it's time to change the message about flu vaccines.

The meta-analysis produced little or no evidence of 70% to 90% efficacy for most population groups. The investigators used strict criteria to focus on the most reliable studies, selecting only those that used laboratory-confirmed or lab-excluded influenza as outcomes, among other stringent requirements.

The authors found that evidence from high-quality randomized controlled trials (RCTs) indicates that flu vaccines have an efficacy of about 59% in adults younger than 65. They did find good RCT evidence that the nasal-spray vaccine (live attenuated influenza vaccine, or LAIV) works well in children 6 months to 7 years old, but RCT evidence of the vaccine's efficacy in older children and adults was lacking. And the investigators found very limited evidence of the vaccine's effectiveness in older people, for whom, owing to ethical concerns, vaccine efficacy has not been tested in RCTs.

The report stressed that existing vaccines are the best flu prevention weapon available and should continue to be used, but called for increased efforts to develop better vaccines.

Public health and immunization officials interviewed by CIDRAP News offered a range of views on whether public communications about flu vaccination should be revised in light of the Lancet ID report—and on whether vaccine benefits have been overstated up until now. One official who thinks the study signals a need for changes is Kristen Ehresmann, RN, MPH, director of the Infectious Disease Epidemiology, Prevention and Control Division at the Minnesota Department of Health in St. Paul.

"I definitely think the messages need to change to make sure we're being very clear with the public about what the truth is and what we know," she told CIDRAP News. "It certainly won't help public health if we gloss over the new data."

Others, however, suggest that it's not helpful or necessary to focus on the vaccine effectiveness numbers, with all their nuances and qualifiers. Instead, they advocate simply emphasizing that vaccines provide some protection and are the best flu defense available. They don't necessarily buy the notion that the benefits of vaccination have been overstated.

"I think that the message should continue to be to get vaccinated," said Claire Hannan, MPH, executive director of the Association of Immunization Managers, based in Rockville, Md. To talk about efficacy numbers is not helpful, in her view: "I think it just creates confusion."

Changes in CDC information
As it happens, the Centers for Disease Control and Prevention (CDC) actually changed some of its online education materials dealing with flu vaccine effectiveness less than 2 weeks before the Lancet ID report was published on Oct 25. (CDC officials were aware of the Lancet ID report in advance, as they had heard a preview of the research at the National Influenza Vaccine Summit Meeting in May.)

The changes in the online materials were carefully noted by the risk-communication consulting team of Peter Sandman and Jody Lanard. They took the occasion of the Lancet ID report's release to criticize the CDC over how long it took to change the online guidance and for making the changes without any public announcement.

A CDC online Q&A article for health professionals, updated Oct 12, says that RCTs conducted in 2009 and 2010 suggest that inactivated flu vaccines are 50% to 70% efficacious in adults younger than 65 when the influenza A strains in the vaccine and those in circulation are well matched. The statement does not mention the previously cited estimate of 70% to 90%

In an analysis sent to CIDRAP News, Sandman and Lanard said the CDC should have changed the number sooner, because two of the three cited studies were published in 2009 and one in early 2010. They added, "The October 12 update does not mention that the 50%-70% estimate is a departure from what the CDC has been saying for years. No CDC news release accompanied the update and heralded this significant change."

The CDC also has an online Q&A article for the general public on flu vaccine effectiveness, which was updated Oct 13. The 70%-90% estimate was dropped from this document in February and replaced by a statement that the CDC was reviewing the latest studies on vaccine effectiveness, according to Sandman and Lanard.

The latest version does not mention the 50%-70% estimate for efficacy in nonelderly adults. Instead, it says the flu vaccine in the 2010-11 season was estimated to be about 60% effective overall and mentions a pre-licensing trial of LAIV that showed the vaccine worked in up to 9 out of 10 children. It also says that a 2009 study by Arnold Monto and colleagues revealed that trivalent inactivated vaccine (TIV) "protected 7 out of 10 people" from flu. Sandman and Lanard branded this last statement misleading, because the Monto study covered adults 18 to 49, not all ages.

Sandman and Lanard note that the Lancet ID study has raised some concern that the reduced estimates of efficacy may hurt flu vaccine uptake. "But the more frightening issue, it seems to us, is whether people who learn that the flu vaccination establishment has been systematically hyping flu vaccine effectiveness might lose some of their confidence in the flu vaccine, in other vaccines, and in public health more generally," they wrote.

Numbers not emphasized
In responding to the Sandman-Lanard critique, CDC spokesman Glen Nowak said the agency has generally avoided focusing on vaccine effectiveness numbers in its influenza educational materials, because vaccine effectiveness varies so much and is so unpredictable in any given season. He also said the revisions of the Q&A articles were in the works for a long time and acknowledged that an earlier update might have been appropriate.

"I would caution you about using those specific Web pages as indicators of the full scale of our public and provider educational efforts on flu," Nowak said. "When you look at the full breadth, very few of those actually provide any specific information on flu vaccine effectiveness. We haven't done that in many years."

"While those [numbers] certainly have some use, you can't really tell someone in October or November how well the vaccine is going to protect them," he said. He added that vaccine effectiveness varies by age-group and is affected by a host of factors.

In addition, Nowak said the CDC has found that stressing specific numbers is not very helpful in inducing people to get vaccinated, especially given the impossibility of predicting vaccine effectiveness in any flu season. "When doing communication and messaging, you have to consider, 'What is my communication goal?' For people who are skeptical, I'm not sure that giving them information that plays to their skepticism will increase the chance of getting the flu vaccine," he said.

As for the timing of updating the online Q&A materials, Nowak said the process of reviewing relevant Web pages was under way for more than a year, amid "dynamic and changing" data about flu vaccine effectiveness. Referring to Sandman and Lanard's point that the information should have been updated sooner, he commented, "To recognize that there were other results in published studies that should've been factored in, that made sense."

At the same time, he insisted that the previous 70%-90% estimate for vaccine effectiveness was supported by studies and, in the earlier CDC materials, was "adequately caveated." An archived earlier version of the Q&A for the general public, noted by Sandman and Lanard, says vaccination can reduce the risk of flu by 70%-90% for healthy adults when the vaccine matches well with circulating strains but may be less effective in the elderly and young children. Nowak also said the recent changes in the online Q&A materials are "consistent with" the Lancet ID analysis.

Embracing the data
While some assert that talking about flu vaccine effectiveness details just confuses the public, Ehresmann, who is a member of the Advisory Committee on Immunization Practices (ACIP), takes a different view. Her job includes overseeing immunization programs at the Minnesota Department of Health.

"I definitely think we have to embrace the data to maintain our credibility—and this is important not just for flu but for all our messages," she said. "I think we need to say this is new information that we have, and we need to respond to the science and the data. This is what we can say about flu vaccine now. It's not perfect, but it's still an important tool."

Ehresmann said the findings didn't come as a surprise to her because she had been briefed on them previously, and some other experts have said the findings should come as no surprise to those who follow flu vaccine research. But Ehresmann said the report has surprised many in public health: "I think for other folks in public health it was pretty shocking in the sense that it was very much a departure from that 70% to 90% that had been so often quoted that it had taken on a life of its own. So it's taking public health folks a while to get their head around it."

She said she intends to cite the 59% efficacy estimate in public communications and acknowledge that 70%-90% is too high. "By touching on the 59%, you're not overselling it . . . and you're not trying to hide anything. If you just say it's not perfect and it's the best we have, people don't know that you really saw the data and are acknowledging the data."

"In Minnesota we're taking this sort of 'embrace the data' approach—this is the reality," she said, adding that she's unsure what approach other states will take.

Anti-vaccine sentiments are among the factors that counsel frankness as the best approach, she commented. "We're working with folks who are opposed to vaccination. They call you on everything if you're not straight. So it's best to just be straight about it up front."

Ehresmann's views are in harmony with those expressed earlier by Paul Etkind, senior director of infectious diseases at the National Association of County and City Health Officials (NACCHO). As reported previously, he said that if public health officials go into the specifics of flu vaccine efficacy, they should acknowledge that the numbers are lower than those generally cited previously.

Staying on course
In contrast, Hannan, of the Association of Immunization Managers, doesn't see the Lancet ID report as a reason to change the main messages about flu vaccines. She is more in the don't-focus-on-the-numbers camp.

"I don't think the message should change," she said. "We need to support research and push manufacturers to make improvements in the vaccine, but I think the overall message to get vaccinated should continue."

On whether the benefits of flu vaccination have been oversold, Hannan said, "That's a tough question. I don't know. I've looked at the report, and I've heard people a lot smarter than me go back and forth on the topic. It's hard to study influenza vaccines. It's variable; there are a number of different outcomes depending on what you're looking for."

As for citing efficacy or effectiveness percentages, she said, "I think some of that is lost on the public. Seventy to 90 percent—what does that really mean?" To make a point of telling the public that those numbers are too high would just create confusion, in her view.

On the other hand, she agrees with one particular implication of the Lancet ID study: that the intranasal vaccine should be recommended over the TIV for young children, given the higher efficacy shown in a number of RCTs. "I do think that the ACIP should consider that," she said. "It's up to the committee to really look at that. But I think they should."

Hannan said her sense is that the findings didn't come as much of a surprise to members of her organization, who are mainly immunization directors in state health departments. "I don't think people really saw them as something new," she said. "There has always been an understanding that this vaccine is variable and it's not perfect. I don't think it changed anyone's message."

However, she also said it seems the report is motivating immunization officials to work harder to promote vaccination. "I think it put them a little more on the promotional side," she said.

A more complex view
Christopher J. Harrison, MD, chair of the Vaccine Advocacy Committee of the Pediatric Infectious Diseases Society, offers a more complicated view of the Lancet ID report and its implications for what the public should know about flu vaccines. Harrison is director of the Pediatric Vaccine Treatment and Evaluation Unit at Children's Mercy Hospital and Clinics and a professor of pediatrics at the University of Missouri in Kansas City.

"I think what the meta-analysis showed is what we can prove to be true, not necessarily what is true," Harrison said. Vaccination "is still one of the best weapons, and the numbers used by the different public health groups may be looking at the best case, whereas the meta-analysis looks at the worst case," he added. "There are a number of other studies that are notably robust and point to better numbers."

He didn't mention specifically which studies should have been included. The Lancet ID authors excluded studies that relied on serology (antibody levels) as indicators of influenza infection, because of difficulty in interpreting the findings in vaccinated persons. They also used only those RCTs in which the comparison group received a placebo or a non-flu vaccine, and they excluded flu vaccine challenge studies—those involving intentional exposure to flu—because such cases can differ from natural infection. Also excluded were observational studies that relied on nonspecific outcomes such as mortality and flu-like illness.

Harrison welcomed the report's conclusion that the LAIV works well in young children: "Savvy pediatricians have come to grips with that in their own practices. So we're going to favor that in our practices even though it's not recommended [over the TIV] at the CDC level."

For him, the essential message about flu vaccines should be, "If you're eligible as a child to get the vaccine, get the intranasal one. If you're a young, healthy person, you probably have about two thirds protection [with vaccination]. But the best thing of all is to get enough of us immunized so we have a modest level of herd immunity."

He suggested that vaccination of about 80% of the population would be enough to begin to achieve herd immunity, which would have the effect of improving vaccine effectiveness because people would have fewer exposures to flu viruses.

Harrison also commented, "Don't avoid the vaccine because of the new study. It isn't breaking new ground; it's reminding us of stuff we need to do better. We need to work together and get better vaccines."

Inside baseball?
Another official who sees no need for major changes in what the public health community tells the public about flu vaccine benefits is Jeff Levi, PhD, executive director of the Trust for America's Health (TFAH), a nonprofit advocacy group based in Washington, DC.

"I don't get the sense that anyone oversold flu vaccines," said Levi. "There are always concerns about the right match [between the vaccine and circulating strains], but the bottom line is it's [vaccination] still a good thing to do. I don't think the study challenges that in any way."

Levi also defended the CDC's communication approach on flu vaccination. "My sense of the way the CDC has spoken to the public about it is that it's important protection to have and the response will vary depending on the individual and the match. And I think that's the message people have heard."

And as for what numerical estimates of efficacy should be communicated, Levi commented, "This is a very inside-public-health conversation that has no relevance to the larger community. . . . We can get very technical about the numbers we use, or we can say this is protective and it's a lot better than going without it."

See also:

Oct 25 CIDRAP News story "Strict meta-analysis raises questions about flu vaccine efficacy"

Oct 25 CIDRAP News story "Public health groups say flu vaccine is best tool, despite limitations"

CDC Q&A for health professionals on flu vaccine effectiveness

CDC Q&A for the general public on flu vaccine effectiveness

Earlier version of CDC Q&A for the public

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