A new comprehensive analysis of flu studies concludes that most flu vaccines provide only moderate protection against influenza, and in some years barely make a difference at all.
The analysis also suggests that the people who most need protection from flu — children and seniors — may be the least likely to derive benefit from vaccines, long considered important to public health.
University of Minnesota infectious disease expert Michael Osterholm and three other national flu researchers led the research effort. Their findings, published Tuesday in the British medical journal, The Lancet, were gleaned from a review of more than two dozen of the most rigorous flu studies done to date.
A PILLAR OF PUBLIC HEALTH
The researchers screened thousands of flu studies published since the 1960s and found only a handful that adequately measured the effectiveness of flu vaccine. They say most of the published studies vastly over-estimated the benefits of receiving the vaccine.
Flu vaccines have long been considered a pillar of public health in the United States. Each fall, government-sponsored awareness campaigns urge Americans to get an influenza vaccination for themselves and their family members. As recently as last year, the Centers for Disease Control and Prevention expanded its flu vaccine recommendations to include everyone six months and older.
Millions of people follow the advice. This flu season, U.S. manufacturers estimate they will distribute as many as 173 million doses of flu vaccine.
The heavy promotion and easy access to the vaccine gives the impression that anyone who is immunized will be protected from flu. But the new analysis of flu studies by researchers in Minnesota, Wisconsin and Maryland suggests that's not the case for many people.
"We found that the vaccine was about 59 percent effective overall in individuals 18 to 65 years of age," said Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota. "Some studies had higher, some had lower."
In other words, on average, more than 40 percent of people who receive a flu vaccine get no protection from it against the flu.
Osterholm said an influenza vaccine ideally should be 85 to 95 percent effective for all age groups to be considered a good vaccine.
"If we had a childhood measles vaccine that only protected on average 59 percent of the time, we'd say that was a failure," he said.
Osterholm's group sifted through 5,707 potential medical articles on the flu that were published from 1967 to 2011. He said fewer than 200 of those articles contained an in-depth analysis on the effectiveness of influenza vaccines. The researchers narrowed that list further by excluding studies that didn't confirm influenza cases with highly sensitive testing or viral cultures.
At the end of the vetting process, Osterholm said, only 31 flu studies met the group's strict criteria. The rest were considered flawed in some way.
"These really are the best studies, the ones that should give us the best information we have," Osterholm said. "And you know we have an old saying in the biostatistics area, 'Garbage in, garbage out.' More data doesn't mean more answers. And we feel very confident that the studies that were included here give us the best chance of really understanding the actual effectiveness or efficacy of influenza vaccine."
Public health officials who have long promoted flu vaccines might be expected to quibble with Osterholm's findings or study design. But Dr. Joseph Bresee, Chief of the Epidemiology and Prevention Branch in the national Centers for Disease Control's Influenza Division, said he has no complaints. Bresee said the 59 percent flu vaccine effectiveness standard is about right.
CDC SLOW TO DOWNGRADE VACCINE EFFICACY, SOME SAY
Bresee said the CDC has been open with the public about the limitations of the flu vaccine and has not oversold it. But several independent researchers contacted by MPR News said the agency has been very slow to acknowledge flu data that shows the vaccine does not work as well as expected.
The researchers declined to speak publicly. But Peter Sandman, a health risk communicator who is familiar with the agency's public communication on flu vaccines, said the CDC only recently downgraded its vaccine effectiveness estimates on its website. Sandman said CDC officials changed the agency's flu vaccine effectiveness standards after they learned that Osterholm's paper would soon be published. He said the CDC did not issue a press release calling attention to the downgrade.
"They were saying 70 to 90 percent effective for a very long time and just a week ago they re-did their flu Q&A — two of them — both for professionals and non-professionals, and switched from 70 to 90 percent to 50 to 70 percent, which is a pretty major change," Sandman said. "They snuck it in."
A spokesman for the CDC confirmed that the agency did recently revise its flu vaccine effectiveness estimate and did not issue a press release. The spokesman added that the CDC's seasonal influenza site is routinely updated each season.
But Sandman said the effectiveness downgrade was significant enough that the CDC should have called more attention to it.
"If people get the impression, I think the accurate impression that public health has been less than candid about the low effectiveness of the flu shot, the scary thing is that people might deduce from that, 'Gee, if you can't trust them on the efficacy of the flu shot, why do we think we can trust them on the safety of vaccines in general?' " he said.
That would be an unfortunate conclusion, Sandman said, and one that he does not think is accurate. But he worries that public health officials may lose credibility with some people based on how they handled the new flu vaccine information.
That could make it tougher for people like Kris Ehresmann to do her job. As director of the Infectious Disease Epidemiology, Prevention and Control Division at the Minnesota Department of Health, Ehresmann spends a lot of time promoting flu vaccines. She wouldn't comment on how the CDC has handled the new flu estimates, but said in the end Osterholm's paper still demonstrated that the vaccines work for many people.
Ehresmann said that's the message she'll continue telling the public.
"If we had an HIV vaccine that became available with limited effectiveness, people would still line up for that vaccine, if it was safe," Ehresmann said. "Clearly, the flu vaccine is very safe."
Osterholm said he has no problem with public health officials promoting the current flu vaccine as long as they admit they're not satisfied with it. He said his findings demonstrate that we need a better vaccine.
STUDY COULD KICK-START VACCINE IMPROVEMENTS
New flu vaccines are in development, but Osterholm believes they won't advance to the market as long as the current vaccine is considered adequate.
"We have to acknowledge the limits of these vaccines because that continues to be the major barrier to investment in new vaccines and companies willing to step up and put a billion dollars on the line, which is the cost it is today to bring a new vaccine forward," he said.
Osterholm's flu review does show the current vaccine can be effective among certain groups of people, depending on their health status and depending on the form of the vaccine.
A subset of the studies showed that the nasal form of the flu vaccine was far more effective than the flu shot in young children. Ten of the randomized trials included in the review showed that the flu vaccine nasal swab was more than 80 percent effective in children age six months to seven years old.
Ehresmann, of the Health Department, said that finding merits a closer look. She sits on the Advisory Committee for Immunization Practices which advises the CDC. The group is meeting in Atlanta this week.
Osterholm's influenza study is not on the committee's agenda for discussion. But Ehresmann said it's likely that at some point her group will discuss the nasal vaccine findings. She said the committee could eventually decide to recommend the nasal form of the vaccine over the flu shot for young children. But she said parents already are free to request whichever form they prefer.