How Effective Are Flu Vaccines?
Study Suggests Flu Vaccine Provides Moderate Protection Against Flu
By Salynn Boyles
WebMD Health News
Reviewed By Laura J. Martin, MD
Oct. 25, 2011 -- As flu season approaches, a new analysis finds that the flu vaccine provides only moderate protection against the flu, noting that such protection is greatly reduced or absent during some flu seasons.
The analysis is published in The Lancet.
"While the vaccine does work, and we still recommend that it be used, it does not demonstrate the kind of efficacy that has often been reported," says study researcher Michael T. Osterholm, MD, of the University of Minnesota Center for Infectious Disease Research and Policy.
Information Gap on Vaccine Effectiveness
The researchers also say there is a lack of evidence for the effectiveness of flu vaccines in the most vulnerable groups, such as the elderly.
"For those over age 65 there are real gaps in the information we have about effectiveness compared to young, healthy adults," he says. "It is clear that we need to develop new and better vaccines to fill these gaps."
Osterholm says the analysis represents the most exhaustive review ever conducted of the effectiveness of the flu vaccines used in the U.S.
The researchers screened 5,700 articles and studies, identifying just 31 that used highly specific diagnostic testing to confirm influenza.
Their review of these studies showed that the trivalent inactivated vaccine (TIV) -- which accounts for about 90% of flu vaccines given in the U.S. -- had 59% effectiveness in healthy adults between the ages of 18 and 65.
The vaccine's effectiveness in children, teens, and the elderly could not be determined because no trials involving these groups met the researchers' inclusion standards.
Nasal Spray Vaccine for Children
Ten studies examined the nasal spray flu vaccine in children between the ages of 6 months and 7 years, finding it was effective for of 83% of that group.
The nasal vaccine is approved for use in healthy people ages 2 to 49.
Osterholm tells WebMD that the impressive protection should convince vaccine policy makers to recommend the nasal spray flu vaccine over the injected TIV vaccine in children.
"The [nasal spray flu vaccine] works very well in children, but it has never been preferentially recommended," he says. "We could potentially have a much greater impact in preventing influenza if we were to encourage the use of [the nasal spray flu vaccine] in that group."
Message the Same: 'Get Your Flu Shot'
Andrew Pavia, MD, who chairs the Pandemic Influenza Task Force of the Infectious Diseases Society of America, says the new analysis confirms what has been known about the current flu vaccine.
"Everyone agrees that we need better vaccines and we are making progress in that direction," he tells WebMD. "We have known for years that the vaccine we have does not provide a first-rate level of protection in the elderly and the very young, but it does provide protection. It would be terrible if the message to the public was that getting vaccinated isn't important."
In fact, he says, the less effective a vaccine is, the more important it is that as many eligible people as possible get vaccinated to protect those who are most vulnerable.
"With a vaccine that is less than perfect, which is most of our vaccines, much of the protection comes from having widespread coverage within a community," he says.
Better Vaccines May Be on the Way
Osterholm and colleagues conclude that new vaccines are needed that work in different ways from current ones.
But infectious disease expert William Schaffner, MD, says research focused on making the current vaccines better is already paying off.
"The last five years has seen more research aimed at developing better flu vaccines than the previous 50," he says.
Two new vaccines have been licensed within the last two years: a high-dose vaccine that is expected to provide better protection for people over 65 and an intradermal vaccine delivered with a needle that is much smaller than traditional needles.
Schaffner says there is also optimism that a universal vaccine covering all strains of the influenza virus may be on the horizon. Because it would deliver a much higher level of protection than current vaccines, it could be given every five or 10 years instead of every year, he says.
Pavia agrees that the universal vaccine, which he calls the Holy Grail of flu vaccine research, may soon be a reality thanks to recent scientific breakthroughs.
"We have a clear path forward that could get us there within the decade," he says.
Osterholm, M.T. The Lancet, Oct. 26, 2011.
Michael T. Osterholm, PhD, MPH, Center for Infectious Disease Research and Policy, University of Minnesota.
Andrew T. Pavia, MD, chairman, Pandemic Influenza Task Force, Infectious Diseases Society of America.
William Schaffner, MD, chairman, department of preventive medicine; professor of preventive medicine, Vanderbilt University Medical Center, Nashville.
News release, The Lancet.
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