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.
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."