As Americans line up for flu shots, they should consider that the vaccines may be far less effective than thought, according to a new study.
Michael Osterholm, an infectious disease specialist at the University of Minnesota, and his colleagues found that the most common flu vaccine in the United States is effective for 59 per cent of healthy adults, well below the 70 per cent to 90 per cent level previously reported.
"We're stuck with a vaccine that has been around for 60 years and not changed much," Osterholm said in recorded remarks. He stressed the need for a new generation of flu shots, particularly in the face of a future pandemic.
There is also a lack of information about how well the vaccine works in children and in adults over the age of 65, he said. These two groups are most at risk from flu-related illness or death.
US health officials recommend that all Americans over six months of age get a flu shot. Nearly 131 million people, or 43 per cent of the US population, received the influenza vaccine last season, according to the Centers for Disease Control and Prevention (CDC).
Sanofi, GlaxoSmithKline, Novartis, the AstraZeneca unit MedImmune, and CSL make vaccines for the US market.
While Osterholm does not dispute the need for the current vaccines, he said the common perception that they are "good enough" hinders the development of novel therapies.
In a study published in The Lancet Infectious Diseases journal, Osterholm and colleagues screened 5,707 vaccine studies published in the last 40 years.
They narrowed their analysis to 31 studies that tested for the presence of flu in laboratory tests rather than counting an increase in flu antibodies -- a faster method but one that researchers say tends to overestimate the vaccine's efficacy.
They also limited results to those that used randomized controlled trials or other observational methods that did not have "selection bias," which could lead to sicker people getting excluded from the study.
A meta-analysis of the 31 studies also showed that a newer type of vaccine that uses a live virus was 83 per cent effective in protecting children between six months and seven years old.
However, this type of vaccine, which is made by MedImmune, is not currently recommended as the best treatment for children by the CDC group that decides immunization practices in the United States, the study's authors said.
The Lancet study was published ahead of a meeting of this group on Wednesday.