Flu vaccines seem to give "moderate protection" that is less effective than thought, according to a new review of research.

In an analysis of 31 studies published in Thursday's issue of the Lancet Infectious Diseases journal, U.S. researchers concluded that since the vaccine often differs from the virus circulating each flu season, the effectiveness averages only 59 per cent in healthy young adults.

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The effectiveness of the flu vaccine averages 59 per cent in healthy young adults, a new review suggests. ((Al Grillo/Associated Press))

That estimate was for the trivalent inactivated vaccine or TIV,  the type of vaccine commonly used in Canada.

The effectiveness of flu vaccines varied from 16 per cent to 76 per cent, estimated Michael Osterholm, an infectious disease specialist at the University of Minnesota, and his colleagues.

There was too little high-quality information about how well the vaccine works in children and the elderly — two groups that are most at risk from flu-related illness or death.

"We need new and better vaccines," Osterholm said. "We liken the current vaccines to kind of a 1.0 iPhone level and what we need is a 10.0."

In particular, the study's authors said, the amount of protection isn't enough during a pandemic.

"Influenza vaccines can provide moderate protection against virologically confirmed influenza, but such protection is greatly reduced or absent in some seasons," the study's authors concluded.

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The researchers reviewed studies that tested for flu virus in lab tests instead of a faster method that looks for an increase in flu antibodies, which the researchers said tends to overestimate vaccine effectiveness.

The American analysis could help public health planners figure out how to get the biggest bang for the vaccine buck while better vaccines are developed, said Dr. Scott Halperin, director of the  Canadian Centre for Vaccinology in Halifax.

"A lot of research is going on in the flu vaccine field to get a better vaccine," said Halperin. "But having said that, you know 59 or 60 per cent is still far better than zero per cent."

Vaccine technology is improving and more effective vaccines may already be in the works, Halperin said.

The study was funded by the Alfred P. Sloan Foundation.

With files from CBC's Pauline Dakin