Influenza vaccine provided dismal protection against this winter's virus, early data suggest

Canadian influenza researchers reported in the journal Eurosurveillance that the influenza vaccine is not doing a very good job protecting against H3N2 viruses this year in North America. Their midseason estimate, based on data from the four provinces where approximately 80% of Canadians live, suggested that the H3N2 component of the vaccine is 17% effective at preventing infection. Last year it was estimated at 37% in Canada and 34% in the United States. Public health authorities have come to expect protection against H3N2 to be in the low-to-mid 30% range at best. The fact that it was so much lower came as a surprise to CDC's influenza experts. "It was lower than what the Canadians or we experienced last year," says Alicia Fry, head of epidemiology for CDC's influenza division. Given that there haven’t been major changes in the viruses, "it is a surprising result." Fry says the CDC surveillance network will stop collecting data for their interim analysis next week, and the agency will publish their findings mid-month. The new research also indicated that in Canada a new subgroup of the H3N2 clan has become the dominant H3N2 viruses causing illness this season. It may be that the vaccine is not targeting that group of viruses effectively. The United States is seeing a similar pattern, says Jacqueline Katz, deputy director of CDC's influenza division.