Flu vaccine most effective against type B

European studies suggest that the seasonal influenza vaccine offers effective protection against influenza B viruses, but only moderate protection against influenza A.

The findings, which were recently reported in the journal Eurosurveillance, are consistent with earlier results reported in the United States. The European study combined data from five countries, according to CIDRAP News.

The vaccine's effectiveness against influenza B was estimated to be approximately 78 percent, but only around 62 percent and 42 percent against the two common strains of influenza. Overall, the vaccines effectiveness is estimated to be approximately 62 percent.

Navarre, Spain, reported an even higher effectiveness rate against influenza B. The vaccine stopped the virus in 86 percent of cases, according to an additional report.

Both studies parallel a January effectiveness report produced by the U.S. Centers for Disease Control and Prevention. The CDC early-season estimate showed the vaccine to be 70 percent effective against type B in the United States and 55 percent against type A. Overall, it was 62 percent effective, CIDRAP News reports.

The Eurosurveillance report is accompanied by an editorial discussing the difficulties in assessing the effectiveness of vaccines made from inactive flu, including recent evidence that having a good match between circulating strains and vaccine does not necessarily lead to increased effectiveness.