By Robert Roos, News Editor
Mar 21, 2011 (CIDRAP News) – Preliminary studies suggest that this year’s trivalent seasonal flu vaccine used in Europe was less effective against the 2009 H1N1 virus than last year’s monovalent H1N1 vaccine was, possibly because of some degree of mutation in the virus, according to recent reports in Eurosurveillance.
The 2009 H1N1 virus has been the dominant flu strain this season in Europe, unlike in North America, where H3N2, H1N1, and B strains have all been common.
A preliminary study based on surveillance in seven European countries estimated vaccine effectiveness (VE) against all strains at only 42.3%. At the same time, a separate preliminary study from Spain estimated VE at 50% for all flu strains and 72% for 2009 H1N1.
The two analyses don’t cover the whole season, and both reports say more precise and reliable estimates should become available after data for the whole season can be studied.
The two reports and an accompanying editorial cite antigenic drift, or evolution of the virus, as one of several factors that may help explain the lower VE compared with last year’s H1N1 vaccine.