CDC: FDA tweaks flu vaccine after moderate to severe flu season

ATLANTA — The 2014–15 influenza season was moderately severe overall and especially severe in seniors, with the H3N2 virus predominating, the Centers for Disease Control and Prevention reported Friday in the Morbidity and Mortality Weekly Report. 

 

One reason behind last season’s elevated severity was the ineffectiveness of last year's flu vaccine, which was only 19% effective because of a mismatch between the strains included in the vaccine and the predominant circulating strain last season. The majority of circulating influenza A (H3N2) viruses were different from the influenza A (H3N2) component of the 2014–15 Northern Hemisphere seasonal vaccines, and the predominance of these drifted viruses resulted in reduced vaccine effectiveness. 

 

For this coming season, the Food and Drug Administration's Vaccines and Related Biological Products Advisory Committee earlier this year recommended that the 2015–16 influenza trivalent vaccines used in the United States contain an A/California/7/2009 (H1N1)-like virus, an A/Switzerland/9715293/2013 (H3N2)-like virus and a B/Phuket/3073/2013-like (B/Yamagata lineage) virus. Quadrivalent vaccines are also formulated with a B/Brisbane/60/2008-like (B/Victoria lineage) virus. This represents a change in the influenza A (H3) and influenza B (Yamagata lineage) components compared with the composition of the 2014–15 influenza vaccine. 

 

For the 2014-15 season, the cumulative rate of influenza-associated hospitalizations among adults over the age of 65 was 319.2 per 100,000 population, exceeding the cumulative total of 183.2 per 100,000 population for the 2012–13 season, which had previously been the highest recorded rate of laboratory-confirmed, influenza-associated hospitalizations since this type of surveillance began in 2005. Among children younger than 5 years old the cumulative hospitalization rate (57.1 per 100,000 population) was slightly less than that observed during the 2012–13 season (66.2 per 100,000 population). 

 

During the 2014–15 influenza season in the United States, influenza activity increased through late November and December before peaking in late December. Influenza A (H3N2) viruses predominated, and the prevalence of influenza B viruses increased late in the season.