To keep up with the latest influenza outbreaks caused by strains that are not included in the current vaccine, the U.S. Food and Drug Administration (FDA) advisory committee recommended that producers use three new flu strains in next season’s vaccine, replacing all three components of this year’s version.
Of the flu viruses analyzed by the Centers for Disease Control so far this season, 83% have been type A and 16% type B. Type B viruses tend to cause milder illness than type A viruses. Of the type A viruses, 63% have been H3N2 and 37% have been H1N1. H1N1 virus, which in the United States has been well matched by the vaccine was common until early January, but since then the situation has reversed. Seasons in which H3N2 viruses are predominant tend to be more severe than those in which H1N1 strains predominate, experts say.
The three flu virus varieties in the next season’s vaccine include a type A/H1N1, type A/H3N2, and a type B. The World Health Organization (WHO) recommended replacing all three strains for next year’s vaccine because the majority of recent H1N1 isolates differ from the H1N1 strain in the vaccine.
The flu vaccine is reformulated each year to try to keep pace with the fast-evolving viruses. The WHO and FDA recommend the strains for the vaccine in February to give manufacturers time to grow the viruses in chicken eggs and process them into vaccine doses. The choice of strains can be tricky since the predominant viruses may differ from those in the vaccine, but most years the vaccine is reasonably on target.
Source: CDC
- Have you received a flu shot this season? If no, why not?
- Although flu shots are recommended by various health organizations, do you think it is necessary to get it?
