This year’s flu vaccine was only 36% effective, according to the CDC. Data on nearly 4,600 patients showed that of patients testing positive for influenza, about 43% had received the flu vaccine. The high prevalence of influenza A (H3N2) was the primary culprit, as the vaccine was only 25% effective against this virus. It is notoriously difficult to create a vaccine against H3N2 because of its tendency to mutate during the flu season. Still, the vaccine reduced severe H3N2 illness in children by more than half. The vaccine was more effective against the other circulating viruses this year — H1N1 and influenza B strains (MMWR Morb Mortal Wkly Rep 2018;67:180-185).
The FDA has approved the makeup of the 2018-2019 vaccine. It is very similar to this year’s vaccine. For the trivalent vaccine, the FDA Vaccines and Related Biological Products Advisory Committee has approved H1N1 as well as A/Singapore/INFIMH-16-0019/2016 (H3N2)-like virus, which is a different H3N2 from the 2017-2018 vaccine. One influenza B virus was included in the trivalent vaccine and a second B virus was included in the quadrivalent vaccine. Additionally, the CDC’s Advisory Committee on Immunization Practices gave a lukewarm endorsement to FluMist, the live-attenuated influenza vaccine. The vaccine was not marketed the last two seasons because of poor effectiveness against the H1N1 strain. However, the manufacturer reports it has reformulated the H1N1 component of the vaccine, improving efficacy. FluMist will appear on the recommended vaccine list this fall.