On February 21, CDC’s Advisory Committee on Immunization Practices (ACIP) voted to include the intranasal quadrivalent live attenuated influenza vaccine (LAIV; FluMist—MedImmune/AstraZeneca) in its recommendations for the 2018-19 influenza season. ACIP had recommended against using the vaccine this season and last season, citing concerns about its effectiveness after the vaccine provided poor protection against H1N1 in the 2013-14 and 2014-15 seasons.
Since then, the manufacturer has included a different strain of H1N1 in the vaccine, A/Slovenia. In trials of children between 2 and 4 years old, the manufacturer found that antibody response to the new H1N1 component rose fourfold in 23% of participants after the first dose and in 45% of participants after the second dose, suggesting that the new H1N1 component is more effective than the prior one, A/Bolivia.
Because there has been minimal H1N1 activity over the last two seasons, and because ACIP recommendations against using the vaccine have kept it largely unused in the U.S., the actual effectiveness of the current vaccine in the population is unknown. However, CDC researchers who analyzed prior studies of LAIV found no statistically significant difference between LAIV and inactive influenza vaccine in effectiveness against H3N2 and influenza B viruses.
The committee’s recommendations await approval by CDC acting director Anne Schuchat, MD (RADM, USPHS), and the final recommendations will appear in CDC’s Morbidity and Mortality Weekly Report.