Study Finds Nasal Flu Vaccine Less Effective Than the Flu Shot

In a recent meta-analysis of pooled individual patient-level data, researchers found reduced effectiveness of the quadrivalent live-attenuated influenza vaccine (LAIV4) against influenza A/H1N1pdm09 compared with inactivated influenza vaccine (IIV) in children and adolescents.

The meta-analysis looked at data from five U.S. studies from the 2013–2014 flu season through the 2015–2016 flu season to compare the vaccine effectiveness of LAIV4 and IIV against medically attended, laboratory-confirmed influenza among patients ages 2 years to 17 years by influenza season, subtype, age group and prior vaccination status. The vaccine effectiveness of IIV or LAIV4 was calculated as 100%Å~(1−odds ratio), comparing the odds of vaccination among patients who were influenza-positive to patients who were influenza-negative from adjusted logistic regression models. Relative effectiveness was defined as the odds of influenza comparing LAIV4 and IIV recipients.

Of 17, 173 patients ages 2 years to 17 years, 4,579 received IIV, 1,979 received LAIV4 and 10, 615 were unvaccinated. Against influenza A/H1N1pdm09, vaccine effectiveness was 67 percent for IIV and 20 percent for LAIV4. Results were similar when stratified by vaccination in the previous season. LAIV4 recipients had significantly higher odds of influenza A/H1N1pdm09 compared with IIV recipients. LAIV4 and IIV had similar effectiveness against influenza A/H3N2 and B. According to the researchers, overall findings were consistent when stratified by influenza season and age group.

The Advisory Committee on Immunization Practices provided an interim recommendation against LAIV4 use during the 2016-2017 and 2017-2018 seasons. However, AstraZeneca, manufacturer of LAIV4, implemented an improved strain selection process for the vaccine in the 2017-2018 flu season. Data showed improved viral shedding and immunogenicity in young children. And, Public Health England (PHE) published provisional end-of-season adjusted vaccine effectiveness estimates from the 2017-2018 season, which demonstrated LAIV4 provided statistically significant vaccine effectiveness against A/H1N1 strains during the 2017-2018 season in children 2 years to 17 years of age.