LAIV vs IIV: Which Was Most Effective During the 2015-2016 Flu Season?

The live attenuated influenza vaccine (LAIV) and the inactivated influenza vaccine (IIV) were both effective against influenza in children age 2 to 17 years during the 2015-2016 influenza season, according to a recent study. However, only IIV was significantly effective against influenza A(H1N1)pdm09 in these patients.

LAIV and both trivalent and quadrivalent IIV were available in the United States during the 2015-2016 influenza season.

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For their study, the researchers evaluated 1012 children age 2 to 17 years at 8 different sites from November 30, 2015, to April 15, 2016. All children included in the study had presented to outpatient settings with a less than 5-day history of fever and respiratory symptoms.

Reverse transcriptase-polymerase chain reaction (RT-PCR) testing for influenza was conducted via nasal swabs. Medical record and vaccine registries were used to confirm influenza vaccination. A logistic regression model was implemented to estimate the effectiveness of the influenza vaccines.

Results indicated that 59% of children were unvaccinated, while 31% had received IIV and 10% had received LAIV. The researchers found that 14% of children had influenza A, which was predominantly antigenically similar to the A/California/7/2009 strain, and 10% had influenza B, which was predominantly a B/Victoria lineage.

Ultimately, vaccine effectiveness for all influenza was 46% with LAIV and 65% with IIV. For influenza A(H1N1)pdm09, vaccine effectiveness was 50% with LAIV and 71% with IIV. The odds ratio for vaccine failure with A(H1N1)pdm09 confirmed with RT-PCR was 1.71 in LAIV recipients vs IIV recipients.

“LAIV and IIV demonstrated effectiveness against any influenza among children aged 2-17 years in 2015-2016,” the researchers concluded. “When compared to all unvaccinated children, VE against influenza A(H1N1)pdm09 was significant for IIV but not LAIV.”

—Christina Vogt

Reference:

Poehling KA, Caspard H, Peters TR, et al. 2015-2016 vaccine effectiveness of live attenuated and inactivated influenza vaccines in children in the United States [Published online October 4, 2017]. Clin Infect Dis. https://doi.org/10.1093/cid/cix869.