In children and adolescents aged 2 to 17 years, the quadrivalent live attenuated vaccine was less effective against influenza A/H1N1pdm09 compared with inactivated influenza vaccine (IIV), though both had similar effectiveness against influenza A/H3N2 and influenza B, according to a study published in Pediatrics.

Researchers in this study pooled patient-level data from 5 American influenza vaccine studies from the 2013 to 2014 season through the 2015 to 2016 season to compare the vaccine effectiveness of quadrivalent live attenuated vaccine vs inactivated influenza vaccine for patients aged 2 to 17 years (N=17,173). Vaccine efficacy was calculated from adjusted logistic regression models as 100% × (1 – odds ratio [OR]), comparing the odds of vaccination in patients who were laboratory test-positive for influenza with those who were negative. Relative vaccine effectiveness was defined as the odds of development of influenza in recipients of quadrivalent live attenuated vaccine vs inactivated influenza vaccine.

Of the total 17,173 participants included for analysis, 1979 received quadrivalent live attenuated vaccine, 4579 received inactivated influenza vaccine, and 10,615 were unvaccinated. Vaccine efficacy against influenza A/H1N1pdm09 was 67% for inactivated influenza vaccine (95% CI, 0.62-0.72) and 20% for quadrivalent live attenuated vaccine (95% CI, -0.06 to 0.39). Similar results were seen when data were stratified by previous season vaccination. Significantly higher odds of influenza A/H1N1pdm09 were seen in quadrivalent live attenuated vaccine recipients compared with those who received the inactivated influenza vaccine (OR, 2.66; 95% CI, 2.06-3.44), but similar odds were seen for both vaccines against influenza A/H3N2 and influenza B. Overall results remained consistent after stratification by age group and influenza season.

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Study investigators concluded that their findings were consistent with a recently published meta-analysis, wherein researchers “reported suboptimal effectiveness of [quadrivalent live attenuated vaccine] against influenza A/H1N1pdm09 compared with [inactivated influenza vaccine] and similar effectiveness against influenza A/H3N2 in 2014–2015 and influenza B viruses. Although [quadrivalent live attenuated vaccine] containing the updated vaccine virus A/Slovenia/2309/2015 was used in Europe and Canada in [the 2017 to 2018 season], a limited circulation of influenza A/H1N1pdm09 hinders the ability to obtain precise effectiveness estimates.”

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Chung JR, Flannery B, Ambrose CS, et al. Live attenuated and inactivated influenza vaccine effectiveness [published online January 7, 2019]. Pediatrics. doi: 10.1542/peds.2018-2094