Combined results of five studies conducted from 2013 to 2016 show the nasal spray or live attenuated influence vaccine (LAIV4) was less effective against influenza A/H1N1 than the injected, inactivated form of the flu vaccine (IIV) in all pediatric age groups.
The meta-analysis, “Live Attenuated and Inactivated Influenza Vaccine Effectiveness,” will be published in the February 2019 issue of Pediatrics.
The analysis documents some of the data, previously reviewed by the American Academy of Pediatrics (AAP) and the Centers for Disease Control and Prevention (CDC), that led to these groups not recommending the nasal spray vaccine during the 2016-17 and 2017-18 seasons. Individual U.S. studies had suggested LAIV4 offered less protection against H1N1, compared with IIV, since the 2013–14 flu season. However, estimated effectiveness by age and prior season vaccination status had been limited by small sample sizes.
For this pooled, individual patient-level data analysis of vaccine effectiveness, researchers looked at how many children who received either LAIV4 or IIV developed laboratory-confirmed cases of the flu in these five studies. Of 17,173 patients aged 2–17 years, 4,579 received IIV, 1,979 received LAIV4, and 10,615 were unvaccinated. It was found that vaccine effectiveness against influenza A/H1N1 was 67 percent (confidence interval 62 percent to 72 percent) for IIV and 20 percent (confidence interval -6 percent to 39 percent) for LAIV4. LAIV4 recipients had significantly higher odds of influenza A/H1N1 infection compared with IIV recipients (OR=2.66; confidence interval 2.06 to 3.44). Results were similar when separated by prior season vaccination status.
Vaccine effectiveness against influenza A/H3N2 and influenza B were similar for both types of flu vaccine. During the current 2018-19 flu season, the AAP recommends IIV as the primary choice for children because the effectiveness of LAIV4 against H1N1 was inferior during these past influenza seasons and is yet unknown for this season.
Additional Information from HealthyChildren.org: