Hood et al’s (2023) objective was to examine the effectiveness of inactivated influenza vaccine against outpatient influenza illness in the paediatric population over nine influenza seasons after the 2009 A(H1N1) pandemic.
During the 2011-2012 to the 2019-2020 influenza seasons at outpatient clinics at five sites of the US Influenza Vaccine Effectiveness Network, children aged six months to 17 years with an acute respiratory illness were tested for influenza using real-time, reverse-transcriptase polymerase chain reaction. Vaccine effectiveness was estimated using a test-negative design.
Among 24 148 enrolled children, 28% overall tested positive for influenza, 3 017 tested positive for influenza A(H3N2),
1 459 for influenza A(H1N1)pdm09, and 2 178 for influenza B. Among all enrollees, 39% overall were vaccinated, with 29% of influenza cases and 43% of influenza-negative controls vaccinated. Across all influenza seasons, the pooled VE for any influenza was 46% (95% confidence interval, 43-50). Overall and by type/subtype, VE against influenza illness was highest among children in the six to 59-month age group compared with older paediatric age groups. VE was lowest for influenza A(H3N2) virus infection.
Analysis of many seasons suggested substantial benefit against outpatient illness. Investigation of host-specific or virus-related mechanisms that may result in differences by age and virus type/subtype may help further efforts to promote increased vaccination coverage and other influenza-related preventative measures.
Source: Centers for Disease Control and Prevention