Last season’s flu vaccine provided substantial protection for children
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Data reported during IDWeek showed that the 2019-2020 influenza vaccine was 62% effective among children, including 55% effective against influenza B despite a poor match for circulating B viruses, researchers reported.
For the first time in decades, influenza B viruses — which are more common among children than adults — predominated in the early part of last season, particularly viruses of the B/Victoria lineage.
Angela P. Campbell, MD, MPH, a medical officer in the CDC’s Influenza Division, and colleagues used data from the National Vaccine Surveillance Network on 2,022 inpatients and 2,066 ED patients in seven pediatric hospitals to determine the efficacy of last season’s vaccine among kids.
Of the 2,022 inpatients, 324 (16%) tested positive for influenza — 38% with influenza B/Victoria alone and 44% with influenza A(H1N1) alone. Among the 2,066 ED patients, 653 (32%) tested positive for influenza — 45% with only influenza B/Victoria and 43% with only influenza A(H1N1).
The calculated vaccine effectiveness against any influenza-related hospitalization was 62% (95% CI, 51%-70%), including 55% against influenza B/Victoria (95% CI, 35%-69%) and 68% against influenza A(H1N1) (95% CI, 55%-78%). Vaccine effectiveness against any influenza-related ED visit was 53% (95% CI, 42%–62%).
Adjusted overall influenza vaccine effectiveness for all patients has ranged from a low of 10% to a high of 60% over the past 15 years, according to CDC data. Campbell noted that vaccine effectiveness against influenza B for any age ranged from 34% to 58% between 2011-2012 and 2018-2019, “placing the 55% effectiveness against hospitalizations and ED visits in children from the 2019-2020 season at the high end of the range.”
“This is especially noteworthy given that the circulating B/Victoria viruses differed from the B/Victoria component of the 2019-2020 influenza vaccine,” Campbell told Healio.
“Our results are consistent with other publications that have reported cross-lineage protection for influenza B viruses,” she said. “This further confirms the fact that vaccination can still be protective in children, even when the circulating influenza viruses do not match the vaccine antigens.”
According to the researchers, vaccine effectiveness did not vary significantly by age.
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Campbell AP, et al. Abstract 178. Presented at: IDWeek; Oct. 21-25, 2020 (virtual meeting).
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