Effect of Vaccination on Preventing Influenza-Associated Hospitalizations Among Children During a Severe Season Associated with B/Victoria Viruses, 2019-2020.
BACKGROUND: The 2019-2020 influenza season was characterized by early onset with B/Victoria followed by A(H1N1)pdm09 viruses. Emergence of new B/Victoria viruses raised concerns about possible vaccine mismatch. We estimated vaccine effectiveness (VE) against influenza-associated hospitalizations and emergency department (ED) visits among U.S. children.
METHODS: We assessed VE among children 6 months-17 years with acute respiratory illness and ≥10 days of symptoms enrolled at 7 pediatric medical centers in the New Vaccine Surveillance Network. Combined mid-turbinate/throat swabs were tested for influenza virus using molecular assays. Vaccination history was collected from parental report, state immunization information systems, and/or provider records. We estimated VE from a test-negative design using logistic regression to compare odds of vaccination among children testing positive versus negative for influenza.
RESULTS: Among 2029 inpatients, 335 (17%) were influenza positive: 37% with influenza B/Victoria alone and 44% with influenza A(H1N1)pdm09 alone.VE was 62% (95% confidence interval [CI], 52%-71%) for influenza-related hospitalization, 54% (95% CI, 33%-69%) for B/Victoria viruses and 64% (95% CI, 49%-75%) for A(H1N1)pdm09. Among 2102 ED patients, 671 (32%) were influenza positive: 47% with influenza B/Victoria alone and 42% with influenza A(H1N1)pdm09 alone. VE was 56% (95% CI, 46%-65%) for an influenza-related ED visit, 55% (95% CI, 40%-66%) for B/Victoria viruses and 53% (95% CI, 37%-65%) for A(H1N1)pdm09.
CONCLUSIONS: Influenza vaccination provided significant protection against laboratory-confirmed influenza-associated hospitalizations and ED visits associated with the two predominantly circulating influenza viruses among children, including against the emerging B/Victoria virus subclade.
Clinical infectious diseases : an official publication of the Infectious Diseases Society of America
Influenza; children; test negative design; vaccination
Campbell AP, Ogokeh C, Weinberg GA, et al. Effect of Vaccination on Preventing Influenza-Associated Hospitalizations Among Children During a Severe Season Associated with B/Victoria Viruses, 2019-2020 [published online ahead of print, 2021 Jan 27]. Clin Infect Dis. 2021;ciab060. doi:10.1093/cid/ciab060