Vaccine Effectiveness Against Life-Threatening Influenza Illness in US Children.
BACKGROUND: Predominance of 2 antigenically drifted influenza viruses during the 2019-2020 season offered an opportunity to assess vaccine effectiveness against life-threatening pediatric influenza disease from vaccine-mismatched viruses in the United States.
METHODS: We enrolled children ageddesign, we estimated vaccine effectiveness comparing odds of vaccination in test-positive case patients vs test-negative controls, stratifying by age, virus type, and severity. Life-threating influenza included death or invasive mechanical ventilation, vasopressors, cardiopulmonary resuscitation, dialysis, or extracorporeal membrane oxygenation.
RESULTS: We enrolled 159 critically ill influenza case-patients (70% ≤8 years; 51% A/H1N1pdm09 and 25% B-Victoria viruses) and 132 controls (69% were aged ≤8 years). Among 56 sequenced A/H1N1pdm09 viruses, 29 (52%) were vaccine-mismatched (A/H1N1pdm09/5A+156K) and 23 (41%) were vaccine-matched (A/H1N1pdm09/5A+187A,189E). Among sequenced B-lineage viruses, majority (30 of 31) were vaccine-mismatched. Effectiveness against critical influenza was 63% (95% confidence interval [CI], 38% to 78%) and similar by age. Effectiveness was 75% (95% CI, 49% to 88%) against life-threatening influenza vs 57% (95% CI, 24% to 76%) against non-life-threating influenza. Effectiveness was 78% (95% CI, 41% to 92%) against matched A(H1N1)pdm09 viruses, 47% (95% CI, -21% to 77%) against mismatched A(H1N1)pdm09 viruses, and 75% (95% CI, 37% to 90%) against mismatched B-Victoria viruses.
CONCLUSIONS: During a season when vaccine-mismatched influenza viruses predominated, vaccination was associated with a reduced risk of critical and life-threatening influenza illness in children.
Clinical infectious diseases : an official publication of the Infectious Diseases Society of America
Case-Control Studies; Child; Humans; Influenza A Virus, H1N1 Subtype; Influenza A Virus, H3N2 Subtype; Influenza B virus; Influenza Vaccines; Influenza, Human; Seasons; United States; Vaccination; Vaccine Efficacy
case control; influenza; pediatrics; severity; vaccination
Olson SM, Newhams MM, Halasa NB, et al. Vaccine Effectiveness Against Life-Threatening Influenza Illness in US Children. Clin Infect Dis. 2022;75(2):230-238. doi:10.1093/cid/ciab931