Vaccine Effectiveness Against Life-Threatening Influenza Illness in US Children

Clin Infect Dis. 2022 Aug 25;75(2):230-238. doi: 10.1093/cid/ciab931.

Abstract

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 aged <18 years admitted to the intensive care unit with acute respiratory infection across 17 hospitals. Respiratory specimens were tested using reverse-transcription polymerase chain reaction for influenza viruses and sequenced. Using a test-negative design, 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.

Keywords: case control; influenza; pediatrics; severity; vaccination.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Case-Control Studies
  • Child
  • Humans
  • Influenza A Virus, H1N1 Subtype*
  • Influenza A Virus, H3N2 Subtype
  • Influenza B virus
  • Influenza Vaccines*
  • Influenza, Human* / epidemiology
  • Influenza, Human* / prevention & control
  • Seasons
  • United States / epidemiology
  • Vaccination
  • Vaccine Efficacy

Substances

  • Influenza Vaccines