Vaccine Effectiveness Against Pediatric Influenza Hospitalizations and Emergency Visits.

01 Nov 2020
Campbell AP, Ogokeh C, Lively JY, Staat MA, Selvarangan R, Halasa NB, Englund JA, Boom JA, Weinberg GA, Williams JV, McNeal M, Harrison CJ, Stewart LS, Klein EJ, Sahni LC, Szilagyi PG, Michaels MG, Hickey RW, Moffat ME, Pahud BA, Schuster JE, Weddle GM, Rha B, Fry AM, Patel M

BACKGROUND

Influenza A(H1N1)pdm09 viruses initially predominated during the US 2018-2019 season, with antigenically drifted influenza A(H3N2) viruses peaking later. We estimated vaccine effectiveness (VE) against laboratory-confirmed influenza-associated hospitalizations and emergency department (ED) visits among children in the New Vaccine Surveillance Network.

METHODS

We tested children 6 months to 17 years with acute respiratory illness for influenza using molecular assays at 7 pediatric hospitals (ED patients <5 years at 3 sites). Vaccination status sources were parental report, state immunization information systems and/or provider records for inpatients, and parental report alone for ED patients. We estimated VE using a test-negative design, comparing odds of vaccination among children testing positive versus negative for influenza using multivariable logistic regression.

RESULTS

Of 1792 inpatients, 226 (13%) were influenza-positive: 47% for influenza A(H3N2), 36% for A(H1N1)pdm09, 9% for A (not subtyped), and 7% for B viruses. Among 1944 ED children, 420 (22%) were influenza-positive: 48% for A(H3N2), 35% for A(H1N1)pdm09, 11% for A (not subtyped), and 5% for B viruses. VE was 41% (95% confidence interval [CI], 20% to 56%) against any influenza-related hospitalizations, 41% (95% CI, 11% to 61%) for A(H3N2), and 47% (95% CI, 16% to 67%) for A(H1N1)pdm09. VE was 51% (95% CI, 38% to 62%) against any influenza-related ED visits, 39% (95% CI, 15% to 56%) against A(H3N2), and 61% (95% CI, 44% to 73%) against A(H1N1)pdm09.

CONCLUSIONS

The 2018-2019 influenza vaccine reduced pediatric influenza A-associated hospitalizations and ED visits by 40% to 60%, despite circulation of a drifted A(H3N2) clade.