Vaccine: X (Dec 2019)

Influenza vaccine effectiveness against hospitalizations in children and older adults—Data from South America, 2013–2017. A test negative design

  • Carmen Sofia Arriola,
  • Nathalie El Omeiri,
  • Eduardo Azziz-Baumgartner,
  • Mark G. Thompson,
  • Viviana Sotomayor-Proschle,
  • Rodrigo A. Fasce,
  • Martha Von Horoch,
  • José Enrique Carrizo Olalla,
  • Walquíria Aparecida Ferreira de Almeida,
  • Jacqueline Palacios,
  • Rakhee Palekar,
  • Paula Couto,
  • Miguel Descalzo,
  • Alba María Ropero-Álvarez,
  • Cecilia Gonzalez,
  • Sergio Loayza,
  • Natalia Vergara,
  • Patricia Bustos,
  • Winston Andrade,
  • Carla Magda S. Domingues,
  • Ernesto Issac Montenegro Renoiner,
  • Érica Tatiane da Silva,
  • Swamy Lima Palmeira,
  • Daiana Araujo da Silva,
  • Ana Carolina de Lacerda Sousa,
  • Marilda Mendonça Siqueira,
  • Cynthia Vazquez,
  • Silvia Battaglia,
  • Carla Vizzotti,
  • Elsa Baumeister,
  • Carlos Giovacchini,
  • Nathalia Katz,
  • Oscar Pacheco,
  • Juliana Barbosa,
  • Diana Malo,
  • Paola Pulido,
  • Diego Garcia,
  • Consuelo Pinzón

Journal volume & issue
Vol. 3

Abstract

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Background: In 2013, the Pan American Health Organization established a multi-site, multi-country network to evaluate influenza vaccine effectiveness (VE). We pooled data from five consecutive seasons in five countries to conduct an analysis of southern hemisphere VE against laboratory-confirmed influenza hospitalizations in young children and older adults. Methods: We used a test-negative design to estimate VE against laboratory-confirmed influenza in hospitalized young children (aged 6─24 months) and older adults (aged ≥60 years) in Argentina, Brazil, Chile, Colombia, and Paraguay. Following country-specific influenza surveillance protocol, hospitalized persons with severe acute respiratory infections (SARI) at 48 sentinel hospitals (March 2013–December 2017) were tested for influenza virus infection by rRT-PCR. VE was estimated for young children and older adults using logistic random effects models accounting for cluster (country), adjusting for sex, age (months for children, and age-in-year categories for adults), calendar year, country, preexisting conditions, month of illness onset and prior vaccination as an effect modifier for the analysis in adults. Results: We included 8426 SARI cases (2389 children and 6037 adults) in the VE analyses. Among young children, VE against SARI hospitalization associated with any influenza virus was 43% (95%CI: 33%, 51%) for children who received two doses, but was 20% (95%CI: −16%, 45%) and not statistically significant for those who received one dose in a given season. Among older adults, overall VE against SARI hospitalization associated with any influenza virus was 41% (95%CI: 28%, 52%), 45% (95%CI: 34%, 53%) against A(H3N2), 40% (95%CI: 18%, 56%) against A(H1N1)pdm09, and 20% (95%CI: −40%, 54%) against influenza B viruses. Conclusions: Our results suggest that over the five-year study period, influenza vaccination programs in five South American countries prevented more than one-third of laboratory confirmed influenza-associated hospitalizations in young children receiving the recommended two doses and vaccinated older adults. Keywords: Influenza vaccine effectiveness, Children, Adults, Southern hemisphere, Latin America, Severe acute respiratory infections, Test-negative case-control design, Hospitalizations