Effectiveness of Influenza Vaccination of Pregnant Women for Prevention of Maternal and Early Infant Influenza-Associated Hospitalizations in South Africa: A Prospective Test-Negative Study

Marta C Nunes; Sibongile Walaza; Susan Meiring; Heather J Zar; Gary Reubenson; Meredith McMorrow; Stefano Tempia; Liza Rossi; Raphaela Itzikowitz; Kate Bishop; Azwifarwi Mathunjwa; Amy Wise; Florette K Treurnicht; Orienka Hellferscee; Matt Laubscher; Natali Serafin; Clare L Cutland; Shabir A Madhi; Cheryl Cohen

doi:10.1093/ofid/ofac552

Effectiveness of Influenza Vaccination of Pregnant Women for Prevention of Maternal and Early Infant Influenza-Associated Hospitalizations in South Africa: A Prospective Test-Negative Study

Open Forum Infect Dis. 2022 Oct 19;9(11):ofac552. doi: 10.1093/ofid/ofac552. eCollection 2022 Nov.

Authors

Marta C Nunes^{1

2}, Sibongile Walaza^{3

4}, Susan Meiring^{3

4

5}, Heather J Zar⁶, Gary Reubenson⁷, Meredith McMorrow⁸, Stefano Tempia^{4

8}, Liza Rossi³, Raphaela Itzikowitz³, Kate Bishop³, Azwifarwi Mathunjwa³, Amy Wise⁹, Florette K Treurnicht³, Orienka Hellferscee^{3

4}, Matt Laubscher^{1

2}, Natali Serafin^{1

2}, Clare L Cutland^{1

2

10}, Shabir A Madhi^{1

2

10}, Cheryl Cohen^{3

4}

Affiliations

¹ South African Medical Research Council, Faculty of Health Sciences, Vaccines and Infectious Diseases Analytics Research Unit, University of the Witwatersrand, Johannesburg, South Africa.
² Department of Science and Technology/National Research Foundation, Faculty of Health Sciences, South African Research Chair Initiative in Vaccine Preventable Diseases, University of the Witwatersrand, Johannesburg, South Africa.
³ Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases, Johannesburg, South Africa.
⁴ School of Public Health, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa.
⁵ Division of Public Health Surveillance and Response, National Institute for Communicable Diseases, Johannesburg, South Africa.
⁶ Department of Paediatrics and Child Health, and South African Medical Research Council Unit on Child and Adolescent Health, University of Cape Town, Cape Town, South Africa.
⁷ Department of Paediatrics and Child Health, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa.
⁸ Influenza Division, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.
⁹ Department of Obstetrics and Gynaecology, Rahima Moosa Mother and Child Hospital, University of the Witwatersrand, Johannesburg, South Africa.
¹⁰ African Leadership in Vaccinology Expertise, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa.

Abstract

Background: Influenza vaccination during pregnancy reduces influenza-associated illness in the women and their infants, but effectiveness estimates against influenza-associated hospitalization are limited and lacking from settings with high human immunodeficiency virus (HIV) infection prevalence. We assessed the effect of maternal vaccination in HIV-uninfected women and women with HIV in preventing influenza-associated hospitalizations in infants and the women.

Methods: During 2015-2018, influenza vaccination campaigns targeting pregnant women were augmented at selected antenatal clinics; these were coupled with prospective hospital-based surveillance for acute respiratory or febrile illness in infants aged <6 months and cardiorespiratory illness among pregnant or postpartum women. Vaccine effectiveness (VE) was assessed using a test-negative case-control study.

Results: Overall, 71 influenza-positive and 371 influenza-negative infants were included in the analysis; mothers of 26.8% of influenza-positive infants were vaccinated during pregnancy compared with 35.6% of influenza-negative infants, corresponding to an adjusted VE (aVE) of 29.0% (95% confidence interval [CI], -33.6% to 62.3%). When limited to vaccine-matched strains, aVE was 65.2% (95% CI, 11.7%-86.3%). For maternal hospitalizations, 56 influenza-positive and 345 influenza-negative women were included in the analysis, with 28.6% of influenza-positive women being vaccinated compared with 38.3% of influenza-negatives, for an aVE of 46.9% (95% CI, -2.8% to 72.5%). Analysis restricted to HIV-uninfected women resulted in 82.8% (95% CI, 40.7%-95.0%) aVE. No significant aVE (-32.5% [95% CI, -208.7% to 43.1%]) was detected among women with HIV.

Conclusions: Influenza vaccination during pregnancy prevented influenza-associated hospitalizations among young infants when infected with vaccine strains and among HIV-uninfected women.

Keywords: influenza; pregnancy; vaccine.