Vaccine effectiveness for prevention of covid-19 related hospital admission during pregnancy in England during the alpha and delta variant dominant periods of the SARS-CoV-2 pandemic: population based cohort study

Matthew L Bosworth; Ryan Schofield; Daniel Ayoubkhani; Loes Charlton; Vahé Nafilyan; Kamlesh Khunti; Francesco Zaccardi; Clare Gillies; Ashley Akbari; Marian Knight; Rachael Wood; Pia Hardelid; Luisa Zuccolo; Camille Harrison

doi:10.1136/bmjmed-2022-000403

Vaccine effectiveness for prevention of covid-19 related hospital admission during pregnancy in England during the alpha and delta variant dominant periods of the SARS-CoV-2 pandemic: population based cohort study

BMJ Med. 2023 Jul 10;2(1):e000403. doi: 10.1136/bmjmed-2022-000403. eCollection 2023.

Authors

Matthew L Bosworth¹, Ryan Schofield¹, Daniel Ayoubkhani^{1

2}, Loes Charlton¹, Vahé Nafilyan^{1

3}, Kamlesh Khunti², Francesco Zaccardi², Clare Gillies², Ashley Akbari⁴, Marian Knight⁵, Rachael Wood^{6

7}, Pia Hardelid⁸, Luisa Zuccolo^{9

10}, Camille Harrison¹

Affiliations

¹ Office for National Statistics, Newport, UK.
² Real World Evidence Unit, Diabetes Research Centre, University of Leicester, Leicester, UK.
³ London School of Hygiene and Tropical Medicine, London, UK.
⁴ Population Data Science, Swansea University Medical School, Swansea University, Swansea, UK.
⁵ National Perinatal Epidemiology Unit, Nuffield Department of Population Health, University of Oxford, Oxford, UK.
⁶ Public Health Scotland, Edinburgh, UK.
⁷ The University of Edinburgh Usher Institute of Population Health Sciences and Informatics, Edinburgh, UK.
⁸ NIHR Great Ormond Street Hospital Biomedical Research Centre, UCL Great Ormond Street Institute of Child Health, London, UK.
⁹ Health Data Science Centre, Fondazione Human Technopole, Milan, Italy.
¹⁰ MRC Integrative Epidemiology Unit, University of Bristol, Bristol, UK.

Abstract

Objective: To estimate vaccine effectiveness for preventing covid-19 related hospital admission in individuals first infected with the SARS-CoV-2 virus during pregnancy compared with those of reproductive age who were not pregnant when first infected with the virus.

Design: Population based cohort study.

Setting: Office for National Statistics Public Health Data Asset linked dataset, providing national linked census and administrative data in England, 8 December 2020 to 31 August 2021.

Participants: 815 477 females aged 18-45 years (mean age 30.4 years) who had documented evidence of a first SARS-CoV-2 infection in the NHS Test and Trace or Hospital Episode Statistics data.

Main outcome measures: Hospital admission where covid-19 was recorded as the primary diagnosis. Cox proportional hazards models, adjusted for calendar time of infection, sociodemographic factors, and pre-existing health conditions related to uptake of the covid-19 vaccine and risk of severe covid-19 outcomes, were used to estimate vaccine effectiveness as the complement of the hazard ratio for hospital admission for covid-19.

Results: Compared with pregnant individuals who were not vaccinated, the adjusted rate of hospital admission for covid-19 was 77% (95% confidence interval 70% to 82%) lower for pregnant individuals who had received one dose and 83% (76% to 89%) lower for those who had received two doses of vaccine. These estimates were similar to those found in the non-pregnant group: 79% (77% to 81%) for one dose and 83% (82% to 85%) for two doses of vaccine. Among those who were vaccinated >90 days before infection, having two doses of vaccine was associated with a greater reduction in risk than one dose.

Conclusions: Covid-19 vaccination was associated with reduced rates of hospital admission in pregnant individuals infected with the SARS-CoV-2 virus, and the reduction in risk was similar to that in non-pregnant individuals. Waning of vaccine effectiveness occurred more quickly after one than after two doses of vaccine.

Keywords: COVID-19; Epidemiology; Public health.

Grants and funding

MC_PC_20058/MRC_/Medical Research Council/United Kingdom