This study focuses on two main aspects related to the COVID-19 vaccine. Firstly, we want to understand among pregnant women how many people are getting vaccinated and when they're getting vaccinated (before or during pregnancy). Secondly, we're assessing how well the vaccine works, which means whether it can reduce COVID-19 among vaccinated pregnant women. We're specifically looking at vaccines that have been commonly recommended for pregnant women.
The results of this research will be important for pregnant women who are a particularly vulnerable population. It will help them to know whether vaccination against COVID-19 helps to reduce COVID-19. Furthermore, this research sheds light on the use of the COVID-19 vaccine within pregnant women and those who want to become pregnant. This will be important information for people in charge of decision making on promoting COVID-19 vaccination amongst pregnant women for example, in case the use is low and the vaccine is working well.
Two objectives concerning the SARS-Cov-2 vaccine among pregnant women are pursued. First, to estimate vaccine uptake among pregnant women, and second, to assess vaccine effectiveness as to how well the vaccine reduces infection. All studies will be conducted in pregnant women who are identified using the Matcho. et al. pregnancy algorithm validated in CPRD data mapped to OMOP. The study period will last from the start of the UK SARS-Cov-2 vaccination period on December 8 2020 until January 2023. The study assesses only vaccines recommended during pregnancy (m-RNA based vaccines) as exposure. For the first objective, there will be two studies. First, we will estimate proportions of vaccination use that has happened before pregnancy and, second, that that has happened during pregnancy. For the second objective, there will be two studies as well, one study comparing vaccination to vaccine-naive pregnant women and a second study comparing the booster vaccine compared to the primary vaccination scheme. For both studies, we will perform 1:1 propensity score matching of pregnant women for every week of the study period. Every woman contribute a maximum of one episode each as an exposed and an unexposed pregnant woman. We will follow all women from the vaccination date (first study) and the booster date (second study) - and the same date in the matched control - until the earliest of the outcome, end of pregnancy, end of records or end of study period. We will estimate hazard ration of COVID-19 in exposed compared to unexposed using Cox proportional hazard regression analyses. Vaccine effectiveness / booster effectiveness estimates will be empirically calibrated based on negative control outcome results. When feasible, results will be stratified by trimester of pregnancy and vaccine brand.
In the first study, the measured outcome is SARS-Cov-2 vaccination.
In the second study, the measured outcomes are a diagnosis of COVID-19 or a SARS-Cov-2 positive test result.
Theresa Burkard - Chief Investigator - University of Oxford
Theresa Burkard - Corresponding Applicant - University of Oxford
Antonella Delmestri - Collaborator - University of Oxford
Daniel Prieto-Alhambra - Collaborator - University of Oxford
Edward Burn - Collaborator - University of Oxford
Martí Català Sabaté - Collaborator - University of Oxford
Nuria Mercade Besora - Collaborator - University of Oxford
Wai Yi Man - Collaborator - University of Oxford