Effectiveness of COVID-19 vaccines administered during pregnancy in Spain and Norway

Tuesday, August 27, 2024

8:45 AM – 9:00 AM CEST

Location: Conv Hall I C

Presenting Author(s)

Núria Mercadé-Besora, MS

Rsearch Assistant in Health Data Sciences
University of Oxford, Spain

Slides

Co-Author(s)

NT

Nhung TH Trinh, PharmD, PhD

Postdoctoral Fellow
Pharmacoepidemiology and Drug Safety Research Group, Department of Pharmacy, Faculty of Mathematics and Natural Sciences, University of Oslo, Oslo, Norway, Norway
SH

Saeed Hayati

Pharmacoepidemiology and Drug Safety Research Group, Department of Pharmacy, Faculty of Mathematics and Natural Sciences, University of Oslo, Oslo, Norway, Norway
Berta Raventós, PhD

Postdoctoral researcher
Fundació Institut Universitari per a la recerca a l'Atenció Primària de Salut Jordi Gol i Gurina (IDIAPJGol), Spain
Theresa Burkard, PhD (she/her/hers)

Postdoctoral Data Scientist
University of Oxford
Oxford, United Kingdom
EB

Edward Burn, PhD

Senior Researcher in Epidemiology and Health Economics
University of Oxford, United Kingdom
Martí Català, PhD (he/him/his)

Senior Data Scientist
University of Oxford
Oxford, United Kingdom
AL

Angela Lupattelli, PhD

Professor
Pharmacoepidemiology and Drug Safety Research Group, Department of Pharmacy, Faculty of Mathematics and Natural Sciences, University of Oslo, Oslo, Norway
University of Oslo
Oslo, Norway
LP

Laura Pérez-Crespo, PhD

Fundació Institut Universitari per a la recerca a l'Atenció Primària de Salut Jordi Gol i Gurina (IDIAPJGol)
Barcelona, Spain
Hedvig M.E Nordeng, PhD (she/her/hers)

Professor
Pharmacoepidemiology and Drug Safety Research Group, Department of Pharmacy, University of Oslo (UiO), Oslo, Norway
Oslo, Norway
Talita Duarte-Salles, PhD

Assistant Professor
Erasmus MC and IDIAPJGol
Barcelona, Spain

Background: Pregnant individuals are at risk of severe COVID-19. Vaccination with mRNA-vaccines is recommended and deemed safe for both mother and fetus. However, their effectiveness in this pregnant individuals is still unclear.

Objectives: Evaluate the effectiveness of COVID-19 vaccines administered during pregnancy against SARS-CoV-2 infection.

Methods: We conducted a cohort study with primary care records from Spain and Norway. Enrollment period spanned from December 27, 2020 (start of the vaccination campaign) to 3 months before end of available data (Spain: 03/2022, Norway: 12/2021). The study population included pregnant individuals aged 12 to 55 years with no prior history of COVID-19 vaccination or infection.
The exposure of interest was a first dose of a mRNA-based COVID-19 vaccine during pregnancy. The outcome of interest was maternal SARS-CoV-2 infection (clinical diagnosis or positive PCR/antigen test).
A target trial emulation based on calendar week was conducted to create vaccinated and unvaccinated cohorts. Pregnant individuals vaccinated during the week were matched to an unvaccinated counterpart using exact matching on gestational age (trimesters), maternal age (2-year band), and propensity score (PS) with a 0.2 calliper. The PS included region, previous pregnancies, variables for health care utilization proxy (e.g., time registered in the system, previous COVID-19 tests, Influenza/Tdap vaccination, and healthcare visits), and health conditions prioritizing individuals for vaccination in each country. Both members of the matched pair were censored when the control became vaccinated, and the control could then contribute as vaccinated if a suitable match was found. Index date was vaccination date of the exposed part.
Standardized mean differences (SMD) were estimate for all PS variables, ICD10 sub-chapters, and ATC 3rd level. Covariates with |SMD| > 0.1 were introduced in the outcome model. Negative Control Outcomes (NCO) were used to detect residual bias. Cox regression was adjusted to estimate hazard ratios (HR) with 95% confidence intervals (CI).

Results: We included 13,484 pregnant individuals in Spain, and 7,586 in Norway. In both countries SMD showed covariate balance (|SMD| < 0.1), and NCO results were not associated with vaccination. We found that COVID-19 vaccination reduced risked of maternal SARS-CoV-2 infection in both Spain and Norway. Norwegian results showed a higher risk reduction, HR 0.49 (95% CI 0.39-0.61), compared to Spanish results, HR 0.87 (95% CI 0.80-0.95).

Conclusions: COVID-19 vaccination was associated with a reduced risk of 13% (Spain) and 51% (Norway) against maternal SARS-CoV-2 infection. These findings endorse COVID-19 vaccination during pregnancy.