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Evaluation

Oral Presentation

Session: Assessing COVID-19 Vaccine Effectiveness

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.