Miscarrage after mRNA vaccine

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Observed-to-Expected Fetal Losses Following mRNA COVID-19 Vaccination in Early Pregnancy

The clinical trials used to approve COVID-19 vaccines excluded pregnant women,

and existing safety assessments of COVID-19 vaccination,

particularly during early stages of pregnancy,

are limited to observational studies prone to various types of potential bias, including healthy vaccinee bias.

Methods

March 1, 2016 and February 28, 2022

N = 226,395 pregnancies

Observed-to-expected comparisons

mRNA COVID-19 vaccination, weeks 8-13 and 14-27

Influenza during gestational weeks 8-27 and women vaccinated prior to pregnancy for COVID-19 or influenza, used as controls.

Expected number of fetal losses, historical data from 2016-2018

(that incorporates individual-level risk factors)

A simulated trial, where each vaccinated pregnant woman included in the cohort was ‘matched’ with a ‘synthetic unvaccinated control’ with similar individual and pregnancy characteristics.

Results

COVID-19 vaccination with dose 1 during weeks 8-13

Associated with higher-than-expected fetal losses

13 versus 9 expected for every 100 exposed pregnancies

3.85 additional fetal losses above expected per 100 pregnancies

Most of the excess fetal losses occurred after gestational week 20,

and nearly half occurred after gestational week 25.

Women vaccinated with dose 3 during weeks 8-13

A higher-than-expected number of fetal losses

Nearly 1.9 additional fetal losses above expected per 100 pregnancies.

In contrast,

Pregnant women vaccinated for influenza during weeks 8-27

Exhibited a consistently lower-than-expected observed number of fetal losses,

likely the result of healthy vaccinee bias.

Women vaccinated for COVID-19 or influenza prior to pregnancy exhibited according-to-expected or lower-than-expected numbers of fetal losses.

Conclusion

Overall, the findings in this paper provided concerning evidence of a higher-than-expected fetal loss rate associated with mRNA COVID-19 vaccine doses received during early pregnancy (gestational weeks 8-13).

The safety signal should be further investigated by regulatory authorities as part of their risk assessment of vaccination during pregnancy with specific focus on the physiological effects in early pregnancy.

There is also a need to conduct pathophysiological studies to better understand the potential biological mechanisms.

Additionally, it would be insightful to assess the potential impact of non-mRNA COVID-19 vaccines.

The findings also underscore the importance of conducting dedicated and statistically powered prospective clinical trials to study the impact of vaccination for COVID-19 and other pathogens during pregnancy to better inform recommendations to this vulnerable population.