SARS-CoV-2 prime and booster vaccinations found to improve pregnancy and birth outcomes

In a recent study posted to the medRxiv* preprint server, researchers evaluated the impact of coronavirus disease 2019 (COVID-19) prime vaccination and booster vaccination during pregnancy on maternal and fetal health outcomes.

Study: The effect of COVID-19 vaccination and booster on maternal-fetal outcomes: a retrospective multicenter cohort study. Image Credit: Natalia Deriabina/Shutterstock

Studies have reported that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections during pregnancy have worsened maternal and fetal health outcomes with increased mortality and morbidity from maternal SARS-CoV-2 infections. However, data on the protective role of COVID-19 prime and booster vaccinations during pregnancy are lacking since there have been concerns regarding the potential adverse effects of vaccines on the health of mothers and their fetuses.

About the study

In the present retrospective cohort study, researchers evaluated the immune protection conferred by prime and booster COVID-19 vaccinations during pregnancy for improved pregnancy and birth outcomes.

The multicenter study was conducted on women aged 18 to 45 who delivered at PJSH (providence St. Joseph health, n=86,833) sites in California, Alaska, Oregon, Montana, Texas, Washington, and New Mexico between 26 January 2021 and 11 July 2022. Data were obtained from PJSH electronic health records (EHRs) of all participants with singleton pregnancies and delivery ≥20 weeks post-gestation.

The study participants were categorized based on their status of vaccination during delivery as follows: (i) unvaccinated individuals (n=48,492), (ii) propensity score matched (PSM)-unvaccinated individuals (n=26,790), (iii) prime-vaccinated individuals (n=26,792; double vaccination with Moderna’s messenger ribonucleic acid (mRNA)-1273 or Pfizer-BioNTech’s BNT162b2 ≥2 weeks before delivery), and (iv) booster-vaccinated individuals (n=7,616).

The prime study outcome was the maternal SARS-CoV-2 infection rate. Secondary maternal outcomes were the duration between breakthrough SARS-CoV-2 infection and complete vaccinations, COVID-19-associated hospital admission rates, oxygen supplementation requirements, vasopressor usage, SARS-CoV-2 infection severity, and medications.

Other maternal health outcomes included rates of gestational hypertension, gestational diabetes, and preeclampsia. The secondary birth outcomes assessed were preterm births, stillbirths, gestational age at delivery, rates of low birth weight (below 2500g), and very low birth weight (below 1500g). COVID-19 was diagnosed based on polymerase chain reaction (PCR) reports.


The majority of maternal SARS-CoV-2 infection cases were reported in the unvaccinated cohort and a few individuals who received prime and/or booster vaccinations developed breakthrough SARS-CoV-2 infections before the SARS-CoV-2 Omicron variant became predominant. However, a few cases of maternal SARS-CoV-2 infections were reported among boosted individuals even during Omicron predominance.

A significantly lower number of maternal COVID-19 cases were reported among booster-vaccinated individuals compared to prime-vaccinated individuals and significantly lesser maternal SARS-CoV-2 infections among vaccinated individuals compared to the unvaccinated PSM-matched or unmatched individuals. The vaccinated cohort with maternal SARS-CoV-2 infections during Omicron predominance showed a lower likelihood of seeking emergency care, with a greater likelihood of receiving care in outpatient settings compared to unvaccinated individuals.

The vaccinated cohort showed a significantly lower likelihood of requiring vasopressors and oxygen supplementation than the unvaccinated matched cohort. Significantly lower rates of stillbirths, very low birth weight, and preterm births were reported for vaccinated individuals compared to the unvaccinated cohort. Three COVID-19-associated maternal deaths were reported, all of which were among unvaccinated individuals.

Significantly lower rates of maternal SARS-CoV-2 infections were reported among boosted individuals with a lower likelihood of requiring hospital admissions and a longer duration between complete vaccination and breakthrough SARS-CoV-2 infections compared to prime vaccinated individuals. In addition, birth outcomes such as preterm births, stillbirths, very low birth weights and small gestational age were significantly lower among booster vaccinated individuals than in the prime vaccinated cohort.

Vaccinated individuals showed an increased likelihood of being elder, non-Hispanics or Asians, residing in urban settings, with higher body mass index (BMI) values, insurance, lower socioeconomic vulnerability, negative history of chronic diabetes, gestational diabetes, preterm births, chronic hypertension, low parity, cesarean section delivery and fetus of the male sex. Vaccinated individuals were less likely to smoke or use non-illicit drugs. No significant differences were observed in the rates of severe or non-severe preeclampsia and gestational hypertension between the vaccinated cohort and unvaccinated cohort individuals.

Overall, the study findings showed that COVID-19 vaccinations protect against poor maternal and fetal outcomes and vaccine boosters enhance the immune protection against SARS-CoV-2 infections. Therefore, pregnant women must be prioritized for SARS-CoV-2 prime and booster vaccinations. Further research must be conducted for exploring the immune benefit of fourth COVID-19 vaccinations during pregnancy.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
  • Samantha N. Piekos et al. (2022). The effect of COVID-19 vaccination and booster on maternal-fetal outcomes: a retrospective multicenter cohort study. medRxiv. doi:

Posted in: Medical Science News | Medical Research News | Disease/Infection News

Tags: Birth Weight, Body Mass Index, Cesarean Section, Chronic, Coronavirus, Coronavirus Disease COVID-19, covid-19, Diabetes, Drugs, Gestational Diabetes, Hospital, Maternal Health, Mortality, Omicron, Oxygen, Polymerase, Polymerase Chain Reaction, Pregnancy, Research, Respiratory, Ribonucleic Acid, SARS, SARS-CoV-2, Severe Acute Respiratory, Severe Acute Respiratory Syndrome, Syndrome, Vaccine

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Pooja Toshniwal Paharia

Dr. based clinical-radiological diagnosis and management of oral lesions and conditions and associated maxillofacial disorders.

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