Study finds benefits of COVID vaccination in pregnancy outweighs risks

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The coronavirus disease 2019 (COVID-19) pandemic increased global morbidity and mortality exponentially over the course of the last two years, with more than five million deaths reported globally during this period. A new "article in press" explores the efficacy of vaccination against infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in pregnancy.

Study: COVID-19 Vaccination in Pregnancy—Number Needed To Vaccinate To Avoid Harm. Image Credit: Marina Demidiuk /


While causing asymptomatic or mild infection for most individuals, SARS-CoV-2 hits some patients rapidly and hard, with death occurring within a few days of diagnosis in a significant though a small minority of COVID-19 patients. Among the known risk factors for severe COVID-19 are obesity, hypertension, type 2 diabetes mellitus, and lung disease.

Pregnancy has been identified as another high-risk condition for COVID-19. Pregnant women are considered to be more prone to develop severe illness and have complicated pregnancies when infected with SARS-CoV-2. While COVID-19 early in pregnancy may lead to miscarriages, its presence in the third trimester could cause preterm labor, hypertensive disorders, and growth restriction.

Since several COVID-19 vaccines are safely administered in pregnancy without evidence of, or theoretical support for, any injury to the fetus, COVID-19 vaccination in pregnancy is expected to be similarly effective and safe as in non-pregnant women. However, experimental proof is lacking. Pregnant women were excluded from most of the clinical trials that were conducted prior to the approval of the currently available vaccines.

Notably, animal studies have not shown any adverse effect of current COVID-19 vaccines on reproduction. Post-marketing surveillance of humans who have received the vaccine during pregnancy has also not shown any increase in adverse effects above the baseline.

Yet, with significant disagreement even among doctors, there was controversy about whether to administer the COVID-19 vaccine in pregnancy. Even now, many pregnant women are unwilling to get the shot until after their delivery.

In order to arrive at a sound decision, it is necessary to understand both the benefits and the costs of this intervention. Especially when appraising the value of the COVID-19 vaccine in pregnancy, it is essential to remember that the risk of severe illness and complications differ by geographical region and ethnicity, as well.

Moreover, different SARS-CoV-2 variants pose varying levels of risk that can differ with each term of pregnancy In the current The Lancet Infectious Disease study, the researchers calculated the number needed to vaccinate (NNV).

Study findings

In pregnancy, NNV is a useful measure that refers to the number of pregnant women who must be vaccinated in order to prevent harm to the mother and fetus. A NNV value following vaccination must be lower than the NNV that results in harm should vaccination in pregnancy in order to be considered a recommended measure.

In numerical terms, the NNV against any infection with the virus during pregnancy is 11; however, to avert symptomatic COVID-19 during this period, it is greater than 200. Similarly, anywhere from 400-2,000 pregnant women must be vaccinated to prevent one case of severe maternal COVID-19.

Up to 6,800 pregnant women must be vaccinated to avoid having to put one woman on mechanical ventilation. The NNV to prevent fetal harm due to pregnancy complications is 200 for preterm or Cesarean section. However, to guard against one child with neonatal problems, more than 460 pregnant women must get the vaccine.

To help avert growth restriction or stillbirth, thousands upon thousands will require vaccination. However, it should be noted that in real life, the estimated NNV is probably lower than these figures.

This is largely because the incidence of SARS-CoV-2 infection is rising, particularly among the unvaccinated. SARS-CoV-2 variants of concern are also rising in prevalence. Pregnant women often take care of or live with young children, who are typically unvaccinated and interact with others at daycare facilities or during other activities.

Given the absence of systemic inflammation and side effects, current COVID-19 vaccines are not likely to be associated with any serious adverse reactions, making them highly comparable to other vaccines given outside pregnancy. Several rumors, such as a high incidence of myocarditis among vaccine recipients, have been reported; therefore, it should be emphasized that myocarditis occurs once in 37,000 vaccine recipients.

Moreover, with viral vector vaccines, the risk of thrombosis accompanied by thrombocytopenia is one in 50,000 vaccine recipients. Pregnancy complications following the vaccine have not been reported so far, which is an important advantage.


The balance of risk favors COVID-19 vaccination in pregnancy, particularly to avoid severe maternal infection or preterm or cesarean birth. These data should be used to address and avoid vaccine hesitancy driven by knowledge gaps.”

Journal reference:
Dr. Liji Thomas

Written by

Dr. Liji Thomas

Dr. Liji Thomas is an OB-GYN, who graduated from the Government Medical College, University of Calicut, Kerala, in 2001. Liji practiced as a full-time consultant in obstetrics/gynecology in a private hospital for a few years following her graduation. She has counseled hundreds of patients facing issues from pregnancy-related problems and infertility, and has been in charge of over 2,000 deliveries, striving always to achieve a normal delivery rather than operative.


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