Expert Commentary

COVID-19 vaccines during pregnancy: What research shows

We've summarized several academic papers that investigate outcomes of COVID-19 -- and the vaccines against it -- among pregnant individuals.

pregnancy and COVID-19 vaccines
Sandra Murray-Campbell, licensed practical nurse, administers the COVID-19 vaccine to Cpt. Bryana Fournier, a registered nurse for the Bayne-Jones Army Community Hospital emergency department on Jan. 7, at the Joint Readiness Training Center and Fort Polk, La. (Photo by Jean Graves, Department of Defense.)

On Aug. 11, the Centers for Disease Control and Prevention recommended the COVID-19 vaccine for all people 12 years and older, including pregnant people, saying there’s no evidence that the vaccine leads to fertility problems, miscarriage or other health issues.

“The vaccines are safe and effective, and it has never been more urgent to increase vaccinations as we face the highly transmissible Delta variant and see severe outcomes from COVID-19 among unvaccinated pregnant people,” said CDC Director Dr. Rochelle Walensky in a news release.

The federal agency’s endorsement follows an increase in the number of infections among pregnant individuals in recent weeks.

As of Aug. 9, more than 105,600 pregnant people in the U.S. had been diagnosed with COVID-19 and 124 have died since the pandemic started, according to the latest available data from the CDC, which is updated weekly. That’s nearly twice as many infections and deaths reported in January.

CDC officials say the increase is fueled by the circulation of the highly-contagious Delta variant and the low vaccine uptake among pregnant people. As of Aug. 7, 23.2% of pregnant people in the U.S. had received at least one dose of a COVID-19 vaccine, CDC data show. That’s compared with 71% of all U.S. adults 18 years and older.

The agency isn’t alone in recommending the vaccine. The American College of Obstetricians and Gynecologists, or ACOG, and the Society for Maternal-Fetal Medicine — the two leading groups in the U.S. representing specialists providing health care for women — issued a joint statement in July, recommending that all pregnant people get vaccinated against COVID-19.

The World Health Organization recommends pregnant women get COVID-19 vaccines in consultation with their health-care provider. Also, in an interim guidance published in June, it recommends vaccination in pregnant women when the benefits outweigh potential risk, particularly for women who are at a high risk of exposure to COVID-19 and those whose comorbidities put them at a higher risk of developing severe COVID-19.

Even though the overall risk for severe COVID-19 infection remains low, studies have shown that pregnant people are at an increased risk for severe illness from COVID-19 compared with those who are not pregnant.

Underlying medical conditions such as asthma, diabetes, heart disease and obesity can increase the risk of complications even more for pregnant people. Pregnant individuals of color face higher risk of severe illness from COVID-19 due to persisting racial inequalities in the U.S., the CDC says.

In addition, pregnant people who were infected with COVID-19 during the third trimester are at an increased risk of having a preterm birth, which is delivery earlier than 37 weeks, compared with pregnant women who aren’t infected with the virus, according to a CDC study.

Studies are still underway and long-term safety data aren’t available yet, but relying on a growing body of evidence, the CDC says that at this point the benefits of receiving a COVID-19 vaccine outweigh any potential risks of vaccination during pregnancy.

But belief in misinformation continues to hamper vaccination efforts. A national survey by The COVID States Project, conducted between June and July, finds that 11% of Americans believe that COVID-19 vaccines can cause infertility, even though the claim has been debunked. About 20% of Americans also falsely believe that COVID-19 vaccines will alter people’s DNA, contain microchips to track people or contain the lung tissue of aborted fetuses, the survey shows. The COVID States Project was launched in March 2020 by a multi-university group of researchers, focusing on social behaviors and the impact of messaging on the pandemic.

In addition, pregnant people were excluded from the initial COVID-19 vaccine clinical trials, which also may have fueled vaccine hesitancy sentiments. Some COVID-19 vaccine makers have since planned to enroll pregnant people in their clinical trials.

We have summarized several academic papers that investigate outcomes of COVID-19 infection — and the vaccines against it — among pregnant individuals, to help journalists bolster their reporting with data. Please note that while the studies in this roundup have undergone the peer review process, the findings from most are still from a limited time frame, given that the pandemic arrived less than two years ago and the vaccines became available to the public less than a year ago. Periodically, we’ll update this roundup with new studies as new information comes to light.

Pregnant women with COVID-19, United States, January 22, 2020 – August 9, 2021. Source: CDC.

Characteristics and Outcomes of Women With COVID-19 Giving Birth at US Academic Centers During the COVID-19 Pandemic
Justine Chinn; et al. JAMA Network Open, August 2021.

The study shows that pregnant women with COVID-19 had higher rates of preterm birth, ICU admission, respiratory failure requiring intubation, and death compared with pregnant women who didn’t have COVID-19.

Using a large national database without patient-identifying information, researchers looked at records for 869,079 women who gave birth at 499 U.S. medical centers between March 2020 and February 2021. Of those, 18,715 (2.2%) had COVID-19.

Researchers didn’t control for confounders like age, race and co-morbidities such as obesity when calculating outcomes.

The study finds that pregnant women with COVID-19 had a higher risk of preterm delivery — 16.4% versus 11.5%. That’s an increased risk of 42%.

The comparison of pregnant women with and without COVID-19 also shows that those with the infection were nearly six times more likely to be admitted to the ICU, 14 times more likely to require mechanical ventilation, and 15 more times likely to die in the hospital.

It’s important to note the risk of ICU admission, mechanical ventilation and death were still low in each group, relative to the total number of women in the sample. For instance, of the 18,715 pregnant women with COVID-19, 24 died. That’s about 13 deaths in 10,000. For pregnant women without COVID, there were 71 deaths in 850,364, or about 8 deaths in 10,000.

Researchers add that pregnant individuals with COVID-19 were more likely to be Hispanic or Black.

“This information is critically important given the ongoing issues surrounding health care disparities and race,” the authors write in the study. “When considering mortality during childbirth, it is important to understand that racial disparities have been well established preceding the COVID-19 pandemic; however, they have likely been augmented by the pandemic.”

They found no significant increase in C-sections among pregnant women with and without COVID-19.

Source: CDC.

Preliminary Findings of mRNA Covid-19 Vaccine Safety in Pregnant Persons
Dr. Tom Shimabukuro; et al. The New England Journal of Medicine, June 2021.

In this study, the authors use data from three U.S. vaccine monitoring systems and find no safety concerns among pregnant individuals who received COVID-19 vaccines manufactured by Pfizer-BioNTech and Moderna, both of which are based on mRNA technology.

Researchers look at data for 35,691 pregnant individuals, using the V-safe Surveillance System and Pregnancy Registry, a new CDC smartphone-based surveillance app developed for the COVID-19 vaccination program, the V-safe Pregnancy Registry and the national Vaccine Adverse Event Reporting System, or VARES, between December 2020 and February 2021. They compared the data with published studies of pregnant populations before the pandemic.

They find that pregnant individuals didn’t report having any more severe reactions to the COVID-19 vaccines compared with women who were not pregnant — except for nausea and vomiting, which were reported slightly more frequently among vaccinated pregnant individuals after the second dose of the vaccine. Researchers also report similar pregnancy outcomes, including for preterm birth. No newborns, regardless of whether their mothers had received the COVID-19 vaccine, had birth defects.

The authors note that the registry data are preliminary and from a relatively small sample, describing pregnancy outcomes primarily from women who were vaccinated during the third trimester of pregnancy. Long-term studies with large numbers of women vaccinated earlier in pregnancy is needed to assess outcomes, the authors write.

They point out that the vaccines not only protect pregnant individuals from a severe COVID-19 infection, they may also provide some level of protection in newborn babies, although there’s a need for more research.

Update: Characteristics of Symptomatic Women of Reproductive Age with Laboratory-Confirmed SARS-CoV-2 Infection by Pregnancy Status — United States, January 22–October 3, 2020
Laura Zambrano; et al. CDC’s Morbidity and Mortality Weekly Report, November 2020

This study compares COVID-19 infection in women who are and aren’t pregnant, finding that pregnant women with COVID-19 are at a higher risk for severe health outcomes.

Researchers use data from the CDC’s National Notifiable Diseases Surveillance System for 409,462 women who had COVID-19 symptoms between January and October 2020. About 6%, or 23,434, of the study population were pregnant.

The authors adjusted for age, race and ethnicity and underlying medical conditions.

Their analysis shows that pregnant women with COVID-19 had three times the risk of being admitted to the ICU and requiring intubation, compared with women who were diagnosed with the infection but were not pregnant. They also had a 2.4 times higher risk of requiring extracorporeal membrane oxygenation, or ECMO, which is a heart-lung machine used in critically-ill patients. The pregnant women had a 70% increased risk of death.

Source: CDC.

Risk Factors for Illness Severity Among Pregnant Women With Confirmed Severe Acute Respiratory Syndrome Coronavirus 2 Infection — Surveillance for Emerging Threats to Mothers and Babies Network, 22 State, Local, and Territorial Health Departments, 29 March 2020-5 March 2021
Dr. Romeo Galang; et al. Clinical Infectious Diseases, July 2021.

The aim of this study is to determine the risk factors associated with developing severe COVID-19 illness in pregnant women.

The authors used the CDC’s Surveillance for Emerging Threats to Mothers and Babies Network, or SET-NET, which collects information on pregnant individuals and their children for the first three years of their life from 31 state, local and territorial health departments in the U.S. They analyze data for 7,950 pregnant women who had a COVID-19 infection between March 2020 and March 2021.

They find that severe illness from COVID-19 in pregnant women is associated with being 25 years or older, having a job in the health care profession, obesity, chronic lung disease, chronic high blood pressure and diabetes. The severity of the COVID-related illness increased with the number of underlying medical conditions.

Having any underlying medical condition such as asthma or diabetes was associated with a 39% increased risk of severe or critical COVID-19 illness in pregnant women, while having three or more underlying conditions was associated with more than twice the risk, when compared with pregnant women who didn’t have any underlying medical conditions.

The authors note that the findings on risk factors are similar to what’s observed among nonpregnant adults.

“These data can help counsel pregnant women about their risk for moderate-to-severe or critical COVID-19 illness and guide their choice of prevention strategies, target public health messaging, and inform decisions around resource allocation,” the authors write.

The Coronavirus Disease 2019 Vaccine in Pregnancy: Risks, Benefits, and Recommendations
Dr. Irene Stafford, Dr. Jacqueline Parchem and Dr. Baha Sibai. American Journal of Obstetrics and Gynecology, January 2021.

This study stands out because the authors look back at history to show that this is not the first pandemic to pose a higher risk of severe disease for pregnant individuals.

During the 2002 Severe Acute Respiratory Syndrome, or SARS, pandemic, 25% of infected pregnant women died and 57% had miscarriages, the authors write.

Meanwhile, studies of the 2009 H1N1 flu pandemic have shown higher rates of ICU admission and death among infected pregnant individuals than those who were not pregnant, they add.

The authors add that even though pregnant individuals were excluded from the initial mRNA COVID-19 vaccine trials, so far there’s no evidence that the vaccines pose a risk to them or their babies.

Also of note

Short-term Reactions Among Pregnant and Lactating Individuals in the First Wave of the COVID-19 Vaccine Rollout
Dr. Alisa Kachikis; et al. JAMA Network Open, August 2021

This study is based on the first wave of vaccinations in the U.S. in March 2021. Researchers use data from the University of Washington COVID-19 Vaccine in Pregnancy and Lactation Registry to compare the experiences of COVID-19 vaccination among pregnant and lactating individuals with those who were neither pregnant nor lactating, but were planning pregnancy. The majority of the 17,525 participants were health-care workers and white. Researchers find that COVID-19 vaccines were well-tolerated among the three groups. Several study authors reported receiving grants from drug-makers including Merck, Pfizer and GlaxoSmithKline, but not for this published study.

The Impact of COVID-19 on Pregnancy Outcomes: A Systematic Review and Meta-Analysis
Shu Qin Wei, Marianne Bilodeau-Bertrand, Shiliang Liu and Nathalie Auger. Canadian Medical Association Journal, April 2021.

This study looks at 42 international studies involving a combined 438,548 pregnant people. It finds that COVID-19 during pregnancy was associated with an 82% increased risk of preterm birth and a 33% increased risk of preeclampsia, which is a complication of high blood pressure, compared with no COVID-19 during pregnancy. The infection was also associated with a two-fold increase in the risk of stillbirth.

The Differences in Clinical Presentation, Management, and Prognosis of Laboratory-Confirmed COVID-19 between Pregnant and Non-Pregnant Women: A Systematic Review and Meta-Analysis
Durray Shahwar A. Khan; et al. International Journal of Environmental Research and Public Health, May 2021.

This study shows that pregnant women with COVID-19 had twice the risk of ICU admission and requiring mechanical ventilation compared with pregnant women who didn’t have COVID-19.

More information and data sources