Globally, over 200 million people are pregnant each year. Whether they should be offered the new Covid-19 vaccines as they become available is an important public health policy decision. Whether pregnant people should seek vaccination is a deeply personal decision.
Evidence to date suggests that people who are pregnant face a higher risk of severe disease and death from Covid-19 infection compared to people who are not pregnant. For instance, pregnant people are three times more likely to require admission to intensive care and to need invasive ventilation. The overall risk of death among pregnant people is low, but it is elevated compared to similar people who are not pregnant. Some studies suggest that Covid-19 in pregnancy might be associated with increased rates of preterm birth.
Our understanding of the probability and severity of harms from SARS-CoV-2 infection in pregnancy is evolving. The pandemic has been ongoing for just over a year, which limits what can currently be known about the health risks of Covid-19 disease for pregnant people, and especially their offspring. Whether SARS-CoV-2 infection in pregnancy poses risks to the developing fetus remains underdetermined. Current evidence suggests that transmission of SARS-CoV-2 to the fetus is rare. However, severe maternal illness can have serious implications for the fetus. For example, fevers during early pregnancy have in some studies been associated with increased risk for certain birth defects. Since the pandemic has only been with us for just over a year, there are no data yet on long-term childhood outcomes for offspring exposed in utero.
There are still significant unknowns: How do risks vary by trimester? What are the risks of asymptomatic infection? Further, most current information about Covid-19 disease and pregnancy comes from high-income countries, limiting its global generalizability.
At this point, tens of thousands of pregnant people have received COVID-19 vaccines globally, including in the U.S., Canada, the U.K., and Israel. Thus far, there have been no reports suggestive of concern. Additionally, none of the vaccines that have thus far been authorized for use in the U.S. – the Pfizer-BioNtech, Moderna, and Johnson & Johnson/Janssen vaccines, as well as the AstraZeneca vaccine authorized in other countries – contain live or replication competent viruses. Therefore, it is extremely unlikely that a vaccine virus could replicate, cross the placenta, and infect the fetus. However, more research is needed in order to better characterize the safety profile of each Covid-19 vaccine in pregnancy.
Although there is not yet pregnancy-specific data about Covid-19 vaccines from clinical trials, the vaccines have been studied in pregnant laboratory animals. Called developmental and reproductive toxicity (DART) studies, research with pregnant animals can provide reassurance about moving forward with vaccine research in pregnant people. There are no concerning signals from DART study data for the Pfizer BioNtech, Moderna, Johnson & Johnson/Janssen, and AstraZeneca vaccines. Small numbers of participants in the research trials for these vaccines have become pregnant. No concerning risk signals in those pregnancies have been reported.
All three of these vaccines offer a very high level of protection against serious Covid-19 disease. There is little reason to believe these vaccines will be less effective in pregnant people than they are in people of comparable age who are not pregnant.
The absence of pregnancy-specific data for Covid-19 vaccines has made regulatory and public health decision-making complicated. Largely due to the absence of evidence, most public health agencies have held back on making explicit recommendations on Covid-19 vaccine administration in pregnancy. In the U.S., Canada, the UK, and several other countries, the position of the relevant public health authority is that pregnant people who otherwise qualify for authorized vaccine – such as pregnant people who are health care workers or members of other prioritized essential workforces – should be permitted to make their own decisions about vaccination, based on their assessment of whether the prospect of benefit to them and their offspring outweighs the risks. This is also the position of the World Health Organization (WHO) for the vaccines they have thus far evaluated. In Israel, the Ministry of Health and Vaccines Prioritization Committee recommended vaccination for pregnant people in their second or third trimester. Some jurisdictions in the U.S. are already offering the vaccine to pregnant people given higher Covid-19 risk in pregnancy, including the District of Columbia, Pennsylvania, and Mississippi.
Professional societies, such as the American College of Obstetricians and Gynecologists (ACOG), the Society for Maternal-Fetal-Medicine (SMFM), and the Royal College of Obstetricians and Gynaecologists (RCOG) all support Covid-19 vaccination in pregnancy when the benefits outweigh the risks.
The major benefit of the Pfizer BioNtech, Moderna, Johnson & Johnson/Janssen, and AstraZeneca vaccines to all people, pregnant or not, is that being vaccinated provides a high level of protection against serious Covid-19 disease.
How important the protective benefit of Covid-19 vaccination is to any individual pregnant person depends on how likely they are to get infected, and how likely they are to get seriously ill, if infected. Pregnant people differ in how likely they are to get infected. A person’s risk of becoming infected depends on at least three things: 1) whether their job puts them at risk of infection; 2) the rate of transmission in their community; and 3) who they live with, especially whether they live with people who are at increased risk because of their jobs, or in a crowded home or densely populated neighborhood. For example, people whose jobs require them to be in regular contact with many people are at higher risk of infection than people who can work from home. Similarly, people who live with other people who also work outside the home are at greater risk than people who live alone or only with others who also work or attend school from home.
Pregnant people also differ in how likely they are to get seriously ill with Covid-19 disease, if they become infected. While pregnancy by itself is a risk factor for serious illness, some medical conditions like diabetes, heart disease, or being very overweight are even greater risk factors. People who are pregnant and also have high-risk medical conditions are more likely to develop severe Covid-19 illness if they become infected than pregnant people who do not have relevant medical conditions.
Pregnant people should also consider whether they have access to alternative modes of protection from infection. Questions to ask include: can they take a leave from work or be temporarily transferred to a lower-risk job; do they have access to high quality personal protective equipment; and, if someone in their household gets infected or exposed, is there a way for that person to safely isolate away from others?
Resources, including provider information sheets, conversation guides, and decision aids, have been developed to facilitate the values-driven and context-dependent calculations that pregnant people face in the coming months.
Some people prioritized for vaccination have received Covid-19 vaccines while pregnant, and data about their pregnancies are being collected by public health agencies. Registries are being established in multiple countries to capture the experiences of pregnant people who are receiving Covid-19 vaccines. At least one company, Pfizer BioNTech, has begun a pregnancy-specific trial for their vaccine, which will enroll 4000 pregnant people across nine countries.
The absence of pregnancy-specific data around Covid-19 vaccines continues an unfair pattern in which evidence about safety of new vaccines for pregnant people lags behind. This unfairness is ethically problematic in at least two important ways.
First, people may be denied vaccine, or may face barriers in accessing vaccine, because they are pregnant. Public health agencies globally have struggled to determine the most ethical position regarding whether to allow pregnant people to receive Covid-19 vaccines in the absence of pregnancy-specific data. While there is still limited evidence on the safety of currently authorized vaccines in pregnancy, with high vaccine efficacy, no risk signals from studies in pregnant animals, and few biologically plausible risks, the permissive approach that most health authorities have taken enabling individuals to decide for themselves is ethically appropriate. However, in some settings – whether by policy guidance, local guidelines, or even individual provider reticence – a lack of evidence may mean that pregnant people will face unfair denial of highly effective vaccines from which they stand to benefit.
Second, even when pregnant people are eligible for vaccination, because public health authorities have not explicitly recommended Covid-19 vaccines in pregnancy, the burden of making decisions about vaccination has shifted to pregnant people. Evidence gaps shift the responsibility for associated risk more squarely to pregnant people, where their non-pregnant peers have an evidence base and a public health recommendation to back up their vaccination decision. While endorsement from medical professional societies is helpful, without pregnancy-specific evidence or explicit pregnancy recommendations, there is also the risk that pregnant people’s decisions will be biased by the strong risk distortions that are known to be present in the context of pregnancy.
Hopefully, the evidence necessary for public health agencies to make clear, full-throated recommendations about the use of at least some Covid-19 vaccines in pregnancy will be forthcoming in the coming months. Efforts are underway to encourage developers of vaccines not yet approved for use to move more quickly to conduct studies with pregnant people and otherwise undertake efforts to systematically generate evidence on the safety of their products in pregnancy. We will continue to update this brief, as new data and new policies become available, both for the vaccines discussed here and for additional vaccines that will shortly be evaluated for use in public health programs.