The Joint Committee on Vaccination and Immunisation (JCVI) define pregnant women as a clinical risk group within the COVID-19 vaccination programme. Vaccination is the best way to protect against the known risks of COVID-19 in pregnancy for both women and babies, including reducing the risk of admission to intensive care and premature birth.
Evidence on vaccine safety in pregnancy
More than 1.3 million women worldwide have had COVID-19 vaccines in pregnancy. Studies following up nearly 350,000 pregnant women in the US and UK who were vaccinated in pregnancy have not raised any safety concerns.
The UKHSA (formally Public Health England) and Public Health Scotland have reported that well over 150 000 pregnant women have received a COVID-19 vaccine in England and Scotland, with no serious adverse effects recorded. Current research indicates COVID-19 vaccines do not contain ingredients that are known to be harmful to pregnant women or to a developing baby. Studies of the vaccines in animals to look at the effects on pregnancy have shown no evidence that the vaccines cause harm to the pregnancy or to fertility.
As these are new vaccines, there are limited data on the long-term effects on babies born to women who received a COVID-19 vaccination in pregnancy. However, as with other non-live vaccines (such as flu and whooping cough), COVID-19 vaccines cannot cause infection, and these have been given to women in pregnancy for many years without any safety concerns. The mRNA vaccines (Comirnaty/PfizerBioNTech and Moderna Spikevax) are also quickly broken down once they have been injected – within a few days of vaccination there will be no vaccine mRNA left.
According to available data, a pregnant woman who has a COVID-19 vaccine is not at an increased risk of having adverse pregnancy outcomes. Worldwide data, looking at many thousands of people vaccinated in pregnancy, has reported no increased risk of miscarriage, preterm birth or stillbirth following vaccination. Nor does vaccination increase the risk of a small-for-gestational age baby or developing congenital anomalies.
One of these studies, from St George’s, University of London, published in the American Journal of Obstetrics and Gynecology (AJOG), compared pregnancy outcomes for women who had received a COVID-19 vaccine and those who had not. The study found there were no significant differences between the two groups, with no increase in stillbirths or premature births, no anomalies with development and no evidence of babies being smaller or bigger.
More research is being done, monitoring both the mother and baby’s health during pregnancy and for a year after the baby’s birth. We know the COVID-19 vaccines are safe in pregnancy, but this is the next step in looking at the level of protection they provide, what the best interval between doses is, and the immune responses produced in both the mother and baby after vaccination.
Data on rates of miscarriage
Worldwide data shows that the rates of miscarriage were the same in those who had received a COVID-19 vaccine during pregnancy as in the general population who had not been vaccinated. The UK Medicines and Healthcare products Regulatory Agency’s (MHRA) Yellow Card scheme collects and monitors information on safety concerns, such as suspected side-effects or adverse incidents involving medicines and medical devices, including vaccines. They have been analysing reports of miscarriage and stillbirth in pregnant women who have received the COVID-19 vaccines and have not identified any pattern to suggest the COVID-19 vaccines used in the UK, or any reactions to these vaccines, increase the risk of miscarriage or stillbirth.
Possible adverse effects from COVID vaccines
In non-pregnant individuals, the COVID vaccines are known to have mild and short-lasting side-effects, such as a fever or muscle ache lasting a day or two. Reports of serious side-effects, such as allergic reaction or clotting problems, have been very rare.
Regarding serious blood clots, the JCVI has stated that "there are currently no known risk factors for this extremely rare condition, which appears to be an idiosyncratic reaction on first exposure to the Oxford-AstraZeneca COVID-19 vaccine". This means that someone is not necessarily at higher risk of this serious side-effect just because they have a higher risk of other blood clots, for example because they are pregnant. Because this side-effect is so rare, we can't know the exact risk in pregnancy.
This information on the Oxford-AstraZeneca vaccine may be less relevant for pregnant women now that the JCVI recommends offering the Comirnaty/Pfizer BioNTech or Moderna Spikevax vaccines in pregnancy, where available. The government has also advised that individuals under the age of 40 should be offered an alternative vaccine to the Oxford-AstraZeneca vaccine, based on the risk/benefit ratio for this age group.
Pregnant women who have been vaccinated can be monitored by The UK Teratology Information Service (UKTIS).Pregnant women can register directly with the MHRA Yellow Card Vaccine Monitor. Another reporting mechanism for healthcare professionals is the PHE Inadvertent Vaccination in Pregnancy (VIP) system. As of April 2022, pregnancy status is recorded in the national vaccination programme to make sure pregnant women and their babies’ outcomes can be followed up.
COVID-19 vaccine when breastfeeding
In line with UK Government and JCVI advice, the RCOG recommends COVID-19 vaccination to those who are eligible and breastfeeding.
Emerging research raises the possibility that trace amounts of the COVID-19 vaccine can briefly be detected in breastmilk following vaccination. These limited studies have inconsistent results, which should be viewed with caution. No vaccine mRNA has been identified in the babies of breastfeeding women who have been vaccinated. These studies have not affected clinical guidance.