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mRNA in breastmilk. That's okay. And more on COVID19 vaccines and pregnancy
A ridiculous amount of misinformation has recently surfaced online regarding COVID-19 vaccinations, pregnancy, and breastfeeding. This is due to a number of bad players intentionally spreading false information as well as some solid players poorly writing tweets.
Regardless of what you see on social media, it is still strongly recommended that all pregnant and breastfeeding people get the COVID-19 vaccine.
I partnered with Dr. Viki Male, an immunologist and lecturer on pregnancy and reproductive immunology at Imperial College London. She updates a fantastic multi-page document with the latest evidence regarding pregnancy and COVID-19 vaccines. Here are answers to some questions circulating right now.
I am pregnant. What are the risks if I get COVID during pregnancy?
There is evidence that COVID infection increases the risk of miscarriage (here, here), although not all studies have been able to find this (here, here). Preterm birth and stillbirth occur more often in pregnant patients with COVID-19, and their babies are more likely to be admitted to the neonatal unit. Pregnant patients with COVID-19 also more likely to need intensive care than COVID-19 patients who are not pregnant.
Can the COVID-19 vaccine cross the placenta?
One study of 19 people who received the COVID vaccine during pregnancy could not detect any vaccine mRNA or spike protein in placenta or cord blood. Babies of vaccinated mothers do not have any anti-spike IgM (a type of antibody), indicating that the vaccines themselves do not cross the placenta. (You can see the data on this here, here, and here, and an explanation on the interpretation of the studies here).
Is it safe to get the COVID vaccine during pregnancy?
Yes. The safety of COVID vaccination during pregnancy is being monitored in a number of ways:
Passive monitoring systems, such as Yellow Card in the UK and VAERS in the USA, collect information that doctors, patients, and their families report. Neither have detected adverse events occurring more often following COVID vaccination than they normally do in pregnancy.
Twenty-seven studies have been conducted across eight countries and 316,470 people vaccinated during pregnancy and tracked outcomes of pregnancy. None of these studies have found any increased risk of miscarriage, preterm birth, stillbirth, or babies being born smaller than expected or with congenital abnormalities following COVID-19 vaccination. A meta-analysis pooling many of these studies found that COVID vaccination actually reduces the rate of stillbirth by 15%, presumably because it prevents stillbirths that occur because of COVID infection.
Registry studies recruit people at vaccination, track the outcomes of their pregnancies, and compare the outcomes to those we normally see in pregnancy. No registry has found an increase risk of miscarriage, preterm birth, stillbirth, or babies needing intensive care or dying:
In the U.S., V-SAFE examined the outcomes for 5,096 people vaccinated in pregnancy and their babies. The first report found the rates of adverse events were the same as we normally see. A follow-up study looking at outcomes of people vaccinated before 20 weeks of pregnancy found no increased risk of miscarriage following vaccination. A second follow up of 1,634 births found that the rates of adverse events at birth remained normal.
In Canada, the BORN Ontario registry comprises 64,234 people vaccinated during pregnancy and showed no increased risk of stillbirth, preterm birth or babies being smaller than expected for their gestational age (here, here, here and here).
In Scotland, a study looked at 18,399 people vaccinated against COVID during pregnancy and found no increased risk of stillbirth, babies dying shortly after birth, or preterm birth following vaccination.
The Swiss COVI-PREG registry followed 1,012 people vaccinated during pregnancy and found no increased risk of miscarriage, preterm birth, stillbirth, or babies needing intensive care or dying.
A small registry study of 390 people vaccinated during pregnancy in Israel found no increased risk of miscarriage, preterm birth, babies being born smaller than expected or with congenital abnormalities, or needing intensive care.
Will being vaccinated while I am pregnant give my baby any protection against COVID once they are born?
We have many reports showing that antibodies the body makes after vaccination (called IgG) do cross the placenta. Early reports suggest that vaccination in pregnancy is about 61% effective at protecting babies under 6 months old from hospitalization with COVID. Two more recent studies (here, here) found vaccination in pregnancy was 80% and 38% protective against hospitalization with Delta and Omicron, respectively, and 71% and 33% effective at protecting against infection.
I am breastfeeding. Should I get the vaccine if I am offered it?
Yes. There is no known risk associated with non-live vaccines (i.e. mRNA vaccines) while breastfeeding. No safety signals have appeared in breastfeeding people or their babies.
Two studies looking for vaccine mRNA in breast milk have been unable to detect it (here and here). Three studies were able to detect it at very low levels. One study found mRNA at 2 parts per billion in 3 out of 10 milk donors. Another study found mRNA in 4 out of 31 milk donors at a maximum of 0.17 parts per billion, and the third study found mRNA in 3 out of 11 milk donors at a maximum of 0.011 parts per billion. You can read an explanation of what “parts per billion” means here, but the latest study means this is roughly equivalent to a single tear in an Olympic pool. (Note that mRNA is part of our everyday life, outside of vaccines. For example, it’s in meat we eat, and our stomach acid is strong enough to break it down.)
A study that looked for the chemical PEG, which is used to stabilize mRNA vaccines, in the breast milk of 13 people found that levels did not increase after vaccination. (Note that PEG is commonly found in many cosmetics, so was found in some milk samples from unvaccinated donors.)
Together, this means those who are breastfeeding do not need to “pump and dump” within 48 hours of vaccination.
A number of studies have shown antibodies get into breast milk at high concentrations. You can find them summarized in this systematic review. One of these studies found that antibodies could persist in breast milk for as long as 6 months after vaccination. There is also some evidence that T cells that respond to COVID-19 get into breast milk (here, here). These antibodies and T cells give your baby some protection against COVID19, although more research is being done to confirm this.
For questions about COVID-19 vaccine safety before pregnancy, including questions about fertility and menstrual cycles, and answers to more questions about vaccines during and after pregnancy, be sure to check out this live document on the latest evidence. It’s updated in almost real time.
The vaccines are safe and effective before pregnancy, during pregnancy, and after pregnancy. For both the parent and the baby. The new bivalent vaccine does not change this. Be sure to get your vaccine!
Love, YLE and Dr. Viki Male
Viki Male, PhD, is faculty of Medicine, Department of Metabolism, Digestion and Reproduction at Imperial College London and holds the Borne-funded Lectureship in Reproductive Immunology. During the pandemic, she has been involved in collating and communicating information on the effect of SARS-CoV2 infection and COVID vaccination on fertility, pregnancy, and breastfeeding, and in research on how COVID vaccination affects the menstrual cycle.
“Your Local Epidemiologist (YLE)” is written by Dr. Katelyn Jetelina, MPH PhD—an epidemiologist, biostatistician, wife, and mom of two little girls. During the day she works at a nonpartisan health policy think tank, and at night she writes this newsletter. Her main goal is to “translate” the ever-evolving public health science so that people will be well equipped to make evidence-based decisions. This newsletter is free thanks to the generous support of fellow YLE community members.