Pfizer, Moderna Covid vaccines safe and effective in pregnancy, according to new data

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  • In a new study, the mRNA vaccines by Pfizer-BioNTech and Moderna were found to be safe and effective in pregnant women
  • The results also suggest that vaccine-induced immunity is passed on from mothers to infants
  • However, current studies lack information on the potential risks to the foetus 

The Covid-19 vaccines by Moderna and Pfizer-BioNTech were found to trigger strong immune responses in pregnant and breastfeeding women – equivalent to that of other women of reproductive age, new research revealed.

The study results initially appeared in the preprint server, medRxiv, on 8 March, but was later published in the peer-reviewed journal, the American Journal of Obstetrics and Gynecology (AJOG) on 25 March.  

The authors explained that because pregnant and breastfeeding women were excluded from initial Covid-19 vaccine trials (due to safety concerns), data to guide vaccine decision-making were lacking.

Additional findings from their research indicated that the two vaccines are equally safe in all women of reproductive age, and that they likely offer at least some protection to foetuses through the placenta, as well as to newborns through breast milk.

Both vaccines use messenger RNA (mRNA) technology, a novel vaccine platform never before tested in pregnancy, they wrote, adding: “This study provides the first data from a large cohort on maternal antibody generation in response to Covid-19 vaccination, compares vaccine-generated immunity to that from natural infection in pregnancy, and suggests vaccination of pregnant and lactating women can confer robust maternal and neonatal immunity.”

131 women enrolled

The study enrolled a small group of 131 vaccinated women (primarily healthcare workers) at two academic medical centres between December 2020 and February 2021. 

In this group, 84 women were pregnant; 31 breastfeeding; and 16 of reproductive age (18 to 40 years) but not pregnant. The women provided blood samples at the time they received their first and second jabs, and then again two to six weeks after their second dose.

Participants who gave birth during the study also provided a sample at the time of delivery. All the blood samples were tested for SARS-CoV-2 (the virus that causes Covid disease) antibodies – molecules that bind to the virus and destroy it. 

For comparison, the researchers also assessed banked blood samples from 37 women who were infected with Covid during pregnancy.

The results

They found that vaccine-induced antibodies were equivalent in pregnant and breastfeeding women compared to the non-pregnant women in the group. Of the pregnant participants, 13 gave birth during the study period, which led the researchers to analyse umbilical cord blood from 10 of them. All 10 samples contained vaccine-generated antibodies, suggesting that immune protection against SARS-CoV-2 had passed from the mothers to their infants. 

"Strikingly higher levels of SARS-CoV-2 antibodies were observed in all vaccinated women compared to pregnant women with natural infection," they wrote.

And even more promising was that that the measure of antibodies were significantly higher than those induced by SARS-CoV-2 natural infection (catching the virus itself) during pregnancy. Vaccine-generated antibodies were also present in the breastmilk samples collected after vaccination.

While the second vaccine dose, also known as the "booster" dose, increased SARS-CoV-2-specific IgG (Immunoglobulin G), the case was not the same for IgA (Immunoglobulin A), in the mothers’ blood and breastmilk. They speculate that this may be related to the intramuscular administration of the vaccine. 

IgG is the most common antibody found in our blood and other body fluids. Its role is to protect us against bacterial and viral infections. IgA, which also helps our bodies fight off illness, is an antibody blood protein that forms part of our immune system. 

In cases of natural infection with SARS-CoV-2, the US Centers for Disease Control and Prevention (CDC) notes that IgA antibodies decay more rapidly than IgG, although the clinical significance of IgA in SARS-CoV-2 is not yet established.

Risks to foetus requires further research

“When considering vaccination in pregnancy, evidence regarding maternal and foetal benefit, as well as potential maternal and foetal harm and effects on pregnancy outcomes should be weighed carefully,” cautioned the authors.

While the risk of severe Covid illness is low in pregnant women, pregnancy is a risk factor for severe diseases, they stressed. Existing data, they said, provide a compelling argument that the Covid mRNA vaccines induce similar immunity in pregnant and breastfeeding women as in the non-pregnant population, but these data are not entirely clear on the potential risks to the foetus – something this study didn't assess. 

Therefore, while this new study provides encouraging evidence that the vaccines work well in pregnant women and breastfeeding mothers, the potential risks to the foetus, the study authors wrote, warrants further research.

READ | Two more J&J trials underway to test vaccine in pregnant women and adolescents, and two-dose effect

READ | How Covid vaccines get approved: 4 things you need to know

READ | Pregnant women at increased risk of severe Covid - new study

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