Pregnant women who receive a COVID-19 vaccine appear to provide immunity to the mother and the baby against the disease. This is an important reason for women to get the vaccine even if they are pregnant.
Several preliminary studies suggest that pregnant women who receive either the Moderna or Pfizer mRNA vaccine had COVID-19 antibodies in their umbilical cord blood. Furthermore, one of the studies also showed antibodies in breast milk, although this may not be as important as what was detected in the umbilical cord.
This post will examine some of the evidence that supports the fact that the COVID-19 vaccine may confer immunity to the disease for not only the mother but also the baby.
Background on mother-baby immunity
I have previously written about how immunity is transferred, but I want to give a brief summary so that the reader can understand how this works.
In infants, there is a version of the innate immune system called passive immunity. During pregnancy, maternal antibodies produced by the mother’s own adaptive immune system can be transported across the placenta into the fetal blood supply. These antibodies are called immunoglobulin G, or IgG – they are the only one of the five classes of antibodies that can cross the placental barrier.
Immunoglobulin G is the most common class of antibodies in our bodies. They are responsible for protecting us against bacteria and viruses through several biochemical interactions:
- They immobilize and clump together pathogens so that they can be destroyed by certain phagocytic immune cells allowing the body to rid itself of those pathogens.
- They can eliminate pathogens directly,
- They can bind and neutralize toxins produced by pathogens.
- They can directly kill cells.
Upon birth, babies have all the IgG’s that they will ever get from the mother. They will not get any more of them from the mother, including from breastfeeding. And those IgGs do not reproduce themselves or train the baby’s immune system to produce them.
Maternal IgG antibodies are temporary, however, and gradually disappear within about 6-8 months after birth. During those months, the baby begins to develop its own adaptive immune response and produces IgGs in response to pathogenic viruses and bacteria that they encounter. By six months, all of the maternal IgG antibodies are gone, and all of the remaining IgGs are from the baby. During this time, when babies receive vaccines, they begin to produce their own antibodies to those vaccine-preventable diseases.
Furthermore, this is why pregnant women should consider getting important vaccinations, like for pertussis, because they boost the level of these maternal antibodies so that they can be passed to the fetus. And a fully vaccinated mother can protect their newborn against diseases that can be dangerous, even deadly.
And just because I went full science on the reader, I hope it is clear as a fall morning in New England that this is an amazing evolutionary adaptation that protects the newborn baby. And vaccines help the mother then help the baby to protect itself against deadly pathogens, like COVID-19.
COVID-19 vaccines and immunity for the baby – research
Recently published research strongly suggests that pregnant women who have recovered from COVID-19 can pass IgG and IgM antibodies through the umbilical cord to the baby. Of course, if it happens in a “natural immunity,” researchers hypothesized that it should also happen with the COVID-19 vaccines.
This leads to several research initiatives to determine if SARS-CoV-2 antibodies could be detected in the umbilical cord blood and breast milk of women who were vaccinated.
The first study, which was posted as a preprint (see Note 1) studied more than 130 vaccinated women, including 84 who were pregnant and 31 who were lactating. The study found that these women had similar immune responses as found in non-pregnant women, suggesting that the vaccines worked as well in pregnant as nonpregnant women.
The study also showed that all 10 women who went to term and delivered their babies during the study period showed detectable antibodies to SARS-CoV-2 in their cord blood. And they found that all of the lactating women had antibodies in their breast milk.
Interestingly, though it is hard to draw a conclusion from it, one woman who had received only one dose of the vaccine prior to the birth of her baby also had antibodies in the cord blood, but it was lower than those who were fully vaccinated.
Interestingly, the Moderna vaccine group had higher levels of one type of antibody called IgA in breast milk. This antibody is important for the protection of mucosal membranes, which are targeted by SARS-CoV-2, and could help the babies’ protection against the disease.
However, this is a very small sample size, so it’s difficult to state its actual importance. In addition, we don’t know why the Moderna vaccine had such a robust IgA response. And we don’t know if the IgA antibody confers any immunity to the baby, as this is not typically observed with most vaccine immune responses.
Another preprint (again, see Note 1) provided similar results in 20 women who were vaccinated during pregnancy. Again, this is a small study that needs to be duplicated in a much larger size clinical or observational study.
These are both early, and frankly, small, studies that provide important evidence of the possible transfer of immunity from the mother to the baby. Furthermore, we do not have any data on whether this transfer of antibodies actually protect the babies
However, this is how science starts when examining a question, and over time we will get more and more data that can help us understand this better.
For now, given how safe these vaccines are for pregnant women, and that they may provide immunity to the baby, it gives us even more evidence to support giving the COVID-19 vaccine to the mother-to-be.
- Preprints are scientific papers that are generally posted on so-called “pre-print” servers by scientists. They are not peer-reviewed, are not published yet, and may contain errors that are discovered during editing. Preprints have boomed during the COVID-19 pandemic, as scientists are trying to share data as quickly as they can. The largest preprint servers, medRxiv and bioRxiv, host over 14,600 papers. Remember, because they are not peer-reviewed or published, so they may disappear and have no value.
- Flannery DD, Gouma S, Dhudasia MB, Mukhopadhyay S, Pfeifer MR, Woodford EC, Triebwasser JE, Gerber JS, Morris JS, Weirick ME, McAllister CM, Bolton MJ, Arevalo CP, Anderson EM, Goodwin EC, Hensley SE, Puopolo KM. Assessment of Maternal and Neonatal Cord Blood SARS-CoV-2 Antibodies and Placental Transfer Ratios. JAMA Pediatr. 2021 Jan 29:e210038. doi: 10.1001/jamapediatrics.2021.0038. Epub ahead of print. PMID: 33512440; PMCID: PMC7846944.