If a woman catches COVID-19 during pregnancy, can her baby get immunity to the virus in the womb? Early data suggests the answer is yes, but many questions remain.
In a new study, published Jan. 29 in the journal Pediatrics JAMA, scientists analyzed blood samples from more than 1,470 pregnant women, 83 of whom tested positive for antibodies to SARS-CoV-2, the coronavirus responsible for COVID-19, at the time of childbirth. Umbilical cord blood samples from most babies born to these women have also tested positive for antibodies, suggesting that the babies have acquired this passive immunity.
The amount of antibodies passed to the baby was highly dependent on the type and amount of antibodies present in the mother and when she contracted COVID-19 during pregnancy.
“The longest [the] the time between maternal infection and childbirth, the greater the transfer of antibodies, ”wrote study authors Dr Karen Puopolo and Dr Scott Hensley of the Perelman School of Medicine. University of Pennsylvania, in an email.
This correlation was maintained if the mother developed symptoms of COVID-19 or remained asymptomatic during her infection.
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The transferred antibodies may provide protection to the newborn, but “ there is still work to be done to determine the levels and types of antibodies needed to protect newborns from infection with SARS-CoV-2, and how long these antibodies can last in the circulation of the newborn. “Says the authors.
Another big question is to what extent the transferred antibodies “neutralize” the coronavirus – that is, block its ability to infect cells, they said.
“It is encouraging to have these data,” said Dr Flor Muñoz-Rivas, associate professor of pediatric infectious diseases at Baylor College of Medicine in Houston, who was not involved in the study.
By studying the transfer of antibodies after natural infection with COVID-19, we can gather clues as to whether vaccines given to pregnant women offer similar protection to newborns, he said.
First results
In the new study, the team specifically tested for antibodies that adhere to the coronavirus spike protein, a structure that protrudes from the surface of the virus; All of the antibodies the team are looking for target the “receptor binding domain” (RBD), the part of the peak that directly binds to the receptor, or gateway, on cells. RBD antibodies are the most critical for neutralizing the coronavirus, Live Science previously reported.
But not all RBD antibodies can cross the placenta, Muñoz-Rivas said. Indeed, the placenta only allows the passage of certain antibodies, by using a special receptor and a protein that transports the antibodies to the organ. Only tiny Y-shaped antibodies called immunoglobulin G (IgG) can enter the receptor, so only they can reach the fetus and provide immune protection, he said.
Not all babies received protection: 72 of 83 babies born to antibody-positive mothers had IgG in their umbilical cord blood, and the overall amount correlated with IgG levels in their mothers’ blood. The remaining 11 babies who tested negative for antibodies did so for two reasons.
Six of the babies’ mothers had relatively low IgG levels, suggesting that they were probably “so early in the infection that they did not have time to produce and transfer antibodies across the placenta. “, said the authors.
Either that or the mothers simply produced fewer antibodies than average, but that’s a less likely scenario, they added. The mothers of the other five babies only tested positive for so-called IgM antibodies, which cannot cross the placenta.
IgM antibodies appear early in an infection and then go away once the infection clears, Muñoz-Rivas said, so the five mothers who only tested positive for IgM were in the early stages of the infection. infection. If IgM antibodies appear in a fetus or newborn baby, this indicates that the fetus has been directly infected with the virus. In this study, no IgM for SARS-CoV-2 was detected in any cord blood sample, which means that no fetus contracted COVID-19 while it was still in the uterus.
However, the study cannot say for sure that SARS-CoV-2 is never transmitted to the fetus before birth, the authors said.
What does this mean for vaccines?
Although the study shows that IgG antibodies can cross the placenta, scientists have yet to determine how well the transferred antibodies protect against infection, the authors said.
Researchers can test how well antibodies block infection by using “neutralization tests,” experiments in which they grow the virus on a plate containing antibodies and human cells, to see if the antibodies prevent infection. . Live Science reported earlier. The authors could also follow babies born with antibodies, to see how long their antibodies persist and if any of the babies contract COVID-19 later, Muñoz-Rivas said.
These types of studies would provide a benchmark of what to expect after a pregnant person contracts COVID-19; the natural immune response could then be compared to what we see in vaccinated mothers and their newborns, Muñoz-Rivas said.
Currently, the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) recommend that only people at high risk of exposure to SARS-CoV-2 or at high risk of disease serious, due to a medical condition, they should consider getting vaccinated during pregnancy and seeing a doctor before receiving one.
Along with other vaccines given during pregnancy, such as those against tetanus and pertussis, antibody levels in the newborn drop rapidly when the baby is two months old, Muñoz-Rivas wrote in an editorial published on the 29th. january in Pediatrics JAMA. This drop then slows down and antibody levels continue to drop steadily for the next four to eight months.
Likewise, for COVID-19 vaccines, the antibodies found in the umbilical cord blood would be the “starting point” or the maximum number of antibodies the baby receives before the levels start to drop, he said. he declares. To maximize the amount of antibodies transmitted to the fetus, mothers may have to wait until the second trimester to be vaccinated; After about 17 weeks of gestation, the placenta grows large enough to pump a significant amount of antibodies to the developing baby, he said.
While it is encouraging that maternal vaccines can offer protection to newborns, “for COVID, the best we know at this time, the goal would be to protect the mother,” Muñoz said. Rivas.
Pregnancy increases the risk of serious illness and death from COVID-19, while the majority of newborns who test positive have had mild or no symptoms and have recovered from the virus. According to the Centers for Disease Control and Prevention. As with influenza infections, mothers appear particularly vulnerable in the third trimester and are more likely to develop serious conditions, such as pneumonia and respiratory failure, if they contract COVID-19 at this stage, Muñoz-Rivas said. .
So the second trimester might be the best time to get the shot, he said. In this way, potential side effects could be avoided during the first trimester, when conditions such as inflammation and fever can disrupt the development of the fetus, while the immune system would still have enough time to speed up its response before. the third trimester. Of course, scientists have yet to conduct observational studies and clinical trials to determine the best time during pregnancy to administer the COVID-19 vaccine, Muñoz-Rivas said.
“If we can, on top of that, protect the baby, that’s an advantage,” he said. That said, given that COVID-19 vaccines won’t be available for babies anytime soon, Muñoz-Rivas said he would see it as a pretty big benefit.
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This article was originally published by Living Science. Read the original article here.
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