Studies have shown that SARS-CoV-2 generally does not cross the placental barrier to reach the baby who is in the mother’s womb. But this is not the case for antibodies. These can indeed pass from mother to child via the umbilical cord, but they can also be transferred through breast milk after the baby is born. This is why pregnant women in many countries get vaccinated against influenza and whooping cough.
This transfer of antibodies between mother and child is called passive immunity and this process remains valid even for Covid-19. Antibodies specific to the coronavirus have been found in the blood of the umbilical cord in women who have contracted the disease or who have been vaccinated during their pregnancy.
This transfer should ensure better protection of newborns against Covid-19 during their first months of life.
The course of the study
Between July 2021 and January 2022, a study was carried out on 379 babies under six months old admitted to hospital. The babies were divided into two groups. The first group was made up of babies hospitalized because they had symptoms of Covid-19 and tested positive. The second consisted of babies who tested negative but showed suspicious signs.
We are talking here about what is called a “case-control” study. The vaccination status of the mothers was compared for the two groups to see if babies with Covid-19 were more likely to have unvaccinated mothers. All of the babies studied had either an unvaccinated mother or a mother who received two doses of an mRNA vaccine.
According to the results, only 16% of babies with Covid-19 had a vaccinated mother. For infants who tested negative, this figure was 32%, a significant difference according to scientists, and which suggests a protective effect.
The researchers also wanted to know if the timing of the injection of the second dose during pregnancy had an effect on the protection received by the baby. The results suggested that receiving the second dose in the second half of pregnancy offered better protection. However, the study could not really prove this because of a statistical weakness.
Despite these results, the study is still limited for several reasons. There is, for example, the fact that other factors could also have influenced the results: had the mother previously been infected with Covid-19? Or is the baby breastfed?
Further research is also needed to know the duration of this immunity. However, it has been shown by a previous study that an infant whose mother contracted Covid-19 during pregnancy had immunity lasting up to 6 months. It is probable that the vaccination of the mother offers the same protection for at least the same period.
The importance of vaccination in pregnant women
Although Covid-19 has more serious effects on the elderly, it is essential to protect newborns. Scientists have shown that 21% of infants under three months who contracted Covid-19 could be admitted to intensive care. Symptoms generally observed are fever and decreased appetite. For moderate to severe forms, babies may show respiratory symptoms.
By reducing the risk of infection with the virus after birth, maternal vaccination seems to reduce the risk of the child developing these symptoms. Vaccination of the mother during pregnancy also reduces the risk of contracting the disease for the mother and protects her child from the risks of stillbirth, preeclampsia or premature delivery. The vaccine against Covid-19 is also safe during pregnancy, whether for the mother or the child.