Newborn COVID antibodies are protective proteins infants receive from their mothers, providing defense against the SARS-CoV-2 virus. This phenomenon, known as passive immunity, allows babies to benefit from their mother’s immune response without developing their own antibodies. This temporary shield is particularly important for safeguarding infants who cannot yet be vaccinated.
How Newborns Acquire COVID Antibodies
Newborns primarily acquire COVID antibodies through two main pathways: across the placenta during pregnancy and through breast milk after birth. The transplacental transfer of antibodies is a natural process where the mother’s antibodies cross the placental barrier into the fetal bloodstream. This transfer happens throughout pregnancy, with efficiency increasing as pregnancy progresses, especially during the third trimester.
After birth, breast milk serves as an additional source of antibodies for the newborn. Mothers who have been vaccinated or previously infected with COVID-19 can pass these immune proteins to their infants through breastfeeding. This provides localized protection, particularly for the infant’s mucosal surfaces like the nose and mouth.
Antibody Types and Their Duration
The primary type of antibody transferred from mother to fetus across the placenta is Immunoglobulin G (IgG). IgG antibodies are the most common antibodies found in blood and are responsible for systemic protection against various pathogens. Their presence in umbilical cord blood confirms successful transfer from the mother to the developing baby.
In contrast, Immunoglobulin M (IgM) antibodies in a newborn’s blood indicate the infant has had its own infection, rather than receiving these antibodies from the mother. While breast milk can contain small amounts of IgG and IgM, it is predominantly rich in secretory IgA (SIgA), which offers mucosal immunity. Maternally acquired antibodies are temporary; studies show that IgG antibody levels in infants born to vaccinated mothers can persist for up to six months, with detectable levels in approximately 57% of infants. For infants born to mothers with natural infection, detectable antibody levels at six months are significantly lower, around 8%.
Impact of Maternal Immunity Source
The source of a mother’s immunity, whether from vaccination or natural infection, plays a role in the antibody response and transfer to newborns. Maternal vaccination against COVID-19 during pregnancy is effective in producing robust antibodies that are readily transferred to the newborn. Studies indicate that vaccinated pregnant women can have a significantly greater antibody concentration, sometimes ten-fold higher, compared to those who had a natural infection. Optimizing antibody transfer to the infant appears linked to the timing of vaccination, with studies suggesting that vaccination during the second or third trimester, particularly around 20 to 32 weeks of gestation, leads to peak antibody transfer.
While natural infection during pregnancy also leads to antibody transfer, the levels and breadth of protection can be more variable. Research shows that infants born to mothers who were vaccinated during pregnancy tend to have more persistent anti-spike IgG antibodies compared to those whose mothers had only a natural infection. This suggests that maternal vaccination provides a more consistent and stronger antibody shield for the newborn.
Protection for the Newborn
Maternally acquired antibodies provide newborns with a protective effect against COVID-19, which is especially important as infants under six months of age are not yet eligible for vaccination. These transferred antibodies can reduce the risk of severe illness, hospitalization, and death from COVID-19 in infants. For instance, babies born to mothers who received two doses of an mRNA vaccine during pregnancy were 61% less likely to be hospitalized with COVID-19 in their first six months of life compared to those born to unvaccinated individuals.
Despite the benefits, these maternally derived antibodies do not guarantee complete immunity against COVID-19. The level of protection can vary, and while anti-spike IgG levels correlate with protection from serious illness, the exact antibody titer needed for full protection remains an area of ongoing research. Therefore, other protective measures, such as avoiding exposure to the virus, remain important for newborns.