The question of whether maternal COVID-19 immunity extends to a nursing infant is a major concern for new parents. Antibodies are protective proteins created by the immune system to neutralize threats like the SARS-CoV-2 virus. When a mother is exposed to the virus or receives a vaccine, scientific evidence confirms that a significant portion of this defense can be shared with the baby through breast milk.
Confirmation of Antibody Transfer
Research has definitively established that mothers transfer SARS-CoV-2 antibodies into their breast milk, a finding consistently observed across numerous studies since the start of the pandemic. This transfer occurs whether the mother acquired immunity from a COVID-19 vaccine or from a natural infection. The mechanism is a natural biological function of human lactation, designed to confer immunological protection to the infant. The presence of these active antibodies in breast milk has been shown to neutralize the virus in laboratory settings. This confirmed pathway provides a form of defense for newborns and young infants who are not yet eligible to receive a vaccine themselves.
The Specific Immune Components in Breast Milk
Breast milk is rich in diverse immune components, but the primary antibody transferred against SARS-CoV-2 is Secretory Immunoglobulin A (sIgA). This type of antibody is uniquely suited for mucosal surfaces, forming a protective lining in the infant’s gastrointestinal and respiratory tracts to block pathogens from entering the body. While sIgA is the most abundant antibody, Immunoglobulin G (IgG) is also present in the milk. IgG is the most common antibody found in the bloodstream, and its transfer provides a systemic layer of passive immune protection. Together, these immunoglobulins work to safeguard the infant at the common entry points for the virus.
Comparing Immunity Sources: Vaccination Versus Infection
The type and quantity of antibodies passed through breast milk differ based on how the mother acquired her immunity. Maternal vaccination, particularly with the mRNA vaccines, reliably generates a robust and dominant IgG antibody response in breast milk. This response tends to be more consistent and predictable between individuals than natural immunity. Conversely, mothers who have recovered from a natural COVID-19 infection tend to produce breast milk with a higher level of sIgA antibodies.
Both the IgG-dominant response from vaccination and the IgA-dominant response from infection have shown the capacity to neutralize the SARS-CoV-2 virus. Experts generally advocate for vaccination in breastfeeding mothers because it induces a standardized, high-quality antibody response. Furthermore, receiving a booster dose has been shown to elevate the levels of both IgG and IgA antibodies in breast milk, providing an even stronger defense profile.
What Passive Immunity Means for the Infant
The transfer of antibodies through breast milk provides the infant with what is known as passive immunity. This means the infant receives ready-made defenses rather than having to produce them actively, which is crucial for their underdeveloped immune system. Studies confirm that these antibodies are successfully ingested and pass through the infant’s digestive system, where they can coat the mucosal lining.
This passive protection is temporary, lasting as long as the mother continues to nurse and for a period shortly after. While this immunity does not guarantee the baby will never contract the virus, it is aimed at reducing the severity of illness, lowering the risk of complications, and protecting against hospitalization. The duration of this protection varies; IgA antibodies may persist for up to a year post-infection, while vaccine-induced antibody levels may decline after six months.