The COVID-19 pandemic introduced many questions for new and expectant parents, particularly concerning the safety and protective benefits of breastfeeding. Human milk is recognized as a complex biological fluid that transfers crucial immune factors from mother to infant, offering protection against various pathogens. Following maternal exposure to SARS-CoV-2, either through natural infection or vaccination, specific antibodies are generated and secreted into the milk. This process provides a layer of passive immunity for the baby, leading to the central question of how long this specific defense against the coronavirus remains active in breastmilk.
The Mechanism of Antibody Transfer
The transfer of immune protection begins when a mother encounters a pathogen or receives a vaccine. Specialized immune cells called B cells are activated and travel to the mammary glands. There, they differentiate into plasma cells that produce antibodies tailored to the specific threat.
The dominant antibody found in human milk is Secretory Immunoglobulin A (sIgA), which makes up 80% to 90% of the total immunoglobulins. This antibody is uniquely structured to resist digestion in the infant’s stomach, allowing it to coat the mucosal surfaces of the gut and respiratory tract. A smaller fraction of Immunoglobulin G (IgG) and Immunoglobulin M (IgM) antibodies are also transferred into the milk.
This localized delivery mechanism means the antibodies work directly at the entry points for viruses and bacteria, preventing them from attaching to the infant’s cells. The transfer of these protective factors is independent of the antibodies that cross the placenta during pregnancy, offering continuous mucosal protection throughout nursing.
The Duration of COVID Antibodies in Breastmilk
The persistence of COVID-19 antibodies in breastmilk varies depending on whether the mother developed immunity from a vaccine or from a natural infection. Following maternal mRNA vaccination, anti-SARS-CoV-2 antibodies typically reach their highest concentration in breastmilk within two to four weeks after the second dose. These levels then experience a gradual decline over several months.
Research has indicated that vaccine-induced antibodies can remain detectable in breastmilk for at least six months following the full primary series. The antibodies generated after vaccination are a combination of IgA and IgG, with IgG often being more prominent in the milk response.
In contrast, antibodies generated following a natural SARS-CoV-2 infection tend to be dominated by Secretory IgA. Studies have found that these infection-induced, neutralizing IgA antibodies can persist in breastmilk for an extended period, in some cases up to 10 months. The concentration of antibodies is also influenced by the individual’s immune response, the specific viral variant, and the timing of booster doses.
Protection Provided Through Passive Immunity
The antibodies transferred through breastmilk confer passive immunity, meaning the infant receives the protective factors directly. This protection is immediate. The antibodies work by binding to the SARS-CoV-2 spike protein, which effectively neutralizes the virus and prevents it from infecting the infant’s cells.
The primary protection comes from the sIgA, which acts within the infant’s gut and respiratory system, forming a localized barrier against the virus. By neutralizing the virus at the point of entry, these antibodies can reduce the risk of the infant acquiring the infection.
Even if a breastfed infant does contract COVID-19, the passive transfer of antibodies is thought to decrease the severity of the illness. This reduction in symptom severity is a significant benefit, especially for newborns and young infants who are at a higher risk for severe disease and hospitalization.
Official Recommendations for Breastfeeding
Public health organizations, including the Centers for Disease Control and Prevention (CDC), recommend that breastfeeding individuals receive and stay up to date with COVID-19 vaccinations. Vaccines are considered safe for both the parent and the child, and the transferred antibodies offer a protective benefit to the baby.
Guidance consistently advises mothers to continue breastfeeding even if they contract COVID-19. Studies indicate that breastmilk is not a source of viral transmission, and the benefits of providing immune factors and nutrition outweigh any theoretical risk. When a mother is ill, her body produces a specific antibody response that is transferred to the infant through the milk.
Mothers who are suspected or confirmed to have COVID-19 are advised to take hygiene precautions. These include wearing a mask while nursing and practicing hand hygiene.