The safety of the COVID-19 vaccine for lactating individuals and their infants was initially uncertain because clinical trials did not include breastfeeding mothers. Since then, extensive real-world evidence and targeted studies have established a clear consensus regarding the safety and benefit of vaccination during lactation. This article addresses the primary questions surrounding the COVID-19 vaccine, its components, the resulting immunity, and practical considerations for nursing mothers. Current information strongly supports vaccination as a protective measure for both the lactating parent and the breastfed child.
Vaccine Components and Infant Safety
The main concern for many nursing parents revolves around whether the vaccine’s active components, such as messenger RNA (mRNA), can transfer into breast milk and affect the infant. The mechanism of action for the mRNA vaccines, like those from Pfizer and Moderna, involves the injection of a genetic instruction encased in a lipid nanoparticle. Once injected into the deltoid muscle, the vaccine material is quickly taken up by local cells to produce the harmless spike protein, which triggers an immune response.
The mRNA is rapidly degraded and does not enter the cell’s nucleus, meaning it cannot alter a person’s DNA. Studies have investigated the presence of the vaccine’s mRNA in expressed breast milk (EBM) following maternal vaccination. While some research initially reported no detectable mRNA, more sensitive studies have occasionally found trace amounts of the vaccine mRNA in EBM, particularly within the first 48 hours post-vaccination.
These trace quantities are considered biologically insignificant for the infant. The mRNA is a fragile molecule that would be further degraded by the baby’s digestive system, making it highly unlikely to be absorbed intact or to cause any effect. The consensus among medical experts is that the minute, sporadic presence of vaccine mRNA does not pose a known risk to the nursing infant. This safety profile reinforces the recommendation that lactating individuals should not interrupt or discontinue breastfeeding after receiving the COVID-19 vaccine.
Passive Immunity Through Breast Milk
The beneficial effect of maternal vaccination is the transfer of protective antibodies into breast milk, a process known as passive immunity. After a lactating individual receives the vaccine, their immune system produces two main types of antibodies against the SARS-CoV-2 spike protein: Immunoglobulin A (IgA) and Immunoglobulin G (IgG). These antibodies are then actively transported into the breast milk.
IgA antibodies are typically found in high concentrations in mucosal secretions, including breast milk, and offer localized protection on the surfaces of the infant’s respiratory and gastrointestinal tracts. IgG antibodies, which are the most abundant type in the blood, also transfer into the milk, often showing a significant increase after the second vaccine dose. Studies have shown that breast milk from vaccinated mothers contains these specific antibodies for up to several weeks after vaccination.
These antibodies are functional, meaning they have the capacity to neutralize the SARS-CoV-2 virus, which could potentially offer the baby some protection against infection or severe disease. While this passive immunity is not a substitute for infant vaccination, it provides a valuable layer of defense for infants who are too young to be vaccinated themselves. The robust antibody response in the milk of vaccinated mothers provides a distinct benefit that outweighs the theoretical, unproven risks of vaccine component transfer.
Guidance from Health Organizations
Major global and national health organizations have consistently issued clear recommendations regarding COVID-19 vaccination during lactation. The Centers for Disease Control and Prevention (CDC), the World Health Organization (WHO), and the American College of Obstetricians and Gynecologists (ACOG) all recommend that lactating individuals receive and stay up to date with the COVID-19 vaccine. These organizations emphasize that the benefits of vaccination for both the parent and the child substantially outweigh any theoretical risks.
ACOG advises that COVID-19 vaccines should not be withheld from lactating individuals who otherwise meet the criteria for vaccination. This guidance stems from the fact that lactating people are at a higher risk of severe illness, hospitalization, and complications from COVID-19 compared to non-pregnant peers. There is no reason to postpone vaccination or a booster dose at any point during the lactation period.
The consensus is built on the understanding that the vaccine cannot cause infection in the mother or the child and that the transfer of protective antibodies is an added benefit. The CDC explicitly states there is no evidence to suggest that COVID-19 vaccines are harmful to either breastfeeding women or their babies. Lactating individuals are encouraged to continue nursing without interruption after vaccination.
Maternal Side Effects and Milk Production
Lactating individuals experience similar short-term side effects after vaccination as the general population, which are typically mild to moderate. The most commonly reported symptoms include pain at the injection site, fatigue, headache, muscle aches, and low-grade fever. These systemic side effects are usually more pronounced after the second dose of the vaccine and generally resolve within 48 to 72 hours.
A specific concern among nursing parents is a temporary change in milk supply. Some studies have noted that a small percentage of lactating individuals (between five and seven percent) reported a temporary reduction in milk supply within the first day or two following vaccination. Possible reasons for this transient effect include decreased feeding frequency due to maternal fatigue or fever, or physiological changes related to the immune response.
This reported reduction in supply is not considered a long-term effect, and milk production typically returns to normal within a few days. Lactating individuals are advised to manage fever with acetaminophen, stay well-hydrated, and continue to nurse or express milk frequently to maintain their supply. There is no evidence that the vaccine affects the long-term composition of breast milk beyond the beneficial addition of SARS-CoV-2 antibodies.