Detection of SARS-CoV-2–Specific Antibodies in Human Breast Milk and Their Neutralizing Capacity after COVID-19 Vaccination: A Systematic Review

SARS-CoV-2 is the virus that causes the infectious disease known as Corona Virus Disease 2019 (COVID-19). The severe impact of the virus on humans is undeniable, which is why effective vaccines were highly anticipated. As of 12 January 2022, nine vaccines have obtained Emergency Use Listing by the World Health Organization (WHO), and four of these are approved or authorized by the Centers for Disease Control and Prevention (CDC) in the United States. The initial clinical trials studying COVID-19 vaccine efficacy excluded pregnant and lactating individuals, meaning that data on the effects of the vaccine on breast milk were lacking. Until today, none of the authorized vaccines have been approved for use in individuals under six months. During the first months of life, babies do not produce their own antibodies; therefore, antibodies contained in their mothers’ breastmilk are a critical protective mechanism. Several studies have shown the presence of SARS-CoV-2 antibodies in the breast milk of women who have been vaccinated or had been naturally infected. However, whether these are protective is still unclear. Additionally, research on the BNT162b2 mRNA vaccine developed by Pfizer-BioNTech and the mRNA-1273 vaccine developed by Moderna suggests that these vaccines do not release significant amounts, if any, of mRNA into breast milk. Hence, there is no evidence that vaccination of the mother poses any risk to the breastfed infant, while the antibodies present in breast milk may offer protection against the virus. The primary objective of this systematic review is to summarize the current understanding of the presence of immunoglobulins in human milk that are elicited by SARS-CoV-2 vaccines and to evaluate their ability to neutralize the virus. Additionally, we aim to quantify the side effects experienced by lactating mothers who have been vaccinated, as well as the potential for adverse effects in their infants. This study is critical because it can help inform decision-making by examining the current understanding of antibody secretion in breastmilk. This is particularly important because, although the virus tends to be less severe in younger individuals, infants who contract the disease are at a higher risk of requiring hospitalization compared to older children.