Secretion of COVID-19–Specific Immunoglobulin Antibodies in Breast Milk at 2 Weeks After Vaccination

Set of bottles with breast milk for baby and medical mask on yellow background. Maternity and baby care concept.
A prospective cohort trial assessed SARS-CoV-2-specific IgA and IgG antibodies in breastfeeding women who received both doses of the Pfizer-BioNTech vaccine.

At 6 weeks after vaccination against COVID-19, robust secretion of SARS-CoV-2-specific immunoglobulin A (IgA) and immunoglobulin G (IgG) antibodies were detected in the breast milk of women who received the Pfizer-BioNTech vaccine. These findings were reported in a letter published in JAMA.

Women (N=84) who were among the first vaccine-targeted groups (eg, healthcare workers) and were breastfeeding during the initial vaccine rollout in Israel were enrolled in a prospective cohort trial from December 23, 2020, to January 15, 2021. All participants received both doses of the Pfizer-BioNTech vaccine. Beginning 2 weeks after the first dose, the women provided breast milk samples weekly for 6 weeks. The samples were assessed for IgA and IgG antibodies.

A total of 504 breast milk samples were collected from women (mean age, 34 years) with infants aged a mean of 10.32 months. At the initial sampling 2 weeks after the first dose of the Pfizer-BioNTech vaccine, IgA antibodies had significantly increased (ratio, 2.05; P <.001), and 61.8% of the breast milk samples tested positive. At Week 4, 86.1% were positive for anti-SARS-CoV-2-specific IgA antibodies, increasing slightly through Week 6, at which time 65.7% of the samples tested positive.

For anti-SARS-CoV-2–specific IgG antibodies, few of the breast milk samples tested positive until Week 4 (mean, 20.5 U/mL; P =.004). At Week 5 and Week 6, 97% of the samples were found to be positive for IgG antibodies.

No serious adverse events were reported. The most commonly reported vaccine-related adverse event after the first (55.9%) and second (61.9%) doses was injection site pain. Fevers developed among 4 infants after maternal vaccination, 1 of whom was admitted for evaluation of fever and was treated with antibiotics.

This study was limited by the exclusion of functional assays or serum antibody testing.

The letter authors concluded that secretion of anti-SARS-CoV-2-specific IgA antibodies in breast milk could be detected as early as 2 weeks following vaccination and 4 weeks following vaccination for IgG antibodies. These findings suggested that there was the potential for a protective effect in breastfeeding infants of mothers who were vaccinated against COVID-19.


Perl SH, Uzan-Yulzari A, Klainer H, et al. SARS-CoV-2–specific antibodies in breast milk after covid-19 vaccination of breastfeeding women. JAMA. Published online April 12, 2021. doi:10.1001/jama.2021.5782