The breastfeeding women belonging to risk groups were encouraged to receive the vaccine under Israel national vaccination program against COVID-19, despite their exclusion in vaccine trials and without any published vaccine-related safety data in this population. The Centers for Disease Control and Prevention also recommends breastfeeding women belonging to vaccine-target groups be immunized. 

A study investigated the secretion of SARS-CoV-2 antibodies into breast milk after maternal immunization and also evaluated any potential adverse events among women and their infants.

A convenience sample of breastfeeding women (either exclusive or partial) belonging to vaccine-target groups who chose to be vaccinated (receiving 2 doses of the Pfizer-BioNTech vaccine 21 days apart) was examined. Breast milk samples were collected before administration of the vaccine, followed by once a week for 6 weeks starting at week 2 following the first dose. 

IgG levels were detected and read, with a level of more than 0.8 U/mL considered positive and IgA with an extinction ratio of samples over calibrator of more than 0.8 considered positive.

Maternal and infant demographic information was collected at baseline, followed by weekly questionnaires related to breast milk collection interviewing information about interim well-being and vaccine-related adverse events. 

Changes in the proportion of participants with positive test results and antibody levels during the study were evaluated.

The following observations were made-

• 4 women completed the study, providing 504 breast milk samples.
• The mean (SD) age of women was 34 (4) years and infants were 10.32 (7.3) months.
• Mean levels of anti–SARS-CoV-2-specific IgA antibodies in the breast milk showed a rapid increase and were markedly elevated at 2 weeks after the first vaccine, when 61.8% of samples tested positive, rising to 86.1% at week 4 (1 week after the second vaccine).
• Mean levels remained elevated for the duration of follow-up, and 65.7% of samples tested positive at week 6.
• Anti–SARS-CoV-2-specific IgG antibodies were low in the first 3 weeks, which increased at week 4, when 91.7% of samples tested positive, which further increased to 97% at weeks 5 and 6.
• No mother or infant encountered any serious adverse event during the study period.
• 55.9% of women reported a vaccine-related adverse event after the first vaccine dose and 61.9% after the second vaccine dose, with local pain being the commonest complaint.
• Four infants developed a fever during the study period at 7, 12, 15, and 20 days after maternal vaccination.
• Symptoms of upper respiratory tract infection including cough and congestion were reported in all the infants which resolved without treatment except for 1 who was admitted and treated with antibiotics. 

Thus a robust secretion of SARS-CoV-2 specific IgA and IgG antibodies were demonstrated in breast milk for 6 weeks after vaccination. IgA secretion was apparent at about 2 weeks after vaccination followed by a spike in IgG after 4 weeks. Antibodies found in the breast milk of these women demonstrated strong neutralizing effects, indicating a probable protective effect against infection in the infant.

Source- 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. 2021;325(19):2013–2014. doi:10.1001/jama.2021.5782