Background and Objectives: Breastfeeding women are generally excluded from clinical trials with new vaccines. The objective of the study was to explore whether the BNT162b2 mRNA and mRNA-1273 COVID-19 vaccines are safe for breastfeeding mothers and their breastfed infants. Methods: A convenience sample prospective cohort single institution study was performed on breastfeeding health care professionals, who were exposed to second dose of SARS-CoV2 vaccine at the beginning of the study period. They and their breastfed children's symptoms were followed up through online questionnaires for 14 days. Results: Of the 95 finally included participants, only 1 was lost to follow-up on day 7. Mean age of the mothers was 35.9 ± 3.9 years and that of their infants was 14.6 ± 12.1 months. At least one adverse event was reported by 85% (95% confidence interval [CI]: 76-91.5%) of the mothers. The most frequent was injection site pain in 81% of cases. Moreover, 31% (95% CI: 22-41%) observed some event in their breastfed children. Most frequently, 19% (95% CI: 13-30%) of the children were irritable. During the 14 days of follow-up, 36% of the children (95% CI: 27-46%) were diagnosed with respiratory infection. Conclusions: Most mothers' reactions were mild and transitory, generally limited to the first 3 days after vaccination. Many children's events were associated with concomitant infectious processes and we did not detect a notable peak on any particular day of follow-up. Neither mothers nor their infants developed serious adverse events nor were they diagnosed with COVID-19 within the study period.
Keywords: COVID-19; breastfeeding; human milk; reactogenicity; vaccine.