Evaluation of Adverse Effects in Nursing Mothers and Their Infants After COVID-19 mRNA Vaccination

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. 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. 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. 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.