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

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.

SARS-CoV-2 Antibodies in Breast Milk After Vaccination.

BACKGROUND AND OBJECTIVES: Passive and active immunity transfer through human milk (HM) constitutes a key element in the infant's developing immunity. Certain infectious diseases and vaccines have been described to induce changes in the immune components of HM. METHODS: We conducted a prospective cohort single-institution study from February 2 to April 4, 2021. Women who reported to be breastfeeding at the time of their coronavirus disease 2019 (COVID-19) vaccination were invited to participate. Blood and milk samples were collected on day 14 after their second dose of the vaccine. Immunoglobulin G (IgG) antibodies against nucleocapsid protein as well as IgG, immunoglobulin M and immunoglobulin A (IgA) antibodies against the spike 1 protein receptor-binding domain against severe acute respiratory syndrome coronavirus 2 (anti-SARS-CoV-2 RBD-S1) were analyzed in both serum and HM samples. RESULTS: Most of the participants (ie, 94%) received the BNT162b2 messenger RNA COVID-19 vaccine. The mean serum concentration of anti-SARS-CoV-2 RBD-S-IgG antibodies in vaccinated individuals was 3379.6 ± 1639.5 binding antibody units per mL. All vaccinated study participants had anti-SARS-CoV-2 RBD-S1-IgG, and 89% of them had anti-SARS-CoV-2 RBD-S-IgA in their milk. The antibody concentrations in the milk of mothers who were breastfeeding 24 months were significantly higher than in mothers with breastfeeding periods <24 months (P < .001). CONCLUSIONS: We found a clear association between COVID-19 vaccination and specific immunoglobulin concentrations in HM. This effect was more pronounced when lactation periods exceeded 23 months. The influence of the lactation period on immunoglobulins was specific and independent of other variables.