Effectiveness of COVID-19 vaccination in breastfeeding women in preventing SARS-CoV-2 infection in infants

Objective: To compare the COVID-19 transmission rates between infants who were primarily breastfed and those formula fed in mothers who received at least 2 doses of the COVID-19 vaccines. Methods: A prospective longitudinal study was conducted during the Omicron wave (January 1-October 1, 2022). Infants who exhibited respiratory symptoms were tested for SARS-CoV-2 by RT-PCR. Results: Of 234 infants, 66 (28.2%) tested positive for SARS-CoV-2, with 63 out of the 66 (95.5%) having a mother with COVID-19, and a median (IQR) age at diagnosis of 11.3 (10.8-11.9) months. The proportions of COVID-19 in 6- and 12-month breastfed and formula fed dominant infants were 27.0% vs. 31.0%, p =0.53 and 21.1% vs. 31.3%, p =0.11, respectively. In the multivariate Cox regression models, both 6- and 12-month breastfed only/dominant infants had a protected effect against COVID-19 with hazard ratios (HRs, 95% CI) of 1.50 (0.90, 2.51), p =0.13 and 1.63 (0.90, 2.51), p =0.09, respectively. Maternal vaccine regimens had no protective effect against COVID-19 with the HR of 0.86 (0.49, 1.52), p =0.61. In sub-group analysis, infants with a mother that had received 2 doses within 6 months and were breastfed only/dominant at 12 months had a protected effect against COVID-19 with the HR of 3.77 (0.77, 18.43), p =0.05. Conclusion : Mothers who have experienced COVID-19 can nurse without increasing the risk of SARS-CoV-2 transmission. Despite the possibility that breastfeeding mothers who receive the COVID-19 vaccine can shield their infants from the virus, the statistical evidence is insignificant.