Infant Passive Protection Against Coronavirus Through Exclusive Breastfeeding: A Cross-Sectional Study.

Background/objectives: This study aimed to determine the percentage and duration of neutralizing antibodies against the Omicron variant in human milk after vaccination against SARS-CoV-2, considering the three different vaccine technologies approved in Brazil.

Methods: A cross-sectional study was conducted with lactating women who received the complete vaccination cycle with available vaccines (AstraZeneca, Pfizer, CoronaVac, and Janssen). The participants resided in Rio de Janeiro, and samples were collected from April to October 2022. Breast milk was analyzed for evidence of neutralizing antibodies using specific assays for the Omicron variant.

Results: The results showed that all types of vaccines were effective in inducing neutralizing antibodies in breast milk regardless of the vaccine technology used. There was no significant difference between women receiving two or three doses. Exclusive breastfeeding was significantly associated with higher percentages of neutralizing antibodies in breast milk compared to non-exclusive breastfeeding.

Conclusions: These findings reinforce the importance of breastfeeding as a strategy to provide passive protection to infants, especially where vaccination for children under six months of age is not recommended.