BackgroundRecent studies have shown the presence of SARS-CoV-2-specific antibodies in the milk of breastfeeding mothers vaccinated with mRNA and convalescent. However, limited information is available in lactating women receiving other vaccine platforms used in developing countries, such as the inactivated SARS-CoV-2 vaccine BBIBP-CorV (Sinopharm) and the non-replicating adenovirus vaccines Sputnik V (Gamaleya Institute) and ChAdOx1-S (Oxford AstraZeneca).MethodsHere, we evaluated anti-SARS-CoV-2 IgG and IgA levels in both serum and milk samples using a longitudinal and a cross-sectional cohort of 208 breastfeeding vaccinated women from Argentina with or without previous SARS-CoV-2 infection.ResultsThe analysis showed that IgA levels remain constant in serum and milk of breastfeeding mothers between the first and second doses of vector-based vaccines (Sputnik V and ChAdOx1-S). After the second dose, anti-spike IgA was found positive in 100% of the serum samples and in 66% of breastmilk samples. In addition, no significant differences in milk IgA levels were observed in participants receiving BBIBP-CorV, Sputnik V or ChAdOx1-S. IgG levels in milk increased after the second dose of vector-based vaccines. Paired longitudinal samples taken at 45 and 120 days after the second dose showed a decrease in milk IgG levels over time. Study of IgA levels in serum and milk of vaccinated naïve of infection and vaccinated-convalescent breastfeeding participants showed significantly higher levels in vaccinated-convalescent than in participants without previous infection.ConclusionThis study is relevant to understand the protection against SARS-CoV-2 by passive immunity in newborns and children who are not yet eligible to receive vaccination.

Sasan Haghani, Ph.D., is an Associate Professor of Electrical and Computer Engineering at the University of the District of Columbia. His research interests include the application of wireless sensor networks in biomedical and environmental domains and performance analysis of communication systems over fading channels.Daniel Albano, Northrop Grumman Corp.Daniel Albano is a graduate of the University of the District of Columbia's Electrical Engineering Masters program. He currently works as a Digital Electronics Engineer at Northrop Grumman Corporation. Dr. Wagdy H. Mahmoud, University of the District of ColumbiaWagdy H. Mahmoud is an Associate Professor of electrical engineering at the Electrical Engineering Department at UDC. Mahmoud is actively involved in research in the areas of reconfigurable logic, hardware/software co-design of a system on a chip using reconfigurable logic, application-specific integrated circuits (ASIC), digital logic design, image compressions, digital signal processing, computer architecture, embedded systems, system on a chip, and renewable energy.