Assessment of SARS-CoV-2 neutralizing from convalescent and vaccinated mothers

Breastmilk contains antibodies that could protect breastfed infants from infec-tions. In this work, we examined if antibodies in breastmilk could neutralize SARS-CoV-2 in 84 breastmilk samples from women that were either vaccinated (Comirnaty, mRNA-1273, or ChAdOx1), infected with SARS-CoV-2, or both in-fected and vaccinated. The neutralization capacity of these sera was tested using pseudotyped vesicular stomatitis virus carrying either the Wuhan-Hu-1, Delta, or BA.1 Omicron spike proteins. We found that natural infection resulted in higher neutralizing titers and that neutralization correlated positively with levels of immunoglobulin A in breastmilk. In addition, significant differences in the capac-ity to produce neutralizing antibodies were observed between both mRNA-based vaccines and the adenovirus-vectored ChAdOx1 COVID-19 vaccine. Over-all, our results indicate that breastmilk from naturally infected women or those vaccinated with mRNA-based vaccines contains SARS-CoV-2 neutralizing anti-bodies that could potentially provide protection to breastfed infants from infec-tion.