Breastfeeding rendered crucial for preterm infants during COVID-19 pandemic. However, the role of donated human milk (DHM) in the protection against SARS-CoV-2 infection when own mother’s milk is not available or insufficient remains unclear. Pasteurization of DHM contributes to the loss of some biological and nutritional properties of human milk. The presence of specific breast milk SARS-CoV-2 antibodies has been demonstrated in women after COVID-19 disease and after vaccination. We aimed to evaluate the impact of Holder pasteurization on vaccinated donor women’s milk and to identify the impact on the concentrations of specific immunoglobulins (Ig) against SARS-CoV-2. A prospective, observational, exploratory pilot study in lactating women (n=12) who received the complete course of mRNA-based vaccines (BioNTech/Pfizer) against SARS-CoV-2 infection was conducted. Levels of antibodies directed to structural receptor-binding domain of the SARS-CoV-2 spike protein were determined by ELISA before and after pasteurization. IgA and IgG anti-SARS-CoV-2 immunoglobulin concentrations were significantly reduced after Holder pasteurization. Interestingly, there was a negative correlation between the initial amount of anti-SARS-CoV-2 antibodies and the percentage of their recovery after the pasteurization for both isotypes. Despite the partial loss of immunoglobulins still a high percentage of antibodies remained after the pasteurization, a mean of 70.53 (3.4)% of anti-SARS-CoV-2 IgA and 81.99 (21.89)% of IgG antibodies. Our study underscores the potential relevance of breast feeding or alternatively DHM to provide babies at risk with virus-specific SARS-CoV-2 antibodies thus protecting them against COVID-19.

We thank the support and guidance of M.C. Collado and C. Martinez-Costa. We thank all the families who were involved in the study during this difficult time and in the middle of the COVID-19 pandemic as well as the collaborators of the MilkCORONA study team and, the support received by the research grant from LaMarató-TV3 (ref. 31/109/202106).

No