Study strengths and limitations
To our knowledge, this is the largest series of breast milk samples from women with SARS-CoV-2 infection during pregnancy or at the time of delivery. We also collected paired colostrum and mature milk samples from many women and, for many of them, their serological status at the time of milk sampling was also recorded, which allowed us to study correlations between colostrum, mature milk and maternal serological status. Additionally, the protocol for collection, handling and storage of samples9 was early defined and implemented in all centers.
However, the main limitations relate to the small sample size and the additional technical difficulties that reduced the sample further, which may have prevented us to recognize any other association or significant finding.