ABSTRACT
Four vaccines have been approved to date by the European Medicines Agency for the management of the COVID-19 pandemic in Europe, with all four licenced for administration from 5 years of age. One way to protect the vulnerable younger population such as newborns and infants is through passive immunity via breastfeeding. Many studies have revealed that human milk contains immunoglobulins (Ig) against the SARSCoV-2 virus, both after natural infection or vaccination. It is not known however, whether these antibodies can resist enzymatic degradation during digestion in the infant gastrointestinal (GI) tract or indeed protect the consumers. Here, we describe the validation of commercially available ELISA kits to detect IgA, secretory IgA (sIgA) and IgG antibodies in human milk and subsequently evaluated the vaccine-induced immunoglobulin profile of breastmilk from a cohort of lactating mothers vaccinated with either the Pfizer/BioNTech, Moderna or the Astra Zeneca vaccine. We also investigated the effect of a static in vitro digestion protocol representing the gastric and intestinal phases of infant digestion on the IgA and IgG concentrations. Our data show that there is an increase in Ig levels in human milk following vaccination and provide important information regarding the extent to which these antibodies can resist digestion in the infant GI tract.