CD40LG and COVID-19: We identified 10 published studies on the immune response to an mRNA-based COVID-19 vaccine in breast milk of lactating women.9–18 The number of lactating women included in eight of these studies ranged between five and 31; two remaining studies included 84 and 110 lactating women.17,18 All studies measured levels of SARS-CoV-2–specific IgA and IgG and, in some cases, SARS-CoV-2–specific IgM.