PRL and COVID-19: Even though the reasons for increased frequencies of RBD-reactive memory B cells are likely multifactorial, increased levels of milk-inducing prolactin have been associated with increased antibody titers and activated “memory”-like B and T cells.61, 62, 63, 64, 65, 66 As memory B cells have been proposed to play a key role in mounting recall responses to COVID-19 mRNA vaccines,38 further studies will be needed to determine if these cellular differences are maintained in the medium term and whether they will affect long-term protection.