“…This is important because otherwise, known age-related changes in the immune system would confound the results of each study. The published study designs varied from observational [ 74 , 80 , 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 ] to interventional studies and clinical trials [ 83 , 85 , 86 , 101 , 102 ]. Furthermore, humoral responses were reported according to seroconversion, antibody concentration/titers, and, in some cases, virus neutralization/pseudo-neutralization capacity ( Figure 3 and Table 1 ).…”