“…Unfortunately, the immunity conferred by natural infection and the different vaccines is not sterilizing, or the level of protective immunity diminishes after some time. For that reason, infections or reinfections have been observed in both cases [ 129 , 130 ], although with less severe symptoms [ 131 , 132 , 133 , 134 , 135 ]. New virus varieties keep spreading among the populations, seriously affecting the unvaccinated or those with comorbidities [ 129 , 130 , 131 , 132 , 133 , 134 , 135 ], which is an indication that herd immunity has not been achieved in the different countries, regions, or population sectors [ 42 , 135 , 136 , 137 , 138 , 139 , 140 , 141 , 142 ].…”