CD4 and AIDS: The observed increase in humoral response in our setting is also consistent with the hypothesis that third dose induces a robust B cell memory response29, previously elicited by the primary vaccination series and highlights the fact that the SARS-CoV-2 mRNA vaccines are able to stimulate a satisfactory humoral response even in immunocompromised patients such as those with low CD4 count and a previous or current diagnosis of AIDS.