CD4 and infection: The same response that occurs with natural infection could be expected with vaccines, such as those developed by Pfizer-BioNTech, Moderna and Oxford-Astrazeneca, since they stimulate the humoral immune response directed to the SARS-CoV-2 spike protein (144–146) At the same time, it has also been seen that although the memory immune response remains for several months, it decreases over time; such is the case of the neutralizing antibody response and spike-specific CD4 + T cells, which diminish in the former 4 months post-infection.