Intriguingly, PPARα and PPARγ have been proposed as effective adjuvants for the development of COVID-19 vaccines because these receptors through an increase in the population of regulatory T-cells via upregulation in FOXP3 mRNA expression (a transcriptional factor for the function and differentiation of regulatory T-cells) (1): stimulate memory T-cells (2), upregulate the γδ type of T-cells, and (3) prolong B-cell memory and improve the secondary antibody response and thus can induce long-term memory (176, 178). Here, PPARG is linked to COVID-19.