CD40LG and COVID-19: The vaccinated and control groups will be compared according to COVID-19 related outcomes.<h4>Main outcomes</h4>The primary outcomes are the incidence coefficient of infection by SARS-CoV-2 determined by RT-PCR of naso-oropharyngeal swab specimen or rapid lateral flow IgG and IgM test, and presence of general COVID-19 symptoms, disease severity and admission to hospital during the 180 days of follow up.