COVID-19(13) age(11) SARS-CoV-2(10) Patient(7) Infection(7) Older(7) severity(6) immunosenescence(6) Health(5) Result(5) pandemic(5) outcome(5) vaccination(4) COVID-19 pandemic(4) SARS-CoV-2 vaccine(4) mechanism(4) frailty(4) risk(4) diabetes(4) disease(4) syndrome(4) Mild(4) elderly(4) reported(4) hypertension(3) immune system(3) Hospitalization(3) risk factor(3) moderate(3) Host(3)