It has been over a year and a half since the coronavirus disease 2019 (COVID-19) pandemic began to besiege the world, forcing a large-scale shut-down of business activity, travel, educational and sports institutions, and placing an overwhelming burden on healthcare systems in many countries worldwide. Meanwhile, survivors and vaccine recipients wonder: how long will they remain immune against re-infection, and will they still be vulnerable to the newer variants of concern (VOCs) of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)?
