COVID-19 vaccines and coronavirus 19 variants including alpha, delta, and omicron: present status and future directions

Coronavirus disease 2019 (COVID-19) is caused by a coronavirus, also called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). It has caused urgent global health problems worldwide. The rapid spread of this pathogen, the development of its variants, and the escalating number of patients and their deaths prompted scientists to take up the race for immediate development of COVID-19 vaccines. With regard to the technologies available for vaccine development, mRNA-, inactivated virus-, viral vector-, and protein subunit-based vaccines have been developed thus far. This review article aimed to epitomize the current intelligence and improvements of various vaccines against COVID-19, explicitly those approved for urgent use.