SARS-CoV-2 variants:A continuing threat to global health

Coronavirus disease 2019(COVID-19)is an acute respiratory illness caused by severe acute respiratory syndrome coronavirus 2(SARS-CoV-2).COVID-19 pandemic has an unprecedented impact on economy,trade and human lifestyle globally.Since the emergence of of SARS-CoV-2,more than 266 million infections and 5260888 deaths were reported globally over the last two years[1].The scientific achievements particularly in last two years yielded effective vaccines against COVID-19.A variety of platform technologies including protein subunit,viral vector,RNA,inactivated and DNA are being employed to develop effective vaccines.To date,vaccines that have been approved against COVID-19 include the Pfizer BioNTech(mRNA vaccine),Oxford-AstraZeneca(viral vector vaccine),Moderna(mRNA vaccine),Janssen Ad26.COV2.S(viral vector),Sinopharm,Sinovac-CoronaVac,Bharat Biotech’s Covaxin(inactivated virus vaccines),etc.As of December 2021,over 8 billion doses of COVID-19 vaccines have been administered globally[1].The details on the number of COVID-19 confirmed cases and global vaccination coverage are provided in Figure 1.