The forthcoming recommendation by the US Centers for Disease Control (CDC), telegraphed by US officials last week, is being driven by both the highly contagious new variant of the virus and early signs that protection from vaccines fades within months.

The move means that the biggest mass vaccination drive in US history, which has been only partially successful, will have to expand and continue.

The US is experiencing a fourth wave of the pandemic as the Delta variant spreads aggressively through unvaccinated communities in the US – notably southern states of Florida, Alabama, Mississippi, Louisiana and Texas – and causing an increasing number of “breakthrough infections” of fully inoculated people.

US has fully vaccinated 168 million people, or about 62 percent of the adult population as of August 16, according to the CDC. Those numbers are below benchmarks set by the Biden administration for the national vaccination programme by now.