Joe Biden on Tuesday urged more Americans to get vaccinated against Covid-19 as cases begin to rise again across the US, fuelled largely by the Delta variant.

The US president announced a series of measures to encourage vaccinations, as officials said the virus was likely to spread in parts of the country with low inoculation rates.

Biden’s warning came as the highly transmissible Delta variant sweeps through the UK, which has a similar vaccination rate to the US, causing a surge in cases.

The UK death rate remains low, but US officials have warned in recent days about pockets of the country where low vaccination rates make people particularly at risk from a new wave of infections.

“Millions of Americans are still unvaccinated and unprotected. And because of that, their communities are at risk, their friends are at risk, the people they care about are at risk,” Biden said on Tuesday. “This is an even bigger concern because of the Delta variant.”

The US is recording an average of about 13,000 new cases a day, up from just over 11,000 two weeks ago. Health officials worry that regions with low vaccination rates will become hotspots that could drive a surge in hospitalisations and allow the virus to mutate further as it circulates.

In Missouri, the Delta strain makes up about 90 per cent of new coronavirus infections, according to a Financial Times analysis, and rising cases have forced some hospitals to move patients to other facilities. One hospital said it faced a temporary ventilator shortage over the Independence Day weekend.

About 39 per cent of the population in Missouri is fully vaccinated.

Rochelle Walensky, head of the US Centers for Disease Control and Prevention, said last week that there were 1,000 counties across the country where vaccination rates remained below 30 per cent.

The CDC has calculated that the Delta variant accounts for about a quarter of all US infections.

Meanwhile, data from Israel over the weekend suggested the BioNTech/Pfizer vaccine, which accounts for more than half of the doses administered in the US, is 64 per cent effective at preventing infection from the Delta variant — lower than it was for previous strains.

The measures announced by Biden on Tuesday included setting up vaccination clinics in workplaces, establishing more mobile vaccination clinics and improving access for adolescents aged 12-18.

The administration will also supply more doses to doctors’ offices and send advocates to visit people on their doorstep to provide information about the vaccines.

Additional reporting by James Politi in Washington