US Covid-19 cases are up around 11 per cent over the previous week, almost entirely among people who have not been vaccinated, officials said on Thursday, as the highly infectious Delta variant becomes the dominant Covid-19 strain in the country.

Around 93 per cent of Covid-19 cases in recent days have occurred in counties with vaccination rates of less than 40 per cent, US Centers for Disease Control and Prevention director Rochelle Walensky told a media briefing. Preliminary data from recent months suggest 99.5 per cent of Covid-19 deaths have occurred in unvaccinated people, she added.

“Simply put: In areas of low vaccination coverage, cases and hospitalisations are up,” Walensky said.

The CDC earlier this week said that the Delta variant of Covid-19 has become the dominant strain in the US. The variant, which is highly contagious, has also become dominant in other countries around the world.

Cases of Covid-19 are surging in counties representing 9 million people, Walensky said.

“Low vaccination rates in these counties coupled with high case rates and lax mitigation policies that do not protect those who are unvaccinated from disease will certainly and sadly lead to more unnecessary suffering,” she said.

Wall Street’s main indexes fell on Thursday as the spread of the Covid-19 Delta variant cast doubts over an economic recovery.

The White House is concentrating federal assistance for vaccinating against and treating Covid-19 in states including Arkansas, Missouri, Nevada and Illinois, said Jeff Zients, who leads the White House’s Covid-19 response team.

The White House last week said it would send out special teams to hot spots around the US to combat the Delta variant amid rising case counts. The White House is also working to make Covid-19 jabs available at doctors’ offices around the country, Zients added.