The US is “going in the wrong direction” on coronavirus as cases soar due to the Delta variant and a large proportion of unvaccinated people, the nation’s top infectious diseases expert has said.

Dr Anthony Fauci said the nation is “practically pleading” with people to get vaccinated as coronavirus cases surge once again in areas with low uptake.

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COVID-19 cases have nearly tripled in the US over the last two weeks, driven by the explosion of the Delta variant, especially in pockets of the South where vaccine hesitancy is high.

Louisiana, Arkansas, Missouri, Florida and Nevada – where vaccine rates are below the national average – are reporting the highest daily average of new cases per capita over the past week, all of which are at least double the overall US rate.

“This is an issue predominantly among the unvaccinated, which is the reason why we’re out there, practically pleading with the unvaccinated people to go out and get vaccinated,” Dr Fauci said.

“We’re going in the wrong direction”, he added, and described himself as “very frustrated” over the situation.

The US has seen an average of about 43,700 new cases per day over the past week – 65% over the previous seven days and nearly three times as high as the level two weeks ago, data compiled by Johns Hopkins University shows.

The Delta variant, first found in India and which has since been blamed for a rapid uptick in COVID cases in the UK, is causing 83% of new cases.

Dr Fauci, who also serves as President Joe Biden’s chief medical adviser, told CNN’s State of the Union that he has taken part in conversations about altering the guidelines on masks.

He said recommending that the vaccinated wear masks is “under active consideration” by the government’s leading public health officials as a way of turning the tide on infections.

He noted that some local jurisdictions where infection rates are surging, such as Los Angeles County, are already calling on individuals to wear masks in indoor public spaces regardless of vaccination status.

Back in April, America’s Centers for Disease Control and Prevention (CDC) updated its guidance to say that fully vaccinated people no longer had to wear masks in many settings.

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Booster jabs may also be suggested for people with suppressed immune systems, Dr Fauci said. The UK is already considering such a plan for those most vulnerable to COVID ahead of autumn and winter.

Dr Fauci said government experts are reviewing early data but that some of the most vulnerable, such as organ transplant and cancer patients, are “likely” to be recommended for booster shots.

More than 163 million people, or 49% of the total US population, are fully vaccinated, according to CDC data. Of those eligible for the vaccine, aged 12 and over, the figure rises to 57%.

However, rates are lower than the national average in some states, predominately Republican ones, where fewer than half of residents have received their first dose in some cases.

Florida, which has seen hospitalisations and cases jump 65% this week, has a vaccination rate of around 60%, on par with the national average. But some strongly conservative counties in the north of the state have a vaccination rate as low as 30%.

Republican lawmakers are under increasing pressure to persuade vaccine sceptics to roll up their sleeves and take the shots.

Dr Fauci praised some Republicans, including governors Asa Hutchinson of Arkansas and Ron DeSantis of Florida, and the second-ranking US House leader, Steve Scalise of Louisiana, for encouraging their constituents to get vaccinated but said more needed to speak out.

“What I would really like to see is more and more of the leaders in those areas that are not vaccinating to get out and speak out and encourage people to get vaccinated,” Dr Fauci said.