WASHINGTON - US health authorities on Friday pleaded with Covid vaccine holdouts to roll up their sleeves and get their shots, as cases, hospitalizations and deaths surged.

"There is a clear message that is coming through: this is becoming a pandemic of the unvaccinated," Centers for Disease Control and Prevention director Rochelle Walensky told reporters.

The agency reported more than 33,000 new cases on Thursday, bringing the seven-day average up to 26,306, a 70 percent rise on the week before.

The seven-day average of hospital admissions is about 2,790 per day, an increase of 36 percent. And after weeks of declines, the seven-day average of deaths was 211, an increase of 26 percent.

The spikes are focused in communities with low vaccination rates, and "unvaccinated Americans account for virtually all recent COVID-19 hospitalizations and deaths" said Jeff Zients, White House coronavirus response coordinator.

The new wave is driven by the Delta variant, which now accounts for more than 80 percent of new cases, according to the covSpectrum tracker.

A recent study in the journal Virological shows Delta grows more rapidly inside the body compared to past strains, and people who are infected shed much more of it in the air, greatly increasing the likelihood it will be transmitted.

Vaccines, including those made by Pfizer, Moderna, and Johnson & Johnson, remain highly effective against the variant, but the United States' immunization campaign has drastically slowed in recent weeks.

President Joe Biden set July 4 as a target for 70 percent of adults to have received one or more doses, but as of July 15 the figure was still only 67.9 percent. At the present rate the goal won't be achieved until the end of the month.

Parts of the country that voted for former Republican president Donald Trump in the 2020 election have significantly lower vaccination rates than those which voted for Democrat Biden, and are now at the center of the surges.

Hotspots include Missouri, Arkansas, and Louisiana.

But health officials are hopeful that, since 80 percent of the most vulnerable age group of over-65s are fully vaccinated, the rise in hospitalizations and deaths won't be as dramatic as the spike in cases.

This would follow the pattern seen in Israel and Britain, highly vaccinated countries struck by Delta waves.

An expert panel convened by the CDC will next week be examining whether immune-compromised people, whose bodies mounted a subpar response to Covid vaccines, may require a third dose, said Walensky.

AFP