A surge in coronavirus cases has hit at least 21 states, and hospitalizations also are rising in areas even with high vaccination rates.

As winter approaches, federal data shows that the daily case average in the US is now 78,500, a 23 percent increase over the past two and a half weeks, according to ABC News.

Several states including New York, New Jersey, Colorado, New Mexico and California have approved COVID-19 booster shots for anyone aged 18 or over in a bid to stop the surge.

At least 68.8 percent of people aged 12 and over are fully vaccinated against COVID-19. But the unvaccinated are still at a greater risk of contracting or dying from the virus, according to the US Centers for Disease Control and Prevention.

Vermont, a state where 72 percent of the population is vaccinated against COVID-19, reported 50 percent more coronavirus cases on average over the past two weeks. On Nov 11, there were 591 cases in Vermont, the highest case count on record.

In Essex County, the county with the lowest vaccination rate in Vermont, there were 1,022 cases per 100,000 people reported from Nov 2 to 8.

The US saw its first national increase in hospitalizations in 10 weeks, ABC News reported. There were at least 47,000 patients with COVID-19 in hospitals, an increase of 2,000 patients since Nov 8.

Hospitals in New Mexico, Colorado and Idaho said their intensive-care units were filling up with COVID-19 patients.

In Colorado, 94 percent of ICU beds were full as of Nov 12, and nonemergency surgeries were suspended to handle the crisis.

Dan Weaver, vice-president of communications at the University of Colorado Hospital, said in a statement: "We have been proactively postponing most non-urgent and nonemergent surgeries."

The hospital said that nearly 90 percent of coronavirus patients in their ICU were not vaccinated as of Nov 11.

Colorado state officials said on Monday that people attending public indoor events in Denver with more than 500 people must show proof of vaccination.

In New Mexico, the seven-day rolling average of COVID-19 cases is 1,000 per day, according to data from the state. It has risen 48 percent on average, over the past two weeks.

Mandate extended

Governor Michelle Lujan Grisham extended until Dec 10 a statewide mask mandate that requires masks to be worn inside public spaces, irrespective of a person's vaccination status, CNN reported.

New York City also reported a rise in coronavirus cases. The average of daily cases was 1,074 as of Sunday, 32 percent higher than it was two weeks ago, The New York Times reported.

According to the city's COVID-19 data web page, 80.3 percent of New York City adults are fully vaccinated.

New York Health Commissioner Dave Chokshi issued an advisory on Monday for all adults to receive a booster shot, as long as they had their last dose of the Moderna or Pfizer vaccine six months ago.

He urged healthcare providers not to turn anyone away who wants the booster.

Chokshi tweeted: "Booster doses can provide one more layer of reassurance, allowing us to breathe a bit easier, either for ourselves or our loved ones, particularly as we gather and travel around the holidays."

By Tuesday, 765,811 deaths had been reported in the US, data from Johns Hopkins University shows.