While some researchers argue it's still too soon to say, a growing number of epidemiologists, infectious disease researchers and public health experts think that the vaccination campaign may be helping the country win the race against the coronavirus, according to a report in NPR.org.

"I think we've hit a tipping point. We've really turned a corner on this latest wave. And I think that the worst days of the pandemic really are now behind us," Ashish Jha, the dean of the Brown University School of Public Health, was quoted as saying.

According to the US Centers for Disease Control and Prevention (CDC), an estimated 34 per cent proportion of the US population already have some immunity to the virus from having been exposed to the virus.

Added to this is the vaccination campaign, the report said. More than 43 per cent of the population has now gotten at least one shot, and a third are fully vaccinated. That's getting very close to where other countries, such as Israel, started to turn the corner and experience a precipitous drop in infections, it added.

The combination of natural immunity from people who were exposed and vaccination "means we may be closer to 60 per cent population immunity already," Jha said. "That's why I'm pretty confident we have turned the corner."

After months of rising, the number of daily infections in the US has begun to fall again. It has on average dropped 27 per cent in the last two weeks.

However, in places, such as Oregon, Washington state, and parts of Colorado and Arizona, the infections are spreading fast, leading experts to warn  people of letting down their guard too soon.

"There was a fourth surge, whether it's already receding isn't yet knowable. It didn't feel so bad because it was so much smaller than the third. It has been a bit larger than the second, and may not be over yet," Thomas Frieden, a former director of the CDC, was quoted as saying.