The Delta variant of the coronavirus has become the dominant strain in the U.S., and experts are warning that its continued spread poses a major risk to those who are unvaccinated.

“So far, almost all of the hospitalizations and deaths that we’re seeing — upwards of 99% of those cases — are among the unvaccinated,” Kristen Choi, assistant professor at UCLA School of Nursing, said on Yahoo Finance Live (video above). “So despite this variant — the way it’s changed, that’s it’s more transmissible — vaccines are still our No. 1 line of defense. And it’s going to be critical that we keep making progress on getting adults and kids vaccinated here in the U.S.”

The vaccination rate in the U.S. has slowed significantly. Currently, 57.1% of individuals over the age of 12 are fully vaccinated and 65.8% have received at least one dose. But since the beginning of July, the numbers have started to dip.

The reasons why unvaccinated individuals have avoided the vaccine range from political beliefs to skepticism about the scientific data.

“When it comes to the unvaccinated, in my own research I’ve done on people who have refused the coronavirus vaccine, it’s often not so much a case that people haven’t seen the data or aren’t aware of the data,” Choi said. “It’s much more a question of people’s personal fears and personal beliefs that tend to get in the way more so than a lack of data.”

Delta variant is '2020 version of COVID-19 on steroids'

The Delta variant, or mutant strain of coronavirus, accounts for roughly 83% of new COVID cases in the U.S., according to CDC Director Rochelle Walensky.

The strain is ravaging India, where there have been over 31 million cases and more than 418,000 deaths. Now, the U.K. is seeing an influx in cases driven by the variant as well, with a 74% jump in cases over the past 14 days. India’s fully vaccinated rate is just 6.3% while the U.K.’s is 54%.

The key thing that sets the Delta variant apart from other strains is that it's significantly more contagious.

Andy Slavitt, former senior adviser to the White House's COVID Response Team, described the variant as “the 2020 version of COVID-19 on steroids.”

But scientific data has indicated that the three main vaccines in the U.S. — from Pfizer (PFE), Moderna (MRNA), and Johnson & Johnson (JNJ) — are all effective against it, though slightly weaker.

“The good news is that we do have some pretty good protection against the Delta variant from our vaccines,” Choi said. “So far they’ve all held up very well against the variants. They’re a bit less effective against the variant than the original coronavirus strain. But nevertheless, they appear to be very effective at preventing hospitalizations and deaths.”