(NEXSTAR) — The latest surge in COVID-19 infections is fueled by the highly contagious delta variant first identified in India late last year. Now, a variation of that variant is beginning to generate headlines. Here’s what we know about the COVID sub-strain being called delta plus.

The delta plus variant is similar to the existing delta variant except that it has a spike protein mutation called the K417N. Spike proteins are external bumps the virus uses to hook onto human cells. The delta plus mutation is the same one previously identified on the beta variant. According to the Washington Post, some experts believe delta plus could be even more contagious than the now dominant delta variant, but there is no widespread consensus on that conclusion at this point.

To date, relatively few delta plus cases have been sequenced, but it has been detected in the United States, as well as the United Kingdom and India, according to the Washington Post. On Tuesday, South Korea announced it had identified its first two cases of delta plus, according to Reuters. One of those cases is reportedly a traveler returning from the United States.

American researchers told the Post that it’s still too early to determine whether this delta plus variant could prove more vaccine-resistant or contagious than the existing delta variant.

Centers for Disease Control Director Dr. Rochelle Walensky recently confirmed just how much more contagious delta is compared to the original strain that caused the first wave of global infections.

“If you get sick with the alpha variant, you could infect about two other unvaccinated people,” she said. “If you get sick with the delta variant, we estimate that you could infect about five other unvaccinated people — more than twice as many as the original strain.”

Last week, the CDC reversed course on masks, recommending that even vaccinated people again mask up indoors in areas where the virus is on the march, now most of the country.

The immediate reason was a report by disease detectives of a recent outbreak in Provincetown, Mass. The delta variant was to blame and a majority of those infected had been vaccinated. Although very few vaccinated people got sick enough to be hospitalized, the initial findings showed vaccinated people with breakthrough infections were carrying about as much virus as unvaccinated people.

In all, there were more than 4 million new COVID-19 cases reported globally in the last week, driven mostly by spikes in the Middle East and Asia.

The Associated Press contributed to this report.