The 'Delta Plus' variant has spread to nearly 30 countries, but low case numbers are a sign it won't overtake Delta

• The Delta Plus variant, found in dozens of countries, is the Delta variant with an extra mutation.
• It's not yet clear whether Delta Plus is more transmissible than Delta.
• The fact Delta remains dominant worldwide, however, is a sign Delta Plus won't overtake it soon.

As the Delta coronavirus variant tears across the globe, scientists are keeping a close eye on its relative: Delta Plus.

The two variants are genetically similar, which is why they share the same Greek letter. But Delta Plus (also known as AY.1) has an extra mutation in the code for its spike protein, which helps the coronavirus access our cells.

India's health ministry said last month that Delta Plus appeared to spread more easily than Delta and might be able to bind more easily to lung cells or resist antibody drugs. But an Indian genomics consortium suggested more recently that Delta's sublineages probably weren't more transmissible than Delta. As of July 23, India had recorded no more than 70 Delta Plus cases.

The US Centers for Disease Control and Prevention and the World Health Organization track Delta Plus as part of the Delta variant, meaning the cases aren't separated. But data from Scripps Research's Outbreak.info tracker suggests just 430 Delta Plus cases have been detected worldwide.

South Korea on Tuesday announced it had recorded its first two cases of Delta Plus. The nation is recording its heaviest surge of infections yet, most likely driven by the original Delta strain.

"It doesn't terrify me any more, really, than Delta," Andrew Read, a Pennsylvania State University professor who studies the evolution of infectious diseases, said of Delta Plus.

Though Delta Plus has made its way to at least 29 countries and 17 US states, Read noted that "the widespread geographic nature doesn't mean that it's one thing spreading widely."

"It could be that it's several independent events that are spreading locally," he said.

In the US, Delta Plus cases peaked in late June at less than 5% of the nation's sequenced cases, according to Outbreak.info. Health experts say it's a sign Delta Plus isn't outcompeting other variants.

"If it started to rise in frequency against the Delta variant, that would tell you that it was perhaps on track to take over from Delta - but we're not really seeing that at the moment," Read said. "If it had a big advantage, we'd be seeing it rising in frequency pretty rapidly."

Scientists don't know how well vaccines perform against Delta Plus

For Delta Plus to be a serious concern, scientists would need evidence it's more transmissible than Delta, causes more severe disease, or resists protection from vaccines to a greater degree.

"I could imagine that, because the mutation is in the spike [protein], it might have some advantages in terms of immune evasion and some disadvantages in terms of binding to the ACE2 receptor," Read said. That receptor serves as the port of entry for the coronavirus.

But Public Health England told Insider in June that there was no evidence Delta Plus' extra mutation made the virus any more severe or reduced vaccine effectiveness relative to Delta.

While Delta seems to have challenged how well vaccines prevent infection and transmission, recent CDC data indicates coronavirus shots still reduce the risk of getting COVID-19 eightfold, and the risk of hospitalization or death twenty-fivefold.

A study in the New England Journal of Medicine found the two-dose Pfizer-BioNTech vaccine reduced the risk of a symptomatic Delta infection by 88%. Another study that hasn't been peer reviewed found the Pfizer-BioNTech and Moderna mRNA vaccines reduced the risk of hospitalization by 91% for people who weren't immunocompromised.

When it comes to Delta Plus, a study from Indian researchers that's still awaiting peer review found that Covaxin - one of India's two main coronavirus vaccines - still neutralized the variant. Covaxin is similar to China's Sinovac shot.