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A so-called Delta Plus variant of SARS-CoV-2 is back in the news after a former senior U.S. health official noted its increasing prevalence in the U.K. and called for “urgent research.”

Scott Gottlieb, who was commissioner of the Food and Drug Administration for two years under former President Donald Trump, tweeted Sunday that researchers need to figure out if Delta Plus is more transmissible and whether it can evade COVID-19 immunity to any degree.

He subsequently pointed out that there was no “cause for immediate concern” and that Delta Plus’s rise was “a reminder that we need robust systems to identify [and] characterize new variants.” With that cautious reassurance in mind, here’s what you need to know about the variant in question.

Why is it called Delta Plus?

There are actually several flavors of Delta Plus, with the one Gottlieb highlighted being known as AY.4. All are sub-variants of Delta, which was first spotted in India, and which went on to become the predominant strain of the coronavirus around the world several months ago. One of the Delta Plus mutations, known as K417N, lies in its spike protein—the same mutation is also found in the Beta variant, which was first identified in South Africa.

Delta Plus was first identified in the U.K., though it is thought to have originated in India. Indian authorities have labeled it a “variant of concern”—the term that the World Health Organization (WHO) and others use for particularly troubling variants such as Delta and Beta. The Indian health ministry said this was because it was particularly transmissible and potentially resistant to treatment with monoclonal antibodies.

However, outside observers said it was too soon to draw such conclusions, and India still remains an outlier in classifying Delta Plus in this way.

What do we know about it now?

A study led by Germany’s Leibniz Institute for Primate Research showed earlier this month that Delta Plus was, like Delta itself, more efficient than other variants at invading lung cells, and at resisting treatment. Delta Plus particularly seems to resist the monoclonal antibodies bamlanivimab and etesevimab, which can prevent hospitalization in some cases of COVID-19 infection.

However, unit head Stefan Pöhlmann said vaccines offered comparable protection against both strains, meaning “Delta Plus is not significantly more dangerous than Delta.”

That study found that a combination of the Oxford/AstraZeneca and Pfizer/BioNTech vaccines “might provide particularly robust protection” against both Delta and Delta Plus. A separate study found that India’s Covaxin vaccine is effective against Delta Plus, much as it is against Delta.

Is Delta Plus spreading?

That depends where you look. Gottlieb said in his tweet that the AY.4 version of Delta Plus is spreading in the U.K. and now accounts for 8% of all genome-sequenced cases there. It is also on the rise in India. However, the global picture does not yet suggest Delta Plus is taking off across most of the world. This suggests it cannot outcompete Delta itself.

Gottlieb associated the rise of Delta Plus with the U.K.’s biggest one-day case increase in three months. Indeed, British infection rates are again near the peak from last winter’s second wave, with over 40,000 cases being identified each day.

However, there are many potential reasons for this, with one factor likely being the reluctance of British teenagers to get vaccinated, despite their return to school. According to recent figures, only 15 local authorities in England have managed to give a first shot to a quarter of 12- to 15-year-olds, and acceptance is below 10% in around a third of the country.