South African scientists identified a new version of the coronavirus that they say is behind a recent spike in Covid-19 infections in Gauteng, the country’s most populous province.

It’s unclear where the new variant first emerged, but scientists in South Africa alerted the WHO in recent days. On Friday, the WHO designated it as a “variant of concern”, naming it “Omicron” after a letter in the Greek alphabet.

What do we know about Omicron?

Health minister Joe Phaahla said the variant was linked to an “exponential rise” of cases in the last few days. From just over 200 new confirmed cases per day in recent weeks, South Africa saw the number of new daily cases rocket to more than 3,200 on Saturday, most in Gauteng..

Why are scientists worried about it?

After convening a group of experts to assess the data, the WHO said that “preliminary evidence suggests an increased risk of reinfection with this variant”, as compared to other variants.

That means people who contracted Covid-19 and recovered could be subject to catching it again. The variant appears to have a high number of mutations — about 30 — in the coronavirus’ spike protein, which could affect how easily it spreads to people.

Sharon Peacock, who has led genetic sequencing of Covid-19 in Britain at the University of Cambridge, said the data so far suggest the new variant has mutations “consistent with enhanced transmissibility”.

What’s known and not known about virus?

Scientists know that Omicron is genetically distinct from previous variants including the beta and delta variants, but do not know if these genetic changes make it any more transmissible or dangerous. So far, there is no indication the variant causes more severe disease.

It will likely take weeks to sort out if Omicron is more infectious and if vaccines are still effective against it.

How did this variant arise?

The coronavirus mutates as it spreads and many new variants, including those with worrying genetic changes, often just die out. Scientists monitor Covid-19 sequences for mutations that could make the disease more transmissible or deadly, but they cannot determine that simply by looking at the virus. Peacock said the variant “may have evolved in someone who was infected but could then not clear the virus”.