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 World Health Organization in recent days, and it has now been seen in travelers arriving in several countries, from Australia to Israel to the Netherlands. 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 Saturday, most in Gauteng. Struggling to explain the sudden rise in cases, scientists studied virus samples and discovered the new variant. Now, as many as 90% of the new cases in Gauteng are caused by it, according to  Tulio de Oliveira, director of the KwaZulu-Natal Research Innovation and Sequencing Platform. WHY ARE SCIENTISTS WORRIED ABOUT THIS NEW VARIANT? 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," but said that "the significance of many of the mutations is still not known." Lawrence Young, a virologist at the University of Warwick, described omicron as "the most heavily mutated version of the virus we have seen," including potentially worrying changes never before seen all in the same virus. READ: What is this new COVID variant in South Africa? WHAT'S KNOWN AND NOT KNOWN ABOUT THE VARIANT? 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. Peter Openshaw, a professor of experimental medicine at Imperial College London said it was "extremely unlikely" that current vaccines wouldn't work, noting they are effective against numerous other variants.