The new Omicron variant of COVID-19 has sparked a new wave of concern around the world since it emerged. Now, the World Health Organization (WHO) is sounding the alarm that it may be more contagious than previously known.

During a question and answer session on Friday over social media, Maria Van Kerkhove, the WHO’s COVID-19 technical lead, warned that the number of cases worldwide has been rising since the Omnicron variant first emerged. In the last two days, the strain has been detected in 38 countries up from 23, said Van Kerkhove, who cautioned that this variant may be more infectious than the previous Delta variant.

“There is a suggestion that there is increased transmissibility, what we need to understand is if it’s more or less transmissible compared to Delta,” Van Kerkhove said at the session.

The Delta variant has been the predominant strain throughout 2021 and Kerkhove said that the majority of cases that are being detected are Delta related. The two share some common symptoms, but Omicron patients have reported only mild symptoms but others, including younger patients, have reported more serious conditions like fatigue and body aches.

She made it clear that the data was still preliminary and acknowledged the mild symptoms that are associated with Omicron, but warned that it was too soon to dismiss it so early.

“Everybody who is infected with SARS-CoV-2 regardless of what variant will always start out with a mild disease," said Van Kerkhove. "And so maybe it will stop there with mild, some people are asymptomatic of course, but it may stop with mild disease or it may take some time.”

The Omicron variant was first designated as a new strain on Nov. 26 after emerging in southern Africa. Shortly after being reported on, several countries, including the United States, moved quickly to enact travel restrictions on travel from eight African countries and announced stricter screening requirements for travelers.