The country’s minister of health said on Sunday that two cases of the COVID-19 mutation had been discovered. Omicron has spread quickly and disrupted financial markets and world travel in the past five days. And U.S. health officials say it could already be in the U.S.

“We have not detected it yet, but when you have a virus that is showing this degree of transmissibility, and you’re already having travel-related cases—that they’ve been noted in Israel and Belgium and in other places—when you have a virus like this, it almost invariably is ultimately going to go essentially all over,” said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, on Saturday’s Weekend Today.

The Canadian cases involved two Ontario residents who were returning from Nigeria.

“Ottawa Public Health is conducting case and contact management, and the patients are in isolation,” officials said in a statement. “The Ontario COVID-19 Genomic Network is continuing to actively monitor for all potential variants circulating in the province, including the Omicron variant, and is conducting genomic sequencing on 100% of eligible COVID-19 positive samples.”

Omicron was first detected on Nov. 24, based on a specimen collected on Nov. 9. The World Health Organization has labeled it a “very high” global risk, saying that the “unprecedented number of spike mutations” in the variant could “impact the trajectory of the pandemic.”

Public health officials in South Africa say the symptoms so far seem mild, but health officials tell Fortune they are still waiting on hard data on severity. And there’s no data yet on how deadly Omicron may be among more vulnerable populations.

It will be mid-December or so before pharmaceutical companies have any information on how effective current vaccines are against the variant. BioNTech and Pfizer said that they can adapt their mRNA vaccine within six weeks and begin vaccine rollout within 100 days.