Dr. Leong Hoe Nam, speaking to CNBC, said he expects the virus will have spread to “practically everybody” by the time vaccines are ready for it, given their three- to six-month testing period.

“Frankly, Omicron will dominate and overwhelm the whole world in three to six months,” he said.

Overwhelm doesn’t mean decimate, though. Health officials are still assessing the seriousness of the mutation, including exactly how contagious it is. Vaccines seem to be effective against severe cases of Omicron, GlaxoSmithKline and the World Health Organization found.

And scientists and health experts say they have yet to see severely ill patients, noting there is no evidence the Omicron variant is more deadly than previous strains.

“The early information about severity of illness is reassuring; we’re not hearing anything that really alarms us,” Catherine Bennett, chair of epidemiology at Deakin University in Australia, told Fortune.

The first case of Omicron in the U.S. was announced Wednesday, followed by more reports Thursday. Both Pfizer and Moderna have said it will be months before they are able to ship a vaccine that specifically targets the variant. Leong said that’s all well and good, but it’s not especially practical, given how fast the virus spreads and its ability to bypass existing vaccinations.

“We won’t be able to rush out the vaccines in time, and by the time the vaccines come, practically everyone will be infected [with] Omicron given this high infectiousness and transmissibility,” he said.