Health experts still don't know if the new variant is causing milder COVID-19, but more indicators are emerging.
The World Health Organization's top official in Europe said 89% of those with confirmed omicron infections in the continent reported symptoms common with other coronavirus variants, including cough, sore throat, fever.
The variant has mostly been spread by young people in their 20s and 30s in the region, Dr. Hans Kluge added.
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Although much remains unknown about omicron, Kluge said it appears to be more infectious than previous variants.
"The sheer volume of new COVID-19 infections could lead to more hospitalizations and widespread disruption to health systems and other critical services," he said.
In Southern Africa, where the variant was first detected by researchers, doctors suspect that the omicron version is causing milder COVID-19 than delta, even if it seems to be spreading faster.
Dr. Unben Pillay said his COVID-19 patients during the last delta wave "had trouble breathing and lower oxygen levels. Many needed hospitalization within days," he said. The patients he's treating now have milder, flu-like symptoms, such as body aches and a cough, he said.
Pillay is a director of an association representing some 5,000 general practitioners across South Africa, and his colleagues have documented similar observations about omicron.
"They are able to manage the disease at home," he said of his patients. "Most have recovered within the 10 to 14-day isolation period."
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And that includes older patients and those with health problems that can make them more vulnerable to becoming severely ill from a coronavirus infection, he said.
The experts caution that it will take many more weeks to collect enough data to be sure, but their observations and the early evidence offer some clues.
This evidence is murky because many documented cases have been among people who are vaccinated and people who have prior infection, which may dramatically reduce the risk of severe illness, according to the ABC News Medical Unit.
Also, mild cases in one country may not translate to the same in the U.S. The delta variant, for example, turned out to be much more deadly in America than in the U.K., the Medical Unit reported.
Symptoms will not be the same for everyone, and the only way to diagnose COVID-19 is through testing.
The Associated Press contributed to this report.