The head of the World Health Organization says experts are continuing to research the Omicron coronavirus variant and has called for vaccination of high-risk people in all countries.

WHO Director-General Tedros Adhanom Ghebreyesus spoke at a news conference on Wednesday. The WHO designated the newly emerged strain as a "variant of concern" last Friday.

He said the WHO is learning about the variant, but that there is still more to grasp about "its effect on transmission, severity of disease and the effectiveness of tests, therapeutics and vaccines."

Tedros said experts across the world are evaluating emerging evidence to answer those questions.

He called on countries to swiftly vaccinate high-risk and vulnerable people, including the elderly, and provide vaccines to developing nations.

The WHO's technical chief for coronavirus response, Maria Van Kerkhove, said the organization expects to have more information on transmission "within days, not necessarily weeks."