The World Health Organization (WHO) chief said the COVID-19 Delta variant, first seen in India, is "the most transmissible of the variants identified so far," and warned it has now been identified in at least 85 countries and is spreading rapidly among unvaccinated populations.

WHO director-general Tedros Adhanom Ghebreyesus said at a Friday press briefing that new variants are expected and will continue to evolve but the emergence of variants can be avoided by preventing transmission.