GENEVA: The World Health Organization chief hailed Monday "encouraging" news about Covid-19 vaccines but voiced serious concern about surging cases in many countries and insisted that complacency was not an option.

"This is no time for complacency," WHO chief Tedros Adhanom Ghebreyesus told a virtual press briefing.

"This is a dangerous virus, which can attack every system in the body. Those countries that are letting the virus run unchecked are playing with fire," he said.