A fertile breeding ground for new COVID-19 variants is being created by a "toxic mix" of low vaccination and low testing rates, the World Health Organization (WHO) warned on Wednesday.

The WHO said measures to stop the globally-dominant Delta variant, first identified in India, would also help hinder Omicron, the new variant that was first discovered last month in southern Africa and which has since caused concerns in countries around the world.

WHO chief Tedros Adhanom Ghebreyesus called on countries to boost their public health and increase their social measures to control the spread of COVID-19.

He insisted that nations need to make sure that high-risk and vulnerable individuals are fully vaccinated "immediately".

Tedros reminded that while global attention turns to Omicron, the world was already struggling with the "highly transmissible, dangerous" Delta variant, which currently "accounts for almost all cases" globally.

"We need to use the tools we already have to prevent transmission and save lives from Delta. And if we do that, we will also prevent transmission and save lives from Omicron," Tedros told a press conference.

"But if countries and individuals don't do what they need to do to stop transmission of Delta, they won't stop Omicron either, adding, "globally, we have a toxic mix of low vaccine coverage, and very low testing -- a recipe for breeding and amplifying variants."

Tedros recommended that "we continue to urge countries to... ensure equitable access to vaccines, tests, and therapeutics all over the world."