There could soon be a day when a new COVID-19 variant emerges that will be resistant to existing vaccinations, warned the chief of the World Health Organization on Wednesday.

WHO Director-General Tedros Adhanom Ghebreyesus warned that the world was losing time in achieving higher levels of vaccination as poorer countries continue lagging behind wealthier counterparts. He warned that COVID-19 was still evolving and may soon mutate into something harder to defend against.

“As this pandemic drags on, it’s possible that new variants could evade our countermeasures and become fully resistant to current vaccines or past infection, necessitating vaccine adaptations,” he said at a press conference in Geneva.

The warning comes as the Omicron variant begins pushing COVID-19 case numbers back up across the globe. In the U.S., it is the most common variant among patients while case numbers are being driven up by new infections in the U.K., France and across Europe.

The Omicron variant is considered milder in its symptoms than the preceding Delta variant, which has not been defeated. Researchers are continuing to seek a fuller understanding of the new strain, but they warn that Omicron may be capable of overcoming resistance provided by some existing vaccines.

He also took the opportunity to excoriate what he saw as the inadequacy of international efforts to improve vaccination rates worldwide. He repeated earlier criticism of ongoing booster campaigns in more developed states as crimping global supplies for poorer states, but also slammed what he said was a "short-term nationalism" that undermines the battle against future variants of COVID-19.

"Populism, narrow nationalism and hoarding of health tools, including masks, therapeutics, diagnostics and vaccines, by a small number of countries undermined equity and created the ideal conditions for the emergence of new variants," he said. “This is the time to rise above short-term nationalism and protect populations and economies against future variants by ending global vaccine inequity.”

He issued a call to seek a global vaccination rate of 70% by July 2022.

According to The New York Times' global vaccination tracker, the rate of fully vaccinated individuals is 50%, but some continents lag behind others with Africa only having a vaccination rate of 13.2% compared to the 65% found in Europe.