The World Health Organization on Tuesday said the pandemic will not end as the omicron variant subsides in some countries, warning the high levels of infection around the world will likely lead to new variants as the virus mutates.

“We’re hearing a lot of people suggest that omicron is the last variant, that it’s over after this. And that is not the case because this virus is circulating at a very intense level around the world,” Maria Van Kerkhove, the WHO’s Covid-19 technical lead, said during a coronavirus update in Geneva.

New infections have increased by 20% globally over the past week with nearly 19 million total reported cases, according to the WHO. But Van Kerkhove noted that new infections that go unreported would make the real number much higher.

Dr. Bruce Aylward, a senior WHO official, warned high levels of transmission give the virus more opportunity to replicate and mutate, raising the risk that a new variant will emerge.

“We don’t fully understand the consequences of letting this thing run,” Aylward said. “Most of what we’ve seen so far in areas of uncontrolled transmission has been we paid a price for the variants that emerge and new uncertainties we have to manage as we go forward.”

Van Kerkhove said now is not the time to relax public health measures, such as curtailing mask wearing and physical distancing. She called on governments to strengthen those measures to bring the virus under better control and head off future waves of infection as new variants emerge.

“If we don’t do this now, we will move on to the next crisis,” Van Kerkhove said. “And we need to end the crisis that we are currently in and we can do that at the present time. So don’t abandon the science. Don’t abandon the strategies that are working, that are keeping us and our loved ones safe,” she said.

Read more: Fauci says it’s still an ‘open question’ whether omicron spells Covid endgame

Van Kerkhove called on governments to invest more in surveillance systems to track the virus as it mutates. “This won’t be the last variant of concern,” she stressed.

In December, a team of South African scientists published a small study that found people infected with omicron may have increased immune protection against the delta variant. A growing body of research has also found that people infected with omicron generally don’t get as sick as people infected with delta. Increased immune protection and less severe illness, taken together, could result in the virus becoming less disruptive to society, the South African scientists wrote.

However, White House chief medical advisor Dr. Anthony Fauci on Monday said it is too early to predict whether omicron will mark the final wave of the pandemic.

“I would hope that that’s the case, but that would only be the case if we don’t get another variant that eludes the immune response of the prior variant,” Fauci told the World Economic Forum’s Davos Agenda via video conference.

WHO Director-General Tedros Adhanom Ghebreysus said new infections are peaking in some countries, providing hope that the worst of the omicron wave is over. However, Tedros said no country is out of the woods yet, warning that health-care systems are still under pressure from the unprecedented wave of infections.

“I urge everyone to do their best to reduce risk of infection so that you can help take pressure off the system,” Tedros said. “Now is not the time to give up and wave the white flag.”

The WHO has repeatedly warned that unequal distribution of vaccines worldwide has led to low immunization rates in developing countries, leaving vast populations vulnerable to the emergence of new variants. The WHO had set a target for every country to vaccinate 40% of its population by the end of 2021. However, 92 countries have not achieved that goal, according to the WHO.

“This pandemic is nowhere near over and with the incredible growth of omicron globally, new variants are likely to emerge, which is why tracking and assessment remain critical,” Tedros said.