COPENHAGEN (AP) — Nearly 36 million people in Europe may have had long-lasting health problems from coronavirus infections they got during the first three years of the COVID-19 pandemic, the World Health Organization’s regional director said Tuesday.

Dr. Hans Kluge said “long COVID” remained “a complex condition [that] we still know very little about” and that is “a glaring blind spot in our knowledge.”

“Unless we develop comprehensive diagnostics and treatment for long COVID, we will never truly recover from the pandemic,” Kluge said, reiterating that older adults, people with underlying medical conditions and others with weakened immune systems should continue getting vaccinated.

While most people recover from COVID-19 within a few weeks after infection, some people have reported experiencing ongoing fatigue, shortness of breath and brain fog.

WHO’s Europe region covers 53 countries from Ireland to Uzbekistan with a combined population of more than 900 million. Statistics from University of Washington researchers indicate that about one in 30 of the region’s residents have experienced “long COVID” in the past three years, Kluge said.

The origin of the virus that triggered once-unthinkable lockdowns, upended economies and killed millions of people worldwide has not been pinpointed.

Last month, the World Health Organization said that COVID-19 no longer qualifies as a global emergency. The announcement was made more than three years after WHO declared the coronavirus an international crisis. The U.N. health agency said that did not mean the pandemic had ended, noting recent spikes in cases in Southeast Asia and the Middle East.

In Europe, “COVID-19 exploited an epidemic of diseases, including cancers, cardiovascular disease, diabetes and chronic lung illnesses, which account for 75% of mortality,” Kluge said.

“Those with such underlying conditions were, and still are, far more vulnerable to severe forms of COVID-19,” he added.