The virus that causes COVID-19 could gain a permanent place in the population without global vaccination, warns the U.S. government’s top infectious disease expert, Dr. Anthony Fauci.

“We’ve got to get the whole world vaccinated,” Fauci told reporters Monday during the International AIDS Society’s COVID-19 conference. “If we don’t get a global effort, without a doubt, this is not going to go away.”

Vaccine supply greatly lags demand, and access has been uneven around the world. Recent results on two candidate vaccines suggest they may work less well against some virus variants, especially one first detected in South Africa, but they are still extremely good at preventing serious illness or death, Fauci said.

The impact of vaccines on the pandemic depends not just on how well they work but how quickly and completely they’re distributed, he added. Vaccines and public health measures such as wearing masks, keeping social distance, avoiding crowds and washing hands are the best way to prevent more cases and further mutations of the virus, he and other experts at the conference said.