The doctor advising the president of the European Commission on its Covid-19 response said he "wouldn't be surprised if close to a billion people have been infected" with the coronavirus.
This figure is far higher than the official case count of 124.7 million worldwide, and double the number of people who were infected with the 1918 Spanish influenza.
Dr Peter Piot, who is also director of the London School of Hygiene and Tropical Medicine, said vaccines would dramatically reduce deaths and hospital admissions, but coronavirus would continue to circulate for years to come.
Experts have long said that it is far more widespread than case counts suggest.
The real figure has been difficult to determine, in part because up to a quarter of coronavirus patients are asymptomatic, the US Centres for Disease Control and Prevention said.
This means people may not know they even had Covid-19, increasing the risk of infecting others.
But an accurate count of cases is critical to controlling the pandemic.
"No country is safe unless every country is safe," Dr Piot said on Tuesday, at an event hosted by the Dubai Future Foundation.
"This is not just a moral issue. As long as the virus is circulating anywhere in the world, no one is safe."
The expert, who co-discovered the Ebola virus in 1974 and led research into HIV-Aids, said the biggest obstacle now was producing an adequate number of vaccines.
"Companies are used to producing millions of vaccines but not billions," Dr Piot said.
But seeking to eradicate Covid-19 "is not necessary", he said.
Instead, over time, people should think of it as seasonal influenza.
How many people are vaccinated and how long people are immune before they can be reinfected are two questions that will determine the longer-term impact of the global pandemic, Dr Piot said.
Covid-19 has been shown to affect every organ of the body and can have lingering symptoms. Both factors are set to add to the burden of the healthcare system in the longer term, Dr Piot said.
"Going back to normal as before is an illusion," he said.
When you look at future scenarios, there may be outbreaks every year or every other year, but thanks to vaccination there will be much lower mortality rates, he said.
Herd immunity, Dr Piot said, would be challenging to achieve because of seasonal variations and the mutations and variants that are already being observed in different parts of the world.
This means there will always be new viruses to confront, he said.
"Only one human virus has ever been eradicated and that is smallpox.
"That took a long time. We should aim for that but it's going to take a while."
