The coronavirus could become endemic in the same way as HIV and populations around the world will have to learn to live with it, the World Health Organization (WHO) warned on Wednesday.
As some countries begin gradually easing lockdown restrictions, the WHO said COVID-19 may never be wiped out entirely.
"It is important to put this on the table: this virus may become just another endemic virus in our communities, and this virus may never go away. HIV has not gone away, but we have come to terms with the virus," WHO emergencies expert Mike Ryan told an online briefing.
"I think it is important we are realistic and I don't think anyone can predict when this disease will disappear. I think there are no promises in this and there are no dates. This disease may settle into a long problem, or it may not be."
However, Ryan said the world had some control over how it coped with the disease, although this would take a "massive effort" even if a vaccine were found, a prospect he described as a "massive moonshot".
More than 100 potential vaccines are being developed, including several in clinical trials, but experts have underscored the difficulties of finding ones that are effective against coronaviruses.
Ryan noted vaccines exist for other illnesses, such as measles, but they have still not been eliminated.
WHO Director-General Tedros Adhanom Ghebreyesus added: "The trajectory is in our hands, and it's everybody's business, and we should all contribute to stop this pandemic.
"Many countries would like to get out of the different measures," said Tedros. "But our recommendation is still the alert at any country should be at the highest level possible."
Ryan said "very significant control" of the virus was required in order to lower the assessment of risk, which he said remained high at the "national, regional and global levels".
More than half of humanity has been put under some form of lockdown since the coronavirus crisis began in January.
Governments around the world are struggling with the question of how to reopen their economies while still containing the virus, with some 4.3 million confirmed cases around the world, and more than 291,000 deaths.
The European Union pushed on Wednesday for a gradual reopening of borders within the bloc that weer closed because of the pandemic, saying it was not too late to salvage some of the summer tourist season while still keeping people safe.
But public health experts say extreme caution is needed to avoid new outbreaks. Ryan said opening land borders was less risky than easing air travel, which was a "different challenge".
"We need to get into the mindset that it is going to take some time to come out of this pandemic," WHO epidemiologist Maria van Kerkhove told the briefing.
'Senseless acts of violence'
Ryan also condemned attacks on healthcare workers that were linked to the pandemic, saying more than 35 "quite serious" such incidents were recorded in April alone in 11 countries.
He said the attacks were often overreactions from ill-informed communities, while others were more sinister.
"COVID-19 is bringing out the best in us, but it's also bringing out some of the worst," he said. "People feel empowered to take out their frustrations on individuals who are purely trying to help. These are senseless acts of violence and discrimination that must be resisted."
Ryan insisted finding a way to conquer the virus was a chance for humanity to take major step forward by finding a vaccine and making it widely accessible. "It's a massive opportunity for the world," he said.