The young and healthy may have to wait years before they can be vaccinated against Covid-19, a top World Health Organisation official has said.
WHO chief scientist Soumya Swaminathan's comments show the pandemic's effects may last well beyond a vaccine becoming available and measures such as travel restrictions could last years.
There are dozens of vaccines in clinical trials in many countries and hopes are rising for inoculation to begin this year, but Ms Swaminathan said mass shots were unlikely.
Even if a successful vaccine that is safe and effective were approved, the task of making billions of doses is colossal.
"Most people agree, [it should start] with healthcare workers and frontline workers, but even there you need to define which of them are at highest risk, and then the elderly and so on," Ms Swaminathan said.
"A healthy young person might have to wait until 2022."
But even producing a vaccine is proving challenging.
Two experiments, from Johnson & Johnson and AstraZeneca's US trial, have been paused after safety concerns this week, in a setback for the global effort.
But equally, letting the infection spread and hoping to achieve “herd immunity” was unethical and would lead to unnecessary deaths, Ms Swaminathan said.
"People talk about herd immunity," she said. "We should only talk about it in the context of a vaccine.
"You need to vaccinate at least 70 per cent of people to really break transmission."
And the world must not be complacent because the death rate was decreasing. As cases continue to rise, the number of dead will follow.
New cases are hitting 100,000 daily in Europe. Nearly 20,000 infections were reported in Britain, while Italy, Switzerland and Russia were among the nations with record case numbers.
Iran has had three days of record infections and India is on course to have the world’s worst death toll.
While deaths globally have fallen to about 5,000 a day from April's peak of more than 7,500, Ms Swaminathan said, cases are rising in intensive care units.
"Mortality increases always lag behind increasing cases by a couple of weeks," she said at a WHO social media event. "We shouldn't be complacent that death rates are coming down."
More than 39 million people have been reported infected globally and 1.1 million have died.
– with reporting by agencies
