New Delhi, World Health Organization (WHO) chief scientist Soumya Swaminathan on Thursday said that young and healthy people may have to wait till 2022 to get the Covid-19 vaccine.

Swaminathan also stressed that health workers and those at highest risks should be prioritised.

She indicated that, despite the many vaccine trials being undertaken, speedy, mass shots were unlikely, and organising who would given access first in the event of a safe vaccine being discovered was still being worked on.

"Most people agree, it's starting 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," Swaminathan was quoted as saying to The Guardian.

"There will be a lot of guidance coming out, but I think an average person, a healthy young person might have to wait until 2022 to get a vaccine," she added.

Swaminathan hoped there would be at least one effective vaccine by 2021 but it would be available only in "limited quantities".

Swaminathan also warned against complacency about the virus death rate, saying with the increasing number of cases, mortality would also rise.

"Mortality increases always lag behind increasing cases by a couple of weeks. We shouldn't be complacent that death rates are coming down," WHO's chief scientist said.

Meanwhile, the Union Health Ministry on Thursday said the country's doubling time of Covid-19 cases has sharply increased to 70.4 days from 25.5 days in mid-August, which is nearly thrice the time being taken earlier.

"This indicates a substantial fall in the daily new cases and the consequent increase in time taken to double the total cases," the Ministry tweeted as India recorded a spike of 67,708 Covid-19 cases and 680 deaths in 24 hours, as the tally mounted to 73,07,097 cases.