Sweden's chief epidemiologist Dr Anders Tegnell said Covid-19 vaccine may be developed in 2020, but its production will only start by the end of 2021.
In a webinar organized by Public Health Foundation of India, Tegnell, who is also the architect of Covid-19 Sweden's lockdown-lite, said: "To reach full herd immunity to stop the disease and may be get rid of the disease in the long term, by certain you need a vaccine.
"Vaccine may be developed in 2020, but the production will start maybe by the end of 2021."
He added people do get immunity from Covid-19. "We can tell this from four-five months of experience, and from our Swedish experience, we can say that we do not have a single person who has contracted the disease twice.
"There are very few reports, even internationally, people getting it more than once. We have a very strong system in Sweden, to identify if a person has disease twice," said Tegnell.
Explaining the aspect of immunity against the viral infection, Tegnell said that for how long the immunity will last, it has not been established yet; it may last for months and maybe for years.
He insisted that herd immunity is a complicated matter, but already with levels of immunity of the population, which is much lower than the threshold of the herd immunity would affect the speed of the spread.
Citing the herd immunity in Stockholm, he added that at least 1/5th of the population in Stockholm is immune by now, and it's apparent from the decrease of spread of the infection. "This will cut down on the spread of the disease considerably," he added.
He added that Covid-19 will stay for a long time, which means there should be some kind of sustainable response, and part of this will be, of course, the number of immune people in the population.
Detailing the secondary rate of attack of disease, where a family member infects others in the family, Tegnell said: "We see a fair amount of spread within families.
"Lot of people get disease very mildly and you only catch them if you do PCR on them. From one case of severe disease you may have 70 to 80 people with mild disease. The number of people we do not recognize is very high."
Responding to the query, why no masks in Sweden, Tegnell said "We fairly know for certain that masks do not protect you from getting ill outside of the hospital, because the kind of mask you use will not stop the virus from entering your respiratory tract. It might have some effect on you of infecting other people when you are sick."
He added that in Sweden, people are told it is better to stay home when sick rather than wear the mask. "As many other countries we are quite hesitant about the level of evidence with a mask....There are also handling issues, you should know how to handle masks....In Sweden wearing a mask will cause more problems than benefits.