According to all previous estimates, 60 percent of the population should be immune to the spread of infection. A new calculation, which is a collaboration between the Department of Mathematics at Stockholm University and the University of Nottingham, shows that fewer need to be infected before the population reaches immunity protection.
Tom Britton, professor at Stockholm University, is one of the researchers behind the new figures.
- When an infection is spread in a population, it is not spread randomly, but those who meet a lot of people are at greater risk of being infected than those who are less social.
- When immunity arises from the spread of a disease, the immunity is not uniformly spread, as when vaccinated. So when 40 percent of the population is infected, maybe the extra social is infected with 60 percent and is then more immune than the non-social, says Tom Britton.
40-45 percent can suffice for herd immunity
The model has a reproduction rate of 2.5 (when an individual infects 2.5 people on average) and this means that the herd immunity occurs at about 40-45 percent instead of 60 percent, according to Tom Britton. The results of the survey have not yet been quality checked.
- Two things that make our results likely are that another group in Liverpool have come to roughly the same conclusions. And that perhaps the most prominent epidemiologist Mark Lipsitch at Harvard has read our reports and tweeted in positive terms, says Tom Britton.
State epidemiologist Anders Tegnell tells TT that even if Stockholm reaches herd immunity in June, it does not mean that the danger is over.
- We will still have a lot of spread, but at a low level, says Anders Tegnell.
Travel in summer
At present, the Ministry of Foreign Affairs does not recommend trips abroad until June 15, but according to Foreign Minister Ann Linde (S) it will not be free for travel after that, even if travel restrictions are lifted. The Public Health Authority has said that they will announce at the end of May what it will be like in summer with travel.
- We come with a message, but what message we come with depends on the development. It's not about getting a new increase in cases in Sweden, says Anders Tegnell.