April is the month when the spread of the corona virus will be most intense. This is according to Tom Britton, professor of mathematical statistics at Stockholm University, who works with models of how infectious diseases behave in a population.

- This is such an infectious disease that over half of Sweden's population will be infected before the end of April. After that, the spread of infection will not stop, but it will go slightly slower so that about two-thirds will be infected by the end of May, he says.

Not the same risk

The calculations are based on the fact that between half a million and one million Swedes are currently infected.

- It is a fairness assessment that I would not pledge my house to. But if I could say between 250,000 and a million and a half, instead. Then I would probably dare put the house in pledge, says Tom Britton.

Stay at home in April

This means, he says, that if the elderly and at-risk groups want to stay home and avoid social contacts for only a limited time, then April is the time to invest.

- If you go out in April, maybe one in ten people is contagious. This means that you only need to meet ten people for you to run a fairly high risk of getting infected. If you do the same thing in late May or June, however, you do not run the same risk at all, says Tom Britton.

If we had taken tougher measures, would the spread of infection have decreased even more?

- In that case, we might have been able to smudge the curve even more, but there are also measures that would have affected society more drastically in the same scales. I think they found a fairly reasonable level.

"Not unreasonable"

At present, the lack of data makes it difficult to say with certainty how many will be infected at a certain time. But Tom Britton's calculations do not surprise Jan Albert, professor of infection prevention.

- What is needed is population surveys where you have looked at how many people have had the infection. Tests for it are just beginning to become available so it has not been possible to do until now and in addition it takes a while from being infected to being able to do these tests. Until this kind of data exists, there are forecasts that have a lot of uncertainty, but this forecast is not at all unreasonable, he says.

That there will be some kind of peak in April, however, seems to be a reality.

- It is right now that most people expect us to have an active spread of infection on the way up, and that it is heading towards some kind of peak. Whether it is a single peak or if there are more, we do not know, says Jan Albert.