How many will be infected?
When will it peak?
What can we do to prevent getting sick and reducing the spread of the virus?

Step by step, the novel coronavirus has upended the world’s social and economic fabric since it was first identified in China last year. Nearly every country in the world has by now shuttered schools and businesses, restricted travel, closed borders, canceled entertainment and sports, and encouraged people to stay away from each other. The pandemic is global and no one is spared. Leading politicians, sports stars, celebrities and your next-door neighbor are all among those testing positive for the virus.
The situation in Sweden is calmer than in many places. Yes, the country has 1,301 cases of COVID-19 as we write this (March 18) and ten people have died, most of them elderly or immunocompromised, but the borders were not closed until all of Europe’s borders closed on March 19. There’s a shortage of some health care equipment such as hand sanitizers.


The decisive factor for the spread of any virus is what scientists call the basic reproduction number, or R: how many more will be infected by one infected person. For the coronavirus scientists now waver between two and 2.5, although we’ve also seen numbers as high as five in early news reports. Professor Tom Britton at Stockholm University uses a mathematical model to explain how fast the coronavirus is likely to spread. Listening to him is enlightening—and makes me wash my hands even more often, disinfect surfaces on a regular basis and stay away from groups and meetings.

Let’s take a look at a highly hypothetical case, not specifically based on the coronavirus. If everyone in a fairly homogenous society is susceptible, that is, no one is immune, no one has been vaccinated (which is the case with COVID-19) and there’s been no change in behavior, and let’s for the sake of simplicity assume the number of people one infectious person infects is three. (The basic reproduction number is 3)

If your neighbor starts his day being infected

In recent weeks, after 20 years as a mathematician, Tom Britton has become extremely popular. What everyone wants to know is: How serious will it be? We reached out to Britton to get a better grasp of what his models mean for us in the long run.

“My main area is mathematical models for the spreading of infections, and also statistical methodology for how to determine a model’s parameter values, such as R, from outbreak data. It is called “taxes” in statistical language.”

“The answer depends very much on what preventive measures are being taken, by ourselves and by the authorities. It is estimated that the reproduction number R, the number infected by a person, is 2.5 before any restrictions or measures have been implemented in a society. Then 60-70 percent will be infected. If nothing is done, this is how many people will become infected in Sweden. But if we manage to reduce the number of reproductions with different measures, of course fewer will be infected. The magic value is R = 1. As soon as we get the reproduction number below 1 with different measures, it will quickly disappear. China succeeded in this by means of very comprehensive measures, and very quickly, so that less than 1 percent will be infected in Wuhan. I am not convinced that we will be as effective in for instance Sweden.”

Using Britton’s model and our example of a reproduction number of 3, putting societal restrictions in place and thereby reducing this to 2 instead, the peak will go down by 50% - that is, 50% less people will be affected - and delay the peak with 70% - in other words, allowing the health care system to catch up.

Well, China has closed down its last coronavirus hospital. For lack of patients!
So, help each other to the extent possible in the community while still avoiding direct contact. Wash your hands often, stay inside to the extent possible, listen to the scientists and recommendations by health care professionals (forget the fake pundits)!
As for other good news,
• One patient, just released as recovered in Wuhan, was a 103-year-old grandmother.
• Apple stores in China have reopened and factories started producing again.
• The number of new cases in South Korea is going down.
• A new U.S. developed coronavirus test gives results in hours, not days
• Several U.S. patients have already recovered and returned to everyday life.
• Doctors in for instance India have experimented with a mix of medication to treat patients that seems to work.
• Researchers claim to have found an antibody against the virus; plasma from already recovered patients are used to treat others infected and the hunt for a vaccine is on all over the world. (See EU grant for Coronavirus Research)

Ulf Barslund Martensson

If you are interested in Britton’s model for the spread of a virus, we recommend you check his lecture, in English: Math of the Corona outbreak (a half hour well spent)