At a press conference this afternoon, Swiss federal government officials advised the cantons to effectively close schools.
According to Alain Berset, children are to stop going to school, however, the cantons must make the final decision. Schools can stay open if they have fewer than 50 people in them, a measure designed to give teachers more scope to facilitate home schooling.
Vaud, Fribourg and Ticino have already closed schools, according to RTS.
Berset said the decision was prompted by advice from the European Centre for Disease Prevention and Control, the rapid spread of the infection in Ticino and decisions being made in neighbouring countries.
Closing schools reduces human contact and that reduces the spread of disease. However, to be effective, it needs to be done before the infection level reaches a critical point, and that point might have been passed.
On average, there are 5.1 days between catching the virus and the onset of symptoms so the number of confirmed cases is the actual number of cases 5.1 days ago. This means in the growth phase of the spread confirmed cases are like the tip of an iceberg.
5.1 days might not seem that long. But if you look at the chart above from a WHO report on COVID-19 in China, which shows new coronavirus cases from 8 December until 20 February for all of China, you’ll see there are orange and blue bars. The orange bars represent confirmed cases. The blue ones are actual cases – these are calculated by counting backwards from when the symptoms appeared, something that can only be done in retrospect.
On 24 January 2020, there were around 1,000 confirmed cases. This is the sum of all the orange bars up to and including that date. Now add up all of the blue bars up to and including 24 January 2020 and you’ll arrive at a cumulative total of more than 16,000 actual cases. In the early phase of the epidemic in China when there were 1,000 confirmed cases, there were 16,000 actual cases, 16 times the number of confirmed cases. They just couldn’t see all these cases because most patients hadn’t shown symptoms and tested positive. If Switzerland is at this point then it will have a similar number of cases.
The next question is where Switzerland is on the epidemic curve, a curve that shows the number of infections over time. We have searched government websites for this information but cannot find any data. Instead we did some hypothetical modelling.
If every person with the disease infects an average of two people then the disease has an Ro of 2. A WHO report on COVID-19 in China estimates an Ro of between 2 and 2.5. Other Ro estimates for the virus range from 1.4 to 3.9.
The chart below shows the rise in cases at an Ro of 2. At the beginning the rise is slow. However, then it rises steeply. From 1 to 12 in the chart below the number barely changes. From 13 onwards the rise is steep.
It is important to note that the numbers on the x axis are not days. Ro numbers are independent of time and no time span was mentioned in the WHO report. Where Switzerland is on this curve is unclear.
So, if Switzerland has 16,000 actual cases, which is likely, and it has entered the steep part of the epidemic curve, which is possible, the number of cases could be set to take off rapidly.
WHO report on COVID-19 in China (in English)