I spend my time looking at data, plotting data, figuring out what the data signifies. In order to understand the data I try to make mathematical models with parameters that make sense to me and I fit these models to the data.
The corona virus is giving us a lot of data nowadays. Looking at graphs in logarithmic scale is useful. Today it tells me that the USA still has had no effect of their social distancing measures on the number of persons tested positive. Why? Because a straight line in logarithmic scale means that the growth is exponential which means that each new person infected on average transmits the disease to the same number of new persons as before. That is, no effect of social distancing. If this trend does not break in the coming week there will be 300 000 people in the USA tested positive. That is 1 out of every 1000 American. That is the same fraction of the population that currently has tested positive in Italy. But in Italy they broke the exponential trend 2-3 weeks ago. The last few days they are more or less on a linear trend, meaning that they have the same number of new cases every day.
We also hear that Italy is struggling. Right now the number of new cases daily in Italy is 1/10000 of the population. In order to reach “herd immunity” (60% of the population gets the disease and become immune) Italy would have to keep going with the same number of new cases every day as today for 16 years!! For a short period “herd immunity” was the UK goal for managing Covid-19. No wonder they changed strategy…
Of course Italy is trying to fight the spread and make the number of cases go towards zero like in China and South Korea. So in middle and high income countries in Europe, America and Asia we will probably be able to win this fight. But what if there are a number of countries in the world that because of war, poverty or a weak state, are not able to put in the resources to stop Covid-19? Then they will move towards 60% “herd immunity” and Covid-19 will become an endemic disease.
“Endemic” means that it is a disease that keeps living in the world’s population like swine flu, tuberculosis, polio, etc., and it will keep coming back to infect everyone who is not immune. We don’t care so much any more that the swine flu is endemic because “only” 0.1% die from it. Although we do not have real numbers to calculate the mortality rate of Covid-19 the reports from Italy seem to suggest that we do not want to have Covid-19 sloshing around the world in the years to come as an endemic disease.
Unless we get a vaccine… So how much will the vaccine cost? Which countries will be able to afford immunizing their entire population? How many will refuse taking the vaccine? Well, in a few months time when the current crisis has slowed down we will probably be discussing vaccines and how for long we should ban incoming foreigners from hard hit countries.
But of course, I’m only a physicist looking at data. I’ve never studied epidemiology, medicine or social sciences…
Dag Kristian Dysthe 