The corona reproduction number R is a function of …?

The number of corona infections can roughly be modeled as N ~ R^t, where t is time1 and R is the reproduction number. The reproduction number R is the average number of new infections caused by one person infected with Covid-19.

If R > 1, the number of patients grows exponentially. If R < 1, the epidemic fizzles out.

How do people get infected? Obviously, they have to come into contact with the virus.

R is high when people are close together, indoors, and talking/singing/shouting. That explains why most infections occur at care facilities, slaughterhouses, prisons and at home2. There also seems to be a climatological effect. Sunlight, heat and humidity are correlated with a lower R. Genetic and (tuberculosis) vaccination differences between populations have been suggested to play a role.

Johannes Borgen (@jeuasommenulle) has estimated R for different countries3. You can find his methodology here.

As expected, lockdowns reduce R to below 1.

According to this map, the pandemic is still growing in Latin America, Africa and South Asia.

  1. Divided by relevant period so that t is a dimensionless number.
  2. It’s also why bars, restaurants and sports and music events are the last to reopen after lockdowns.
  3. This isn’t an easy task, as the test capacity – and so the number of infections that are observed – changes over time.

Leave a Reply

Your email address will not be published. Required fields are marked *