How contagious is the Delta variant of Covid-19? See how coronavirus can spread through a population, and how countries flatten the curve

You can see how subtle changes in social behavior or the contagiousness level of Covid-19 could affect the fight to stop it spreading.
How the coronavirus spreads in a population, and how to stop it

This interactive feature was published originally in April 2020. It was last updated on 27 August 2021, to show the Delta coronavirus variant's infectiousness.

The contagious nature of viruses and other pathogens are an important characteristic.

There are several ways to measure this. The R0, or basic reproducibility number, is a key indicator of how many cases an infected person creates.

We would expect that each new case of a disease will produce three more infections for an R0 of 3.

This does not simply reflect the disease's inherent infectiousness. It is also affected by other factors such as the frequency of infection within the population and the time of the disease. This is a situation-dependent number, meaning that the R0 may be higher in some cities than it is in others. This assumes that all people are susceptible to the disease.

Early Covid-19 behaviour studies in Wuhan found that the average R0 was between 2.2 to 2.7. However, smaller outbreaks like the one onboard the Diamond Princess had an R0 of 2.2. Other studies have shown that values as low or high as 1.5 are possible.

What does this look like? How does it compare to other diseases?