Is the delta variant more contagious than chickenpox?

Some have said that the delta variant of SARS-CoV-2 is as easily transmitted as chickenpox. However, these statements are not quite accurate. Contagiousness is calculated with the statistic R0, pronounced R-naught, which represents the average number of people that a single, sick individual will infect. 

How does the R0 of the delta variant of COVID-19 compare to other infectious diseases?

The delta variant has an estimated R0 of 7 and the original strain of COVID-19 has an R0 of 3. By comparison, Ebola virus is less contagious with an R0 of 2, and chickenpox is more contagious with an R0 of 10. See the infographic below for the R0 of other diseases.

Source: The Lancet (1918 flu, SARS), University of Michigan School of Public Health (COVID-19, ebola, measles), Johns Hopkins University School of Public Health (chickenpox), Proceedings of the National Academy of Sciences (HIV), Tom Wenseleers at the University of Leuven (COVID-19 delta variant), Australian Government Department of Health (mumps). Credit: Michaeleen Doucleff, Alyson Hurt and Adam Cole/NPR. Icon by Gerard Higgins/The Noun Project. Published in NPR.

What is the impact of a higher R0?

Although the difference between the R0 of delta and the original virus may seem small, the delta variant is able to infect many more people. For example, with an R0 of 3, the original COVID-19 variant could infect 27 people in 3 rounds of transmission (3 x 3 x 3). However, with an R0 of 7, the delta variant could infect 343 people in 3 rounds of transmission (7 x 7 x 7). That’s a difference of 316 individuals infected!

While the delta variant is not quite as infectious as the chickenpox, it still is much more contagious than the original COVID strain that started the global pandemic. Receiving a vaccination is the best way to reduce your risk of infection and drastically lower your risk of hospitalization with COVID-19.

Last update: August 21, 2021, 03:00pm ET

Science review: SGB, AKM, ERS