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How Infectious is the Coronavirus?

November 8, 2020

how infectious is COVID-19

know the r-naught

by Jamal Ross

News reports, hospitalization numbers and personal stories relayed by friends gives us an idea of how rapidly the COVID-19 virus can spread. Yet, it remains important to know how infectious the COVID-19 virus is when compared to other pandemics. The infectious nature of a virus can be expressed in a number called the R-naught(R0). The higher the R0, the more infectious a virus can become.

The R-naught is also called the basic reproductive rate. In plain terms, the R0 tells us how many individuals one per person can infect with the virus. The R0 for the COVID-19 virus was 2-3 during the early part of the pandemic. In other words, one person with the COVID-19 virus will infect 2-3 other people. Afterwards, each of those 2-3 others can go on to infect 2-3 people each. This may not seem like a large number, but the multiplication occurs quickly and this virus can spread rapidly in our communities. Let’s look at how the R0 for COVID-19 compares with other viruses.

The COIVD-19 virus is one of the most infectious viruses we have seen in this century. For comparison, the R0 for the 1918 flu pandemic was 1.7. Also, the first outbreak of coronavirus in 2003 with SARS-CoV-1 had a R0 of 2.4. The 2009 H1N1 influenza pandemic had a R0 of 1.7. On average we can say the R0 for the COVID-19 virus is 2.5. (1) Additionally, what makes the COVID-19 virus particularly troubling is that it has the ability to spread immediately once symptoms begin or even during the incubation period.

Any measures that can decrease the spread of COVID-19 can decrease the R0. Therefore, preventative measures sure as social distancing, wearing a mask and isolating yourself if you have been exposed to or infected with the COVID-19 virus can help bring the R0 near zero and hence decrease the spread.


  1. Petersen E, Koopmans M, Go U, Hamer DH, Petrosillo N, Castelli F, Storgaard M, Al Khalili S, Simonsen L. Comparing SARS-CoV-2 with SARS-CoV and influenza pandemics. Lancet Infect Dis. 2020 Sep;20(9):e238-e244. doi: 10.1016/S1473-3099(20)30484-9. Epub 2020 Jul 3. PMID: 32628905; PMCID: PMC7333991.

Jamal Ross

Dr. Jamal Ross is an internist and pediatrician who possesses a passion for prayer and preventative medicine. He has worked in the fields of primary care and hospital medicine.

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