May 12, 2020
Stay Home, Stay Healthy Updates from Skagit County
Public Health reported one new laboratory confirmed case of COVID-19 today. Daily updates and total case counts are available at http://www.skagitcounty.net/coronavirus. Case counts are updated at 4 p.m.
What is R0 (pronounced R-naught) and why is it is so important?
For the last several months, public health and government officials have been talking about a mysterious value called “R-naught.” Written as the symbol R0, R0 is an important concept in epidemiology and is crucial to public health planning during an infectious disease outbreak, such as COVID-19.
R0 is the reproduction number of a virus, meaning it is a measure describing the intensity of an infectious disease outbreak. In other words, R0 defines how many susceptible people, on average, a single infected person is likely to infect during their contagious period (Susceptible means not previously immune). So if one person is infected, and they are likely to infect at least three other people, then the R0 would be 3. For example, before widespread vaccination was available, measles had an R0 of 12-18. This meant that one infected person would infect 12-18 additional susceptible people. Actually, the 2011 movie Contagion did a great job of explaining this concept.
Research establishes the basic R0, looking at the collective evidence for how many susceptible people are expected to be infected when exposed to an infectious person. The basic R0 is a characteristic of the virus. However in reality, the number of people who get infected depends on the specific situation. This is referred to as the effective R0. The effective R0 will change based on variables within the exposed population like immunity, the setting in which individuals were exposed, population density, demographics, climate factors, nutritional status, socioeconomic status, and more.
Effective R0 is why practicing good social distancing and hygiene is so important. Reducing the number of in-person contacts within a community can drastically reduce the effective R0 number. Being vigilant about good hygiene practices, like washing hands frequently, not touching your face and keeping your living spaces disinfected can also help reduce effective R0. Getting effective R0 below one will slowly reduce the number of cases in a community and allow us to begin returning to our normal day-to-day lives.
Governor Inslee’s Safe Start plan uses several metrics to evaluate safely moving between phases of the plan, but at the core of many is effective R0.
This is the variable that you can help influence. While State and local health providers continue to build testing, contact tracing and isolation/quarantine capacity, you should continue to stay strong, stay home and stay healthy. Together we can reduce effective R0 and get back to our normal day-to-day as soon as possible.