B. Is There Another Way to Determine Ro?
The steepness of an infection curve is an indicator of contagion. Mortality rates may also be used in lieu of infections. As shown in Figure 5, the death rate curve for the 2018 influenza outbreak had a slope of 552 deaths/week. The slope of the influenza death rate when influenced by COVID-19 is 1388 deaths/week.
This indicates that COVID-19 is roughly 2.5 times more contagious than the influenza strain.
Figure 5 is the United States Flu & Pneumonia Weekly Deaths. The horizontal axis is the number of weeks from Sept 2015 to April 2020. The vertical axis is the weekly deaths. The Data is from CDC.
Contagion is a combination of many factors. It is not just Ro. But, since the influenza virus has the same spread mechanism as COVID-19, i.e. respiratory, Ro can function as a rough indicator. Using the Figure 5 comparison, the Ro should be roughly 2.5 times higher. If the influenza virus had an Ro of 0.9 to 2.1, then the Ro of COVID-19 could be somewhere between 2 and 5.
COVID-19 is technically an illness caused by the SARS-CoV-2 virus. But most people refer to “coronavirus” or “COVID” or “COVID-19” as the virus and the disease. In this discussion, COVID-19 is referring to both the SARS-CoV-2 virus as well as the COVID-19 disease.
The graph also shows that the upward slope of the 2018 influenza outbreak is steeper than the downward slope by a factor of 1.5 to 2.5. This means that it comes on faster and leaves slower. This is not to be confused with what is referred to as “flattening of the curve.” That is a controversial subject covered in more detail in Question 4.
How COVID-19 compares to other viral diseases is shown in Table 3 below. Information from Wikipedia. [https://en.wikipedia.org/
Table 3. This is a table of the Ro for various Viruses and the Transmission Mechanism. This information was obtained from Wikipedia.org.