Question 3. How Contagious is COVID-19? [Quorvita]

A. What is Ro?

Ro (pronounced R sub naught) is a measure of the reproduction ratio of a disease.  For example a Ro of 2 means that one individual infects 2 others and each of those people infect 2 more, and so forth.  The exponential growth gets out of control in a short amount of time. 

One problem with Ro is that this ratio requires knowing the number of actual infections.  The only numbers currently known are confirmed infections, i.e. those people who have been tested.  Currently there is no way to know the actual infection number without a large statistical analysis using random sampling techniques. These studies are rarely done. 

Multinational antibody tests have indicated that the actual number of COVID-19 infections can be anywhere from 7 to 85 times higher than the number of confirmed cases.  This means that the speed at which it is spreading is very high.  It also means that the death rate is much lower. 

B. Is There Another Way to Determine Ro?

Outside of a statistical analysis, it’s possible to determine Ro based on the slope of the curve which plots daily or weekly hospitalizations or deaths.  This data is then compared to previous pandemics to yield a relative Ro.  However, this method requires a substantial amount of data and the pandemic peak must be near or ascertainable.  Using this analysis showed COVID-19 to be roughly 2.5 times higher than the 2018 influenza virus.

C. What is Herd Immunity?

Herd immunity is a logical assumption that at some point a virus cannot spread any further because most of the cattle in the herd have developed an immunity.  The virus simply dies out before finding another host to infect.  This is the main reason why we have flu seasons rather than one constant contagion. 

Herd immunity is an interesting discussion, because there is never a specific percent associated with a specific virus.  Herd immunity varies for each environment, location, weather condition, time period, and for hundreds of other factors.  As an example, the herd immunity percent for a bunch of cattle trapped in a coral is vastly different from the immunity associated with cattle roaming the prairie.  But, the concept does exist and is an interesting topic. 

D. What Crashed the Health System.

The hospitals and health system were stressed in New York, Italy, Spain, and many other nations for several reasons. The short answer is that all hospitals and health care systems are set up based on economics. There is no economic reason to plan for pandemics that occur roughly once every 20 years. It would bankrupt any health care system to build hospital rooms that would lay empty for 19 years.

However, when COVID-19 struck, the speed at which the U. S. Federal Government constructed emergency hospital facilities, with medical staff on standby, was so successful that it may well form the model on how to handle hospital overflow burdens in the future.

If there is a silver lining, it is that pandemics are probably the greatest motivating factor in improving the health care system. The Spanish Flu was the primary reason antibiotics were developed. The small pox pandemic killed millions, leading to the development of a vaccine. Polio is on the verge of being eradicated. Measles killed millions, but is now considered eliminated in North, Central, and South America.


COVID-19 is very contagious.  It is about 2.5 times more contagious than the normal influenza virus.  This means that the reproduction ratio (Ro) could be 5 to 6, which can lead to the presence of the virus going from sporadic to widespread in a few weeks. 

Overburdening of the health system is a normal consequence of pandemics. It is the prime motivating force for the advancement of medicine.