There are two main factors that determine the potency of a pandemic: 1) How contagious the virus is; and 2) how potent the virus is.
I have commented often on COVID-19’s basic reproductive ratio or R0.
Potency is more difficult to quantify. There are many factors. The duration of the illness. The percentage of the population that requires hospital care. The number of people that die from the pandemic.
So far, the data seems to indicate that COVID-19 is a very contagious virus with moderate severity. I have been asked repeatedly to explain why hospital systems are so overwhelmed and there are so many deaths in areas where there are severe outbreaks if the virus is not especially deadly.
I want to show people why the R0 rate is a far more important factor than potency in determining if healthcare systems are overwhelmed and the death toll is high.
I have heard it said that COVID-19 is 20 times as deadly as the seasonal flu. As I mentioned before, this was based on the original data out of China (spotty, at best) and the faulty math of comparing COVID-19 deaths divided by positive test results for COVID-19 while using deaths divided by total estimated flu cases. Still, for the sake of this example, let’s assume those numbers are correct, that COVID-19 is exactly as contagious as the flu, but 20 times more potent in terms of hospitalizations and deaths.
Using flu seasonal contagion level of R0 1.3, after 10 transfers, 13.79 people will have the virus.
For the flu, it is estimated that 1% of the population that gets the flu is hospitalized and 0.06 – 0.15% die of complications.
For COVID-19, lets assume that 20% of the population that gets the virus is hospitalized and 3% die from complications.
Basically, after 10 transfers (1.3 to the 10th power), there are likely NO deaths from either the flu or COVID-19 at 20 times the potency of the flu. There has been some increase in hospital patients, but on a level that the hospitals can likely easily handle.
Now, lets run this exercise with COVID-19 being twice as contagious as the flu (R0=2.6) but with exactly the same hospitalization rate and death rate as the flu.
The projections at just twice the contagion level for COVID-19 versus the flu show numbers 5120% (51.2 times) higher for deaths and hospitalizations then when compared to when COVID-19 was 20 times more potent than the flu with the same contagion level. Hospital beds are filling up with patients. More people are projected to die (21.18) than if there was 100% death rate for COVID-19 with the same R0 level as the flu (13.79). Startlingly, doubling the R0 rate of the flu has over 500 times the impact on hospitalizations and deaths as doubling the severity of the flu.
This is just an exercise to show why the R0 rate of COVID-19 is the driving factor behind this pandemic. Both contagion level and potency will vary from the flu to some degree (and change over time). If the contagion level is high, as we are now seeing, and COVID-19 is only slightly more potent than the flu, that just compounds the issues we already have from the R0 rate being so high.
Panic is another huge factor in overwhelming the health system. It is estimated that only 1 in 4 of the people that go to the hospital for COVID-19 actually have it. That 141.17 figure shown above becomes 564.68 people presenting themselves at the hospital when they would normally only get 0.14 during flu season. That is a rate no medical system can handle.
While there are many factors that interact and play a part in the severity of this process, I think it’s important to know that the R0 rate is the main factor driving this pandemic at this time. The R0 will steadily decrease as more people have the disease and, hopefully, as weather conditions lower the transfer rate of the virus. Understanding that COVID-19’s potency will pose little threat for most individuals can help reduce stress and keep people from panicking and overwhelming the healthcare system unnecessarily.
Knowledge is power.
Stay safe, stay strong!