Flattening the Curve - Variable Outcomes

We've all seen the nice graphic asking us to "Flatten the Curve". It's a positive goal to set, and makes people feel good about their efforts, but how realistic are the two outcomes we've been shown? Below is the Mayo Clinic's version of the curve.

As encouraging as this chart looks, the result in the blue is not likely given the current rate of infection growth, and mathematically it's not possible if we maintain daily exponential growth.

According to the growth rates provided by www.CovidTracking.com, the Coronavirus infection rate has been growing at about 36.8% per day. That exponential growth rate is what's scaring our nations leaders and the reason for the massive lock downs. There are two numbers in particular that scare the experts, and we should pay close attention to how they strain the medical system. According to the NY Times, there are 172,700 ventilators in the US. According to the WSJ, 5% of Covid19 patients in Germany were severe enough to need a ventilator. The basic math says that we have to stop the Coronavirus at 3,454,000 positive cases in the US before we run out of ventilators. Of coarse the distribution of those machines throughout the system isn't that cut and dry, and some companies are racing to build more ventilators. We also don't know for sure how many US patients will need ventilators.

At a growth rate of 36.8% daily infections in the US, we have until April 6th until we run out of ventilators. That's 15 days from today, and the reason our country is placing shelter-in-place restrictions, travel bans, etc... We have a very short amount of time to stop the exponential growth. Even at 10% daily infection growth, we would only have until May 17th (57 days) to reach 172,700 ventilators.

According to a doctor I talked to (who wished to remain anonymous), anyone that needs a ventilator, that doesn't get one, would die. He admitted that much of the data is anecdotal because we're using data from different countries with varying quality of health care, and we won't know the true numbers until months afterwords.

A model first offered to administrators at University of Pennsylvania hospitals, and then distributed to hospitals around the country, warned that only 1% of patients would need a ventilator, a detail that significantly alters the curve outcomes (see below) with between 2.2M patients going without ventilators at 10% daily infection growth to 3M patients going without a ventilator at 40% daily infection growth, but that assumes 100% of the population contracts Coronavirus.

So obviously the rate of ventilators per positive patient is the key factor in our medical system's effectiveness in fighting this outbreak. I doubt that the worst case scenario is possible, but if it were, we would have up to 16M patients going without a respirator, given a 5% need for ventilation instead of the 1% suggested by the Penn model which would only result in about 3 million people going without a ventilator. Again, the assumption is that these people are the most severely affected and would die without a ventilator. At this point, the 1% projection seems unrealistic given that the mortality rate in the US up until today is 1.17%, much lower than the mortality rate in China and most of Europe.

According to a WHO report on China, severe cases are defined as more than 30 breaths per min or oxygen saturation less than 93% at rest. Critical cases are defined as respiratory failure requiring mechanical ventilation, shock or other organ failure that requires intensive care. About a quarter of severe and critical cases require mechanical ventilation, or about 5% of total infections. 

Is there an upper limit to the spread of the virus? According to the CDC, this years flu season produced about 38M to 50M Americans contracting the flu between October 2019 and mid March 2020. That's between 11-15% of the US population, and although Covid19 isn't said to be "airborne", the incubation period is noticeably longer, and our immunity is speculated to be much weaker to Covid19, as most of us have had the flu before. Given those two assumptions are true, I assume it's within the realm of possibility that we could see a similar result. I also couldn't find a reliable probability for the chance Covid19 transforming into an airborne virus, but that's what happened in the Dustin Hoffman's movie Outbreak. According to CSIRO's Professor Trevor Drew, "Its mutation rate appears to be about half that of Influenza. And influenza changes enough to make yearly flu vaccine updates effective."

The good news is that as China's exponential daily infection growth rate seemed to stop all of the sudden when they hit about 81,000 infections with very little explanation why. My best guess is that China implemented severe lock-downs in a way that only a communist country could.

For that reason, I'm treating the shelter-in-place as if I'm living in a communist country, and I would be arrested for not social distancing. The two months difference between 40% daily growth and 10% daily growth could mean millions of lives, and so far we're still on a logarithmic scale of new positive infections.