Predictions about the course of COVID-19 over the coming weeks and months are flying around like bats out of hell. Their authors rely on fancy models that take years to master.
In a letter to shareholders on Feb. 27, 2009 Warren Buffett wrote that “investors forget to examine the assumptions behind the symbols. Our advice: Beware of geeks bearing formulas.”
The same is true here. We all need to understand what’s happening so that we can make sound decisions about who is a nutcase, who is hopelessly abstruse, and who knows what is likely to happen and has sound suggestions for intervention. There are good reasons that we want to know what will happen over the next two weeks. Is the threat from COVID-19 overblown? Is this going to be as bad as the 1918 Spanish flu pandemic? If we can narrow this down, we, the public, will have a better idea what we want from our public officials.
The first issue is why new COVID-19 cases in the U.S. grew from 7 on March 1 to almost 20,000 four weeks later, on March 29. In the U.S. during the first 25 days of March, one number explains the rapid spread of the virus. On average over each of the first 25 days of March, there were 31% more new COVID-19 cases in the U.S. than there were the day before.
We had 307 new cases on Wednesday, March 11. On March 12, there were 396 new cases, which was close to 1.31 times the 307 cases from the day before. If we multiply 307 by 1.31 fourteen times rather than just once, we get an approximation for the new cases on March 25: that is 307 x 1.3114 = 13,456 new cases. The actual number of new cases that day was 13,388.
This rapid and consistent growth continues until the cycle of transmission of the virus is broken. With no vaccine, we can only break that transmission by social distancing, so that the virus cannot jump from host to host.
The virus on average gets passed from each infected person to more than two other people. When people stop interacting at close range, and touching surfaces where infected people have left the virus behind, the virus stops being transmitted to an exponentially increasing number of people. Then the rate of growth of the cases slows rapidly.
On average it takes about seven days from infection to being sick enough to seek a test, and it has been taking about three days to get test results, so the falling rate of transmission that we’ve seen in recent days is the result of social distancing undertaken 10 to 12 days ago. Fortunately, that slowing of the growth rate is now occurring in Texas, across the U.S., and in many other nations.
Over the past week, the growth rate of new cases in the U.S. has fallen to about 12% per day. The change in new case growth from 31% per day to 12% new cases per day is very good news, but we must keep fighting to get the growth rate of new cases to zero and below, so that the number of new cases contracts. If the growth rate were to stay at 12% per day, we would have 100,000 new cases per day and 900,000 total cases in two weeks. We must completely break the cycle of virus transmission or it will break out into the entire population.
It looks like we may reach peak daily cases within a few days. But when daily cases peak, a new problem will be upon us.
As in Italy and China, when the new cases peak, they will bounce around at that high level for about a week before they start to decline. A Chinese study by Fei Zhou and others in Lancet found that COVID-19 patients that require hospitalization had a median stay of 11 days in the hospital; those who required ICU care spent eight days there before recovery or death.
The greatest number of cases will come in about a 10-day period that will begin soon. About 12% of those cases will require hospitalization, almost half of those will require an ICU bed. Doctors and nurses and other hospital staff will become infected, fatigued, and traumatized by watching helplessly as many patients die. Many patients who survive will likely have lung tissue damage for the rest of their lives. Law enforcement officers too are at risk, due to often unavoidable contact with or proximity to people, some of whom may be infected. Other people are at risk because they are providing critical services. The rest of us should take steps to relieve the pressure on the health care system, health care providers, and others who put themselves at risk to meet our critical needs.
By Steven Gjerstad
Dallas Morning News.