The New York Times reported Friday on Centers for Disease Control (CDC) worst case studies of COVID-19 in the United States.  Between 160 million and 214 million could be infected and 200,000 to 1.7 million could die.  In the same article, an infectious diseases specialist and public health expert at the University of Nebraska Medical Center, said his conservative calculations suggested 480,000 deaths.  NBC News reported last week that “The attending physician of Congress and the Supreme Court … briefed Senate staff on Tuesday afternoon in a closed-door meeting and said that he expects 70 million to 150 million people in the U.S. will contract the coronavirus…”  At least some of these reports have the qualification that this is what could happen if nothing is done to mitigate the virus.

These reports motivate the public and the government to do what needs to be done to limit the impact of the virus.  What is the likely situation if mitigation efforts are effective?  The answers are that the numbers are probably substantially smaller than the above estimates, but significantly larger than the current numbers.

To understand why, let’s start with China’s experience.  The virus jumped to humans in China several months ago, infections and deaths grew exponentially, the government stepped in with significant mitigation efforts, and the total numbers of infections and deaths have now plateaued. A study of this history reported in ourworldindata.com provides data on probability of death versus age group.  Applying this data to the age groups in the United States yields Table 1.  With the USA’s demographics, we can expect the probability of death if infected to be 1.8%.

Table 1 USA Demographics and COVID-19

Now we need to know how many people in the USA might become infected.   The recent experience of several countries bound the number.

As of March 13th, China had 80,824 confirmed cases (worldometer.com), and as Figure 1 shows, their total infections have plateaued.  They appear to be over the worst of it.  The figure also shows how the reported Daily Growth Rate has changed since late January.  The Daily Growth Rate has a couple of spikes due to the reported data settling down early on, and a change in how China counted cases in early February.  Even with these spikes, the measures China took reduced the Daily Growth by 10%, day-over-day.  This means that if one day the number of cases increased by 30% from the prior day, the next day’s growth will be down to 27%. The Curvefit to the Daily Growth Rate line in the figure reflects this 10% day-over-day reduction.  As you will see, the day-over-day reduction value is critically important to the subsequent discussion.

Figure 1 China Cases, Daily Growth Rate History and Curve-fits

South Korea took countermeasures against COVID-19 early on, and they have done extensive testing of their population.  As a result, they were able to reduce their Daily Growth Rate by 14%, day-over-day.  As a result their case count has nearly plateaued even though initial reported infections started a month later.

Figure 2 South Korea Cases, Daily Growth Rate and Curve-fits

The Italians are having tougher time.  Italy is the European country most severely impacted by COVID-19.  To promote tourism, Italy recently expanded air travel with China, and compared to other countries in Europe has the largest number of air connections with China.  Travel and other isolation restrictions within the country were only gradually imposed, which allowed the virus to spread.  Italy’s relatively old population also makes their citizens more vulnerable.  Once their reported data settled down in late February, their day-over-day growth rate is being reduced by only 5%.  Their number of cases is not near a plateau.

Figure 3 Italy Cases, Daily Growth Rate and Curve-fits

As Figure 4 shows, data for the USA is messy, and the current situation to date is not encouraging.  The data did not settle down until early March, and the day-over-day growth rate is nearly flat.  This probably reflects the fact that as more testing comes online, people who have been infected for a while are just now being counted.  The day-over-day reduction in growth is currently just 1.4%, and we are not nearing a plateau in the number of cases.

Figure 4 USA Cases, Daily Growth Rate and Curve-fits

Using the day-over-day growth reduction values for South Korea, China, Italy and the United States, Figure 5 shows what the case counts in the USA could look like by the end of April.  Now that federal, state and local governments, businesses and the public are taking action, the USA “Business as Usual” line is unlikely to occur.  We also have not acted as quickly as South Korea, nor do we have as much testing, so we are not likely to follow their line.  The more likely scenarios are somewhere between China and Italy, which means we would have 30,000 to 300,000 cases of Covid-19 by the end of April.  With a 1.8% probability of death if infected, the number of deaths from Covid-19 would be between 540 and 5,400.

Figure 5 End of April Projections of Covid-19 Cases in the United States

As of this writing on March 18th, there are 7,339 confirmed cases in the USA, and there have been 116 deaths due to COVID-19.  The situation will get worse before the worst is over, which may be a month away given China’s experience.  Even if these projections are off by a factor of 10, they are much much lower than the worst case and other estimates noted above.   To make this happen, it is critically important for the government to accelerate testing to establish situational awareness and get infected people treated as early as possible.  The public should avoid large groups and follow social distance and cleanliness guidelines.

References

www.nytimes.com/2020/03/13/us/coronavirus-deaths-estimate.html

www.nbcnews.com/health/health-news/live-blog/coronavirus-updates-live-u-s-cases-top-1-000-spread-n1155241/ncrd1155736#liveBlogHeader

www.ourworldindata.org/coronavirus

www.worldometers.info

www.pharmaceutical-technology.com/features/covid-19-italy-coronavirus-deaths-measures-airports-tourism/

www.pharmaceutical-technology.com/features/coronavirus-affected-countries-south-korea-covid-19-outbreak-measures-impact/