COVID19 Measuring What Matters

The spread of COVID-19 through continents and communities is a recent example of the humanitarian challenge that accompanies globalization. From supporting the victims and their families, to supporting workers affected by decreased demand for products and services to developing a vaccine as well as new supply chains, there is much work to be done to respond and recover.

Health professionals are putting their lives at risk while experts in finance and economics are trying to determine how best to determine the implications to the economy.   

This article, however, has a much narrower goal. The objective is to determine what we know and what we do not know from the most relevant pieces of published data and metrics on the coronavirus outbreak. The hope is that armed with a better understanding of the data and its limitations, we are better equipped to tackle the larger societal challenges. 

The Outbreak 

Ten weeks ago, Chinese authorities identified a cluster of similar cases of pneumonia in the city of Wuhan in China. Wuhan is a city of 11 million inhabitants and capital of the Hubei Province.

These cases were soon determined to be caused by a novel coronavirus, now known as SARS-COV-2, causing COVID-19 disease. Coronaviruses are a group of viruses that are common in humans and are responsible for up to 30% of common colds (here).

Two outbreaks of new diseases in recent history were also caused by coronaviruses – SARS in 2003 that resulted in approximately 1000 deaths and MERS in 2012 that resulted in 862 deaths, according to the WHO (here).

Transmissibility

The data that will give us insight into the transmissibility of the virus is the reproduction number and the doubling time.

The Reproduction Number

The US Centers for Disease Control and Prevention estimates that the virus’s reproduction number (the number of additional cases that likely result from an initial case) is between 1.6 and 2.4 as compared to the seasonal flu (whose reproduction number is estimated at 1.2 to 1.4). 

What we know: This reproduction number range indicates that the virus causing COVID-19 is easily transmitted from person to person.

Even though transmission is high, there is increasing evidence that the growth is localized, partly because individuals, firms, and governments are taking strong countermeasures (including school closings and cancellation of public events).

For most geographies, transmission scenarios by health professionals assume a major epicenter for a majority of all cases, two or three smaller centers with 10 to 15 percent of all cases, and a “long tail” of towns with a handful or a few dozen cases.

What we don’t know: The evidence remains mixed about whether asymptomatic people can transmit the virus and the length of the incubation period.

For example, on February 4th, 10 people on board The Diamond Princess cruise ship tested positive for the coronavirus. It was the beginning of a nearly month-long ordeal and quarantine response. By March 1, it was reported that 705 people from the ship had contracted the virus.  

It was reported that more than half of the infected people did not exhibit significant symptoms (even though many passengers were middle-aged or older). But it remains unclear whether official statistics are capturing 50 percent or 20 percent of cases.  

As of March 6, the total number of confirmed cases on the cruise ship reached 696 patients, including 552 passengers and 144 crews. The number of conducted tests and patients declined because the source changed the way of calculation.

The Doubling Time

In an outbreak of an infectious disease the number of cases as well as the rate at which the number of cases is changing is important. A helpful metric to measure the rate of change is the doubling time.

The Doubling Time is the time it takes for the number of cases to double. For example, if the number of cases is 100 today and it was 50 three days ago then the doubling time is 3 days. The doubling time in a disease outbreak is not constant and will continue to change with time.

Since not everyone is tested, the doubling time only tells us the number of known cases (confirmed cases + suspected cases) not the total number of those infected.

What we Know: Based on the global WHO-data up to and including 9th March 2020, the doubling time for the global number of known cases: (including China) is 19 days and (excluding China) is 5 days.

The doubling time in China is longer because the number of daily cases has declined after the lockdown in China.

What we don’t know: The coronavirus disease has only mild symptoms for most people, so the number of confirmed and suspected cases is likely to be smaller than the number of total infected cases. At this time, what we still do not know is the doubling time of total infected cases. 

 The Case Fatality Ratio

The Case Fatality Ratio (CFR) is the % of deaths among confirmed cases. This ratio is dependent upon the identification of cases early in the disease, the intensification of viral-control methods, and the deployment of treatments.

Epidemiologists Zunyou Wu and Jennifer McGoogan analyzed a report from China Centers for Disease Control and Prevention that looked at more than 72,000 cases and concluded that the fatality rate for patients 80 and older was seven times the average, and three to four times the average for patients in their 70s. Other reports describe fatality rates for people under 40 to be 0.2 percent.

What we still don’t know: The outcome (recovery or death) of cases is still unknown. By calculating the number of people who have died from the coronavirus today based off of the number of people diagnosed with the virus, we will be aggregating people at different stages in the development of the disease. The time from symptom offset to death has ranged from 2 to 8 weeks. This means that there are many who are sick and will die, but have not died yet; leading to under reporting of the CFR. 

During the SARS-CoV outbreak in 2003, the CFR was initially reported to be 3-5%, but rose to 10% by the end. The low numbers that were published initially resulted in an underestimation of the severity of the outbreak. And the rise of the CFR over time gave the wrong impression that SARS was becoming more deadly over time.

What we know: According to the data published by the World Health Organization in their Daily Situation Reports, the virus disproportionately affects older people and those with pre-existing medical conditions (such as cardiovascular disease, chronic respiratory disease or diabetes) (here).

The CFR varies by location and is typically changing over time. But it can still provide insight as long as we understand its limitations. 

In the period up to and including March 9th 2020, the global Case Fatality Rate for COVID -19 is:

Globally = 3.48%. China = 3.96%. Rest of World = 2.39%.

A CFR might rise or be higher than another location because the outcome of more cases is known not necessarily because the virus is more severe in that location.

The case fatality rates for SARS-CoV and MERS-CoV were high: 10% and 34%, respectively. The US seasonal flu has a case fatality rate of approximately 0.1%, much lower than the current CFR for COVID-19 (here).

If we are going to be serious about dealing with the challenges of globalization, we must also be serious about measuring and understanding what matters.