Covid Catastrophe Part II: Understanding Exposure and Spread


Covid Catastrophe is a seven part series examining the history of the COVID-19 pandemic, its impact on Maine and what data policymakers used to lock down society and centrally-plan our economy. Check back tomorrow for Part III.

Very little was known about this new virus in early 2020, as the world tried to secure accurate data from the opaque and corrupt Chinese Communist Party. Despite limits on credible information, science had determined a few crucial elements, which were informed by the surveys of passengers on quarantined cruise ships like the Diamond Princess.

We began to see that a surprisingly large portion of those exposed do not contract the new virus, and a substantial number of those infected do not experience symptoms serious enough to seek care. We learned that the elderly and those with preexisting conditions or a compromised immune system were at the highest risk.

A review of epidemiological studies from around the world shows a broad estimate of the range of asymptomatic COVID-19 cases. It is important to note that since many studies were not conducted across a broad range of time, they may have left out the accounts of subjects who eventually experienced symptoms outside the scope of a particular study. This variability is reflected in the breadth of the studies’ 95% confidence interval. Framing our understanding of the new virus in this way helps to put the official timeline in perspective.

A World Health Organization (WHO) review of four related studies from Brunei, China, Taiwan, and South Korea found that “between 0% and 2.2% of people with asymptomatic infection infected anyone else, compared to 0.8%-15.4% of people with symptoms.” It is generally understood that transmission from people who are not showing symptoms is rare. Whether those individuals are experiencing a truly asymptomatic case or some period before they exhibit symptoms, has been very difficult to study. 

A report from China, published in a July 9 WHO brief which noted it as ascribing “clearly and appropriately defined asymptomatic infections,” showed that 23% of those infected never showed symptoms. 

A study of the travelers on the Diamond Princess cruise ship, which was quarantined off the coast of Yokohama, Japan between February 5 and 20, showed that only 19% of the more than 3,700 guests and crew aboard became infected. Of those infected, over 50% showed no symptoms. Three-quarters of the infected were over the age of 60. A second study published on March 9 comparing the cruise ship data to that from mainland China, estimated the case fatality rate (CFR) at 1.1%. Of course, it should be noted that the 95% confidence interval spans a wide degree, between 0.3 and 2.4%. 

The Diamond Princess example presents an interesting case study, since the closed, contained nature of a cruise ship can simulate the population density of a city. Also, a ship on open water with a diverse array of individuals from Asia and North America helps to smooth out the potential geographic and cultural differences that in-country studies might present.

Although we cannot be sure of the true infection and fatality rates of this new disease, these case studies provide a ballpark within which to determine potential risk to the population. They show us that there are a substantial number of people who, although exposed to the virus, did not become infected, and of those, a substantial number did not experience symptoms indicative of serious illness. 

This information was available relatively early on; these studies were published in early March. If U.S. policymakers had heeded these early analyses, they may have held off on recommending wholesale lockdowns in the name of protecting a small segment of the population who would be truly in danger. They may have focused their limited resources on protecting vulnerable populations first, instead of trying to plan all of society.

Today, data from the Johns Hopkins University of Medicine Coronavirus Resource Center show the overall case fatality rate to be under 0.4%. The “best estimate” from the U.S. Centers for Disease Control and Prevention (CDC) peg the rate of asymptomatic cases at 35%.