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Countering Covid-19

The prognosis is grim. Millions dead, overrun hospitals, and insufficient ICU beds for the seriously ill. These are the outcomes absent mitigation strategies to slow the spread of the virus until the development of an antiviral drug for treatment or a vaccine. Unfortunately, both the solutions may take a year to 18 months. Barring their expedient development, the most probable outcome is that mitigation strategies will remain in force for upwards of six months. The business world shudders at the thought of closures for a month, let alone six months to a year. The conflict for the West is the balancing of individual liberty versus the common good when implementing mitigation strategies. The calamity is that this struggle will prolong the duration, magnify the economic impact, and place more people at risk. The hope is for the common good to prevail over the tragedy of the commons and bear this sacrifice at the altar of freedom.

Note: The disease spread model used in this analysis is available in an interactive dashboard.

Photo by CDC on Unsplash

Photo by CDC on Unsplash

Modeling Contagion is the domain of the epidemiologist. While the rest of the world wonders when this pandemic will end, scientists the world over create models to understand the path of the virus and others work to develop antivirals and vaccines. Recent projections for the US and UK are grim from the Covid-19 Response team at the Imperial College London. Millions dead in the US without effective mitigation methods to contain the spread of the disease. How did they come up with their projection? Robust mathematics based on hard data.

A standard model for disease spread is the Susceptible-Infected-Recovered (SIR) model. The critical dimension of a disease spread model is the reproductive rate (R0), which indicates how many people are infected by each infected person. Current estimates suggest a number of around two with a range between 1.5 and 3. This number derives indirectly from two other variables: the infection and recovery periods. The longer a person is infected, the more opportunity they have to spread the virus. Similarly, the longer a person takes to recover, the longer they can spread the disease. The trouble is that reducing the reproductive rate (or conversely, extending the time it takes to transmit the disease) requires knowing who has the disease.

Testing is Everything. There is an urgent need for testing people for the virus to ensure case isolation occurs, and the transmission time lengthens. Testing is partially the reason why South Korea is an outlier in fatality rates. Sick individuals can have severe symptoms, while most cases are mild to the point where a person might not even know they have the virus. Unfortunately, they can still transmit the virus to other people. Testing helps reduce this threat.

Testing permits health organizations to trace where an infected person acquired the virus. They can then treat the infected person to help manage the infection before it becomes critical. While there is currently no cure or vaccine, it is the virus interaction with other manageable health ailments that makes it deadly. Most importantly, they can use containment strategies to reduce the ability of the disease to spread. First, you isolate the infected individual to ensure that they don't pass it to anyone else. If they have not, their reproductive rate drops to zero. If not, the battle is to find whom they infected before they infect anyone and reduce their reproductive rate.

Exhibit 1. US Base Case Scenario of People Infected

Source: CRM calculations based on the SIR disease spread model with no mitigation methods. Click the graph to link to more details on the model.