A few weeks ago I attended a very interesting online seminar, Economics in the Age of Covid-19, by University of Toronto professor Joshua Gans. Over the past 18 months, professor Gans has been conducting research and writing extensively on the impact of Covid-19, including a number of articles, a newsletter, and two books. His key thesis is that a pandemic is fundamentally an information problem. If you know that someone you interact with is potentially infectious, you can take actions to limit the interactions. However, if you have to guess whether a person is infectious, you’re taking a risk. Not only can you become infected, but you might also pass that infection on to others.
“The difference between perfect knowledge and no knowledge is what causes an infectious disease to have an impact on social and economic interactions,” wrote Gans in The Pandemics Information Gap, first published in April of 2020, followed by an expanded second edition in November of 2020. “With perfect knowledge, some people get sick, they are isolated, and life is (for most of us) essentially unchanged. … perfect knowledge allows you to avoid all infected people. No knowledge makes it near certain that you will encounter at least one infected person.” Furthermore, when we don’t know who is infected, we have to act as if everyone is infected, which then leads to major economic and social disruptions, including near-empty offices and city centers, decreased travel and leisure activities, and learning from home instead of in school.
In his seminar, Gans cited the 2002 SARS outbreak in China, Hong Kong, and Taiwan and the 2015 MERS outbreak in South Korea as examples of pandemics that were quickly contained. With SARS and MERS, people only became infectious when they developed a fever, cough, and other easily identifiable flu-like symptoms. Anyone suspected of being infected could thus be quickly isolated before infecting many others. This made it possible to contain the SARS and MERS viruses within a few short months, and to suppress them completely a few months later.
The 2020 COVID-19 outbreak was different. About a third of the people infected with the virus were asymptomatic carriers who didn’t develop noticeable symptoms but were still capable of infecting others. Of the people who showed symptoms, around 80% were only mild to moderate. And, there was generally a delay of several days between the time a person first became infected and the appearance of the first symptoms. In other words, the information problem was relatively straightforward with SARS and MERS, which made them easier to manage and contain, whereas managing the information problem with COVID-19 has been much, much harder.
Testing and contact tracing have been extensively used in an attempt to manage this COVID-19 information gap. Given their experience with the 2002 SARS outbreak, South Korea, Taiwan and Hong Kong quickly put in place extensive testing and contact tracing and were thus able to avoid the major lockdowns that the US and other countries were forced to implement.
As Gans explained in the seminar and in various articles, there are different kinds of COVID-19 tests. The key decision that should guide which test to use is whether one is looking for people who are infected, or for people who are infectious. “An intuitive notion that guides tests for the presence of a virus in an individual is that it is preferable to have tests that have the capability to detect smaller loads of the virus in any given sample (e.g., blood, saliva or nasal mucus),” he wrote in Test Sensitivity for Infection versus infectiousness for SARS-COV-s, - a September, 2020 NBER paper.
PCR tests were the most commonly used to detect the presence of the COVID-19 virus, especially in 2020. PCR can detect very small amounts of the virus. “Moreover, after the most infectious period in an individual, the PCR tests can still detect infections and, indeed, can detect viral remnants that may not be alive.” PCR tests are the gold standard if you want to know whether someone is infected with the virus. But they can be rather expensive, require specialized machines and a trained person to operate them, and are subject to lab processing delays from several hours to a few days.
“However, while being infected is a necessary condition for infectiousness, it is not sufficient,” added Gans. “With the Covid-19 pandemic of 2020, it has been discovered that individuals who are infected … may not be infectious. This is because infectiousness both requires an individual to have a sufficient viral load and the virus present has to be active. This implies that, if your relevant clinical decision is to isolate an individual to prevent infections in others, … the intuition that you prefer a more precise test falters and less precise tests can be more valuable.”
By contrast, antigens tests costs significantly less, - generally under $20; return results in as little as 5 minutes; and require minimal training or testing infrastructure. “Thus, even though the antigen test is less accurate for identifying an infection than PCR, its cost and consequently frequency of application that allows may make it a more effective tool for mitigating the spread of Covid-19.”
But Gans makes a stronger claim. “That even in the absence of a cost advantage or more frequent testing, a test with a higher limit of detection (e.g., an antigen test) may be more informative than a test with a lower limit of detection such as the ‘gold-standard’ PCR test. In particular, when a test’s efficacy is measured with respect to the decision being taken (isolation versus treatment), an antigen test can be more efficacious. In other words, it may not be ‘poorer’ but superior.” A recent NY Times guest essay, Rapid Tests Are the Answer to Living with Covid-19, made a similar argument.
In The Pandemics Information Solution, - published earlier this year and also available as a free PDF, - Gans turned his attention to the issues, trade-offs and potential solutions that should be used by key decision makers to help manage the pandemic and restore normality. These include:
Matching information to purpose. A test is a means of gathering the information needed to make better decisions. Thus, when developing a test, it’s important to clearly articulate the decisions we want the test to help us make. With Covid-19, tests provide information to help us improve four broad decisions:
- diagnosis - whether to treat or monitor a patient for complications;
- clearance - whether to allow an individual to interact with others in a close physical setting;
- mitigation - whether to isolate someone from other people; and
- surveillance - whether to engage in wider interventions to prevent the spread of disease.
Screening for Safety. “To solve the pandemic information problem, we need a test that will tell us whether someone is infectious and not simply infected with the coronavirus.” Rapid inexpensive tests enable us to systematically sort infectious and non-infectious people.
Sustainable systems. We need a system that that can function at scale for a long period of time. Such a system should be able to deliver and implement high volumes of tests at low costs, it should be easily accessible to people with minimal inconvenience, and should be accompanied by behavioral interventions to encourage people to follow its recommendations.
Surveillance Data. With population-level data it’s possible to get early warning of potential outbreaks even at a very local level. Such data can be collected from wastewater, for example, and analyzed using AI algorithms. Also, having more information about the networks of interactions among people would make it possible to have more targeted interventions to deal with outbreaks, thus reducing their economic impact.
Personal Risk Management. This requires providing people with information about the prevalence of disease within their own networks so they can adjust their behavior to mitigate their personal risks.
Contact Tracing. Forward tracing helps identify who might have been exposed to an infectious person, while backward tracing seeks to identify who gave the virus to an infected person.
“Viruses get out of control unless dealt with quickly,” wrote Gans in conclusion. “Gather the right information and we have an arsenal for attacking pandemics.” However the information needs to be used “to inform decisions, such as whether to isolate riskier individuals from others, or deciding which areas of the economy need to be locked down. … When decisions are made blindly, costs are large and actions take too long. By contrast, preemptive information acquisition enables those with the authority to stop pandemics.”
"In regard to Covid-19, multiple failures in obtaining information and then applying the right information to key decisions have led to our economic and social calamity. For potential Covid-29s, we need to do better. We need to take that core lesson and ensure that we have institutions with both the information and the authority to act.”
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