Complex Systems and Non-Linear Effects
Zynep Tufecki has an excellent analysis in the Atlantic of why Covid has been such a shock to every health system in the world. In short, we humans tend to be poor at systemic analysis, especially of complex systems with non-linear outcomes. This leads us to tend to under-estimate the impact of certain events – the result isn’t just a bit more, it can be suddenly and surprisingly catastrophic.
In many complex systems, efficiency, redundancy, and resiliency pull in different directions: More efficient systems, which are cheaper, eliminate redundancies, which provide resilience but cost more. For example, commercial airplanes always have two or more engines and have a co-pilot, even though one pilot and one engine is sufficient to fly the plane safely. The redundancy adds to expenses, but increases safety and resiliency in case something happens to one pilot or engine. In fact, commercial aviation is so safe because redundancy is mandated by regulation and built into every level, but our commercial-flying experience is so miserable because airlines have made it as efficient as possible to save money. (If one plane doesn’t arrive on time, there is no backup waiting to fly instead, for example.)
Health systems are prone to nonlinear dynamics exactly because hospitals are resource-limited entities that necessarily strive for efficiency. Hospitals in wealthy nations have some slack built in for surge capacity, but not that much. As a result, they can treat only so many people at once, and they have particular bottlenecks for their most expensive parts, such as ventilators and ICUs. The flu season may be tragic for its victims; however, an additional, unexpected viral illness in the same season isn’t merely twice as tragic as the flu, even if it has a similar R0 or CFR: It is potentially catastrophic.
Worse, COVID-19 wasn’t even just another flu-like illness. By January 29, it was clear that COVID-19 caused severe primary pneumonia in its victims, unlike the flu, which tends to leave patients susceptible to opportunistic, secondary pneumonia. That’s like the difference between a disease that drops you in the dangerous part of town late at night and one that does the mugging itself. COVID-19’s characteristics made it clear that the patients would need a lot of intensive, expensive resources, as severe pneumonia patients do: ICU beds, ventilators, negative-pressure rooms, critical-care nurses.
This is why the case-fatality rate for COVID-19 was never a sufficient indicator of its threat. If emergency rooms and ICUs are overloaded from COVID-19, we will see more deaths from everything else: from traffic accidents, heart attacks, infections, seasonal influenza, falls and traumas—basically anything that requires an emergency-room response to survive. If COVID-19 causes a shortage of masks for emergency-room workers, hospitals will stop everything that looks “elective” or nonurgent to fight that fire, but that means people will then suffer and die from things that those surgeries were intended to treat or improve. An angioplasty may not be urgent that week, but it is still a lifesaving intervention without which more people will die. This is true for even seemingly optional health interventions: If people can’t get knee-replacement surgeries, for example, they will be less active, which will increase their health risks.