Bad news came in over the weekend. Cases are up in Mumbai, and in several smaller towns. Kerala, which had beaten back the pandemic in its early days, has been going through enormous pains in recent weeks. This week, overall, cases are up in India by about a third. We seem to be at the beginning of a second wave. Friends around Mumbai have been discussing the inevitability of such a thing ever since the local trains were opened to the general public. I have been playing the devil’s advocate (what an appropriate phrase at this time) with the argument that if livelihoods are to be safeguarded, we have no choice but to let people move around. An increase of cases today inevitably leads to the conclusion that the policy changes made two or three weeks ago are at the root of the problem. Governments agree, and sometimes have gone the whole hog again, imposing full lockdowns in some towns.
My early training predisposes me to seek answers in an engineering discipline that is called Systems Design and Control Theory. One of the things that we learnt was that you could try to control a system by using its output to influence its input. This is called feedback. There is a theorem which says that feedback with delays leads to oscillations. Every teenager who has tried to form a rock band knows about the screech of feedback which badly placed mics and speakers can lead to. Others can more easily relate to the frustrating experience of making sure that the water in the shower is a comfortable temperature as an experience of oscillations due to delayed feedback.
Why should this lead to second and third waves of epidemics? The argument goes something like this. When it becomes clear that there is an epidemic, governments put various restrictions in place. But these are temporary, and when the number of cases decreases they are removed. Clearly there is a feedback. The delay comes from two sources: it takes time to realize that there is a consistent rise (or fall) in the number of cases, and it takes time for committees to make decisions.
Fortunately, the theorem assures us that we are not doomed to be tossed about forever by waves of the pandemic. If there is friction in the system then that damps out the successive waves. Where does this friction come from? One is the brutal calculus that the most susceptible are the earliest victims of the epidemic, so successive waves of disease, eventually, find better prepared immune systems. The second source is our personal learning and initiative. When we realize that there is danger, we personally take precautions. And we learn what are the most important, and best, measures. The third is the most enlightened reason of all: medical practice evolves, so that treatments and vaccines become available.
Human behaviour is unpredictable. There are no theorems which guarantee how I will act. Still, when studying a large enough body of people, there are general principles which seem to govern how such collections will respond to circumstances. There are limits to such predictions. Different countries, even different cities, have had a their second and third waves of COVID-19 at different times.
There are just three simple things to remember about COVID-19: mask up, keep your distance when possible, and do not gather with many others.