Seasonality, Susceptibility, and Transmission of SARS-CoV-2

If you’re following the scholarship relating to the present pandemic at all closely, you should find this paper from Science very illuminating. Be aware that it’s pretty technical. In the paper they explore the effects of seasonality (the tendency of a virus to return on a seasonal basis) and susceptibility (which includes but is not limited to acquired immunity) on prevalence. Here’s a snippet from the conclusion:

In summary, the total incidence of COVID-19 illness over the next five years will depend critically upon whether or not it enters into regular circulation after the initial pandemic wave, which in turn depends primarily upon the duration of immunity that SARS-CoV-2 infection imparts. The intensity and timing of pandemic and post-pandemic outbreaks will depend on the time of year when widespread SARS-CoV-2 infection becomes established and, to a lesser degree, upon the magnitude of seasonal variation in transmissibility and the level of cross-immunity that exists between the betacoronaviruses. Social distancing strategies could reduce the extent to which SARS-CoV-2 infections strain health care systems. Highly-effective distancing could reduce SARS-CoV-2 incidence enough to make a strategy based on contact tracing and quarantine feasible, as in South Korea and Singapore. Less effective one-time distancing efforts may result in a prolonged single-peak epidemic, with the extent of strain on the healthcare system and the required duration of distancing depending on the effectiveness. Intermittent distancing may be required into 2022 unless critical care capacity is increased substantially or a treatment or vaccine becomes available. The authors are aware that prolonged distancing, even if intermittent, is likely to have profoundly negative economic, social, and educational consequences.

or, as others have put it more succinctly, we need to ensure that the cure is not worse than the disease.

There is an enormous number of things we simply don’t know. In the past I have suggested that the closest analogy we have to SARS-CoV-2 is the seasonal flu and that’s the assumption on which this paper is predicated but we just don’t know. The paper is silent, as it should be, on whether “highly-effective distancing) or contact tracing are practical in the United States. I incline towards believing that neither can be due to our physical and population size, the structure of our society, and our low degree of social cohesion.

I strongly believe that investigations of this sort should inform policy which is not to say that experts should be making the policies. Relying on science and putting policy decisions in the hands of scientists are not identical. Indeed, effective policy cannot be left to the experts.