Recently, Anthony Brookes, a Professor of Genomics and Health Data Science at the University of Leicester, wrote a piece for the Daily Sceptic arguing that central to the virus’s surge-and-decline behaviour is the emergence of new variants, which are “able to infect (or re-infect) some fraction of individuals”.
A series of SARS-CoV-2 variants have arisen, many of which possessed a transient selective advantage that led to a wave of infection that peaked some three-to-four months later. Several such variants have spread globally, though different successful variants have arisen simultaneously in a number of countries. The result is a three-to-four month wave pattern per country, which is also apparent globally.
The global wave pattern is shown below. It features an extended autumn and winter wave, a spring wave and a summer wave (seasons here for the northern hemisphere, of course). Note that this graph is raw positive test numbers so does not allow for increased testing.
To illustrate how this global pattern is reflected in different countries and how it relates to the emergence of new variants, I have superimposed the graph of variant proportions over time from the CoVariants website onto the positivity rate curves (the proportion of tests that come back positive, which takes into account changes in the amount of testing) from Our World in Data. I’ve done this for the 12 countries which have done the most sequencing of virus samples (according to CoVariants), plus Israel and South Africa.