In a recent note to clients, a team of researchers at Goldman Sachs took a close look at temperatures and studied whether there was a correlation with temperatures. Perhaps unsurprisingly, the team found a strong negative correlation between confirmed cases and temperature, with the number of the former going up while the number for the latter goes down.
As the regression modeled by Goldman shows, the further temperatures drop with a modest lag between the summer and the winter, the more extreme the surge in COVID-19 cases. This applies in both the US and Europe.
Using fixed effects modeling, the Goldman team then tried to strip out other factors to try and isolate and expose the influence of temperature on case growth.
Interestingly enough, the analysts analysis found that no matter the difference in statewide policies and enforcement, cases appeared to wax and wane along with changes in temperature, appearing to resist most efforts to control the virus.
This notion isn't all that surprising. Most other coronaviruses (ie the common cold), along with various influenza strains, are heavily influenced by temperature and seasonal effects (hence "flu season".
Medical literature cited by Goldman explains the seasonality trend in two key ways: Increase indoor social activity for "hosts", which increases exposure, along with the cold weather's impact on the immune system and general health (making individuals more vulnerable).
Armed with these models, Goldman's team of analysts produced a set of projections showing that the economies of the US and Europe will likely slow significantly during Q1 and Q4, followed by a springtime thaw as new case numbers start to recede.