Let’s talk about how the weather affects epidemics and about how, relatedly, there are waves of deaths across time during epidemics. It may seem early to think about this, but we are just at the beginning of the *first* wave of COVID-19, but likely not the last. 1/
Epidemics have always been with us. Here is a long and sad well-curated list: en.wikipedia.org/wiki/List_of_e…. Why epidemics *end* altogether is itself an interesting question (for another day). (Image: Plague panel with the triumph of death. 1607–35) 2/ 
We have survived flu epidemics before, though many people die. We will survive this one, though *very* many will be afflicted. And COVID-19 will likely become “endemic": now that it's here, it will remain with us. SARS-CoV-2 resembles viruses that cause common cold, in fact. 3/
However, at present, we are just facing our first wave of COVID-19. It may be premature to think of subsequent waves peaking, but there almost surely will be such waves. We must plan for the long haul. 4/
Peaks in epidemics have to do with: pathogen flows across networks; other social factors (like changes in population mixing across time, or major congregations, like wars or elections); and weather. For instance, flu has a baseline seasonality. cdc.gov/flu/weekly/wee… 5/
This seasonality of influenza has been known for a long time history.navy.mil/research/libra…. And newly emergent pandemics, like existing diseases, often obey such seasonality too. 6/
During the 1918 pandemic flu, there were *three* different waves of illness, starting in March 1918 through the summer of 1919. The pandemic actually reached its zenith in the US during the highly fatal second wave, in the fall of 1918. cdc.gov/flu/pandemic-r… 7/
How might weather play a role in COVID-19? Preliminary studies by Chinese scientists of transmission of SARS-CoV-2 (virus for COVID-19), exploiting geographic variation in weather conditions across China, suggests illness peaks with average temp of 40F. medrxiv.org/content/10.110… 8/
Another study from China suggests that changes in weather alone (i.e., increase of temperature and humidity as spring and summer months arrive in the Northern Hemisphere) will *not* necessarily lead to declines in COVID-19 case counts medrxiv.org/content/10.110… 9/
Here is the relationship, for instance, between absolute humidity and the SARS-CoV-2 (COVID-19) transmission rate across Chinese provinces. Except for very low humidity, there is not much variation. Via Wei Luo (and also @mandl @mlipsitch et al) medrxiv.org/content/10.110… 10/
Hence, work so far suggests that we cannot expect a ‘weather cure’ for COVID-19, where it just disappears. There will likely be waves of SARS-CoV-2. It will come back again as it moves from N to S hemispheres with the seasons. COVID-19 will likely be with us for a long while. 11/
Paper just *now* posted by @mlipsitch @ctedijanto @StephenKissler @yhgrad & Ed Goldstein has sophisticated model that suggests that recurrent wintertime outbreaks of SARS-CoV-2 will probably occur after the initial pandemic wave. medrxiv.org/content/10.110… 12/
Current data suggests that it is extremely unlikely that spread of SARS-CoV-2 would slow in USA or Europe due to temperature or humidity in the summer. New analyses based on diverse country data. papers.ssrn.com/sol3/papers.cf… by @qasim_bukhari 13/
Yes, indeed, such pandemics come in waves. We are in the middle of first wave. Wave in Oct/Nov could be worse. There is no exit from COVID19 pandemic but that it becomes endemic in our species, w >55% of people immune from natural exposure or vaccine. cnn.com/2020/04/30/hea… 14/
