Covid-19 and the hope for warmer weather

Yesterday our vast network of spies sent us an interesting analytical report from JP Morgan. Sadly, we cannot link it since it came by email. Strictly in the interests of the public health, however, we share this interesting fair use excerpt relating to the prospects for relief from the novel coronavirus as the northern hemisphere warms up:

Update: tracking COVID-19 outbreaks and geographical vulnerability bands (March 12, 2020)
This is controversial and many scientists are still uncertain about it, but there has been some research on COVID-19 outbreaks as a function of latitude, temperature and humidity. A paper just released from the Institute of Human Virology at the University of Maryland [(link to pdf)] which makes the following observations:
• The most severe community outbreaks have occurred in regions along a narrow east-west distribution roughly along the 30-50 N” corridor at consistently similar weather patterns (5-11°C and 47-79% humidity). Cities at greatest risk below are on the border of the yellow zone and the green zone
• Average temperatures (5-11°C) and relative humidity (47-79%) in affected cities are similar to each other, and also similar to laboratory conditions conducive to coronavirus survival (4°C and 20-80% relative humidity). None of the infection concentrations have occurred (yet) in places with minimum temperatures below 0°C either.
• Outbreaks have been lower (so far) in places with large populations and substantial travel connections with China, such as Bangkok

Which cities are most at risk? The table below show cities with community spreading and those deemed at risk by the authors of the study using their (in my view highly simplified) approach, simply due to the latitude and average temperatures/humidity of each. The authors note that the cities below will experience rising temperatures and humidity in the weeks ahead, and if temperature and humidity do affect the transmission of the COVID-19 virus, the passage of time could help. As the “ideal temperature/humidity” zone for the survival of the virus moves further north over time, the authors believe it would overlap with population centers with much lower density.

However, let’s be cautious here. The authors cite the decline in Wuhan infections as possibly being related to warming weather when there are many other factors involved: the rising effectiveness/severity of the quarantine, increased knowledge of the virus and social distancing by citizens, and “herd immunity” once a large percentage of the population has already been exposed to the virus. This paper makes an important contribution to virus severity tracking and suggests that weather may play a role, but the results are far from conclusive this early in the outbreak (for example, the only cities circled on the map are ones with >6 deaths as of March 5; there are a lot more cities that would have circles today, and I do not have an updated map overlaying these circles on latitudes/temperature zones). To me, the primary value of the paper is to highlight cities with potentially high risk, and secondarily, that we wait and see if weather may mitigate it. I would NOT recommend any reduction of density reduction and social distancing simply out of the view that weather will solve the problem. [Bold emphasis added.]

The same report, which is regularly updated, had an earlier bit that suggested the mechanism.

Update: Could the onset of spring and summer slow virus transmission rates? (March 4, 2020)
There have been press articles and government statements on the possibility that COVID-19 infection rates could fall as the winter comes to an end. There are three main theories as to why the flu season in temperate regions peaks in winter months:
• More clustering of infected and uninfected people indoors due to colder temperatures
• Colder, drier air is more conducive to airborne travel of viruses; colder air allows viruses to survive for longer periods and to travel longer physical distances
• Lower levels of winter sunlight may play a role given the ability of UV light to sterilize surfaces and kill both viruses and bacteria
Some details:
• Scientists have found that influenza peaks in periods of low humidity, low temperatures, low solar radiation and low precipitation. In other words: in cold, dry winter months
• In lab studies using animals, scientists also found that high temperatures and high humidity slowed the spread of influenza sharply, and at very high humidity levels, the virus stopped spreading completely
• During the SARS epidemic in 2003, infection rates declined from March to May as temperatures rose. However, there were other factors changing at the same time (changes in hospitalization rates, greater provision of gear to medical personnel, higher quarantine rates and the natural erosion of epidemic severity over time) so results were not conclusive with respect to weather in isolation. Even when combining all these factors, researchers were only able to explain two thirds of the change in SARS infection rates
• Why might infection rates be impacted by temperature?
o Low winter humidity might impair the function of mucus, which traps and expels foreign bodies like viruses or bacteria. Cold, dry air can render mucus drier and less efficient at trapping a virus
o In addition, influenza “virions” (an infective virus outside a host cell) appear to be much less stable in conditions of higher humidity, when respiratory droplets fall to the ground more quickly
• It’s not just the heat, it could be the sun as well. Direct and scattered radiation from the sun can break down viruses that have been transmitted to surfaces (“fomites”), but is much less abundant in winter. UV light is so effective at killing bacteria and viruses that it’s used in hospitals to sterilize rooms and equipment
o One study found that in Brazil, there’s a correlation between increased influenza hospital admissions and solar UV-blocking by smoke during the burning season
o The US military reported that UV radiation sterilization virtually prevented the spread of influenza among patients in a veterans hospital, during the same time that an epidemic of influenza ravaged similar patients in nearby non-irradiated rooms
• However, COVID-19 is not the same as influenza and SARS, and its reaction to changes in temperatures, humidity and sunlight is still unclear. SARS did not completely subside until late May 2003, which suggests that temperature factors, if they did mitigate the disease, took time to work
• If weather DOES play a role in COVID-19, then infection rates could FALL in the Northern Hemisphere as temperatures rise, but RISE in parts the Southern Hemisphere in June/July/August when temperatures fall there (i.e., what happens with the flu each year)

Read the underlying paper here.