31 March Seasonality of COVID to be expected?

Tue, 03/31/2020 - 18:55

A colleague asked: What is the influence of ambient temperature on a virus like corona: will it disappear when it gets warmer? Can that explain few cases around the equator? Does it reappear in the fall or winter? Could climate change contribute to the emergence of more such viruses in the future, or for instance also moving tropical diseases more to the north, or other diseases just disappearing?

Well, the short answer for SARS-CoV-2 is: wait and see. But, in the meantime, what can we learn from the other human CoV?

  1. Two papers on the “seasonality” of the rather “benign” viruses HCoV 229E, HKU1, NL63, and OC43 in nasal swabs from symptomatic children ≤18 years, mainly causing respiratory problems in young children. The data from the US (J Pediatr Infect Dis 2018 shows the “textbook-like” winter and early spring predominance (Fig 2 p. 155). The paper in the Eur J Clim Microbiol from Ghanzou, subtropical area in China, shows a more variable pattern “…with the highest recorded prevalences were February 2011, April 2011, April 2012, August 2012, July 2013 and January 2014.” So clearly, it may occur in the summer as well. Nevertheless, from a review of several studies, these authors conclude: “seasonal patterns vary between countries and over time, it is apparent across all studies that the prevalence of HCoV among children is lowest in early summer”    
  1. With regard to the “old SARS”, there is an interesting paper of 2011, where it is shown that the epidemic started in Nov 2002 in China and ended in June 2003 everywhere (Table 1 p.2). The authors go on and try to explain this by an in vitro experiment (Fig 2 p. 3) showing that the virus remains infectious in either soluble or dried form for many days, at ambient temperature and relative low humidity, but in really “tropical conditions” (38 °C and 95 % humidity) decays much more quickly

So far, it looks all consistent, but then they show the meteorological conditions (in 2005!? -Table 2 p. 5) and I don’t see a lot of variation over time in the various places.  Puzzling.

In their discussion they make two remarks that put things again  into perspective:

  • In countries such as Singapore and Hong Kong where there is intensive use of air-conditioning, transmission largely occurred in well-air-conditioned environments such as hospitals or hotels.
  • Further, a separate study has shown that during the epidemic, the risk of increased daily incidence of SARS was 18.18-fold higher in days with a lower air temperature than

in days with a higher temperature in Hong Kong [24] and other regions [15–17 ).

So, clearly, for the “new” SARS-CoV-2, “the jury is still out”.  In view of the close similarity between both SARS viruses, you can presume or hope …..

As a “bonus”, I add a very nice overview on the pathogenesis of SARS and MERS…