The Centre for Evidence-Based Medicine at Oxford University is offering a glimmer of hope that summer could bring a respite from SARS-CoV-2.
Alaskans looking at a commercial fishing season disrupted by the pandemic coronavirus and a tourist season likely destroyed by it could hardly ask for more as April quicky heads into the May that is the start of the glorious season of the midnight sun.
“The relationship to seasonality and evidence of an association with weather conditions, the concentration of COVID’s impact in a small number of countries and the association with latitude provides evidence that environmental factors impact on the transmission of SARs-CoV-2,” the Centre concluded Monday after a rapid review.
The thinking is that “cold and dry conditions” boost the spread of the disease with warm, humid and sunny conditions doing the opposite.
As is regularity noted in studies of this type, however, correlation is not causation even if there are indications the virus is slowed by sunlight and warmth.
A Spanish scientist and a Finnish colleague in March also noted that “most outbreaks display a pattern of clustering in relatively cool and dry areas. The predecessor SARS-CoV-1 was linked to similar climate conditions. Should the spread of SARS-CoV-2 continue to follow current trends, asynchronous seasonal global outbreaks could be expected.”
Miguel B. Araújo from the National Museum of Natural Sciences in Madrid and Babak Naimi from Helsinki University forecast that the spread of SARS-CoV-2 would be limited by the “ecological constraints” that limit all organisms.
“Building on the concept of ecological niche, we develop projections of monthly
changes in the climate suitability for SARS-CoV-2 outbreaks. Projections are
obtained from an ensemble of 10 familiar machine learning ecological niche
models(, each with 20 replications generated by repeating four times a five-fold
cross-validation that accounts for and enables the quantification of variability
across initial conditions,” they wrote in a paper posted at medRxiv pending peer review.
Check the weather
They found the now-deadly coronavirus survives best in areas with a temperature range of 26 to 55 degrees and sunlight radiation values of 61.07 to 170.96 watts per square meter (W/m²). The sweet spot for the virus is, by their calculations, 42.5 degrees and 112.78 W/m².
A study on the “Solar Radiation Climatology of Alaska” would put the Anchorage Metro area near 112.78 W/m² in March. The average March temperature for the area is 26.6 degrees, according to the National Weather Service.
These are not quite ideal conditions for SARS-CoV-2 as calculated by Araújo and Naimi. The sunlight level is near the peak, but the temperature is a little cold.
Conditions would appear to be improving into April, however, with the average monthly temperature rising to 36.8 degrees – just below the 42.5 mean for optimum SARS-CoV-2 survival – and with radiation level remaining below 150 W/m², which is above the calculated optimum level for this virus, but within the range.
By May, however, with that midnight sun on the rise, the solar radiation in the Anchorage area – as well as across most of the state – is up to or over 200 W/m² and the average monthly temperature has hit 47.8.
That temperature is still within the comfort zone for SARS-CoV-2, but by June the average temperature is up to 55.2 – above the coronaviruses zone – with the solar radiation above 200 W/m².
Could this mean that the SARS-CoV-2 burns out in the 49th state summer?
Nobody can know for sure because SARS-CoV-2 is a newly evolved pathogen. It has no track record.
As Araújo and Naimi duly note, climate can exert powerful influences on “virus-transmitted diseases. (But) of course, not all viruses are climate determined. HIV/AIDS, for example, is not affected by external climatic factors. The virus is transmitted by sexual intercourse, blood transfusions, or from mother to child during pregnancy, delivery or breastfeeding, so it never leaves the host’s internal environmental conditions.”
Most scientists expect this SARS-CoV-2 to behave more like the original SARS – now known as SARS-CoV-2 – than HIV. SARS-CoV-2, Araújo and Naimi wrote, “involves aerial transmissions of respiratory droplets or fomites, exposing the virus to external environmental conditions in which transmissions take place.
“Our models fitted on the existing pattern of spread (of SARS-CoV-2) between January and March 2020, support the view that incidence of the virus could follow a seasonal climate pattern with outbreaks generally being favored by cool and dry weather, while being slowed down by extreme conditions of both cold and heat as well as moist.
“Prevalence of respiratory disease outbreaks, such as influenza, during wintering conditions is common. But the similarity of climate determination of SARS-CoV-2 with
its predecessor SARS-CoV-1 and even MERS-CoV is noteworthy, raising
reasonable expectations that fundamental traits shared by at least these three
coronavirus might be conserved.”
The climate-related predictions of Araújo and Naimi as to when the disease might blow up do appear to track well with conditions in the Seattle area, site of the first big U.S. outbreak, and those in the New York and Boston areas, the sites of later huge outbreaks.
The Centre’s “rapid review” offered this observation:
“The lack of viral activity in countries with high temperature and high relative humidity might explain why they do not have major community outbreaks of SARS, and why they have found it easier to manage the SARs-CoV-2 outbreak.”
Hong Kong researchers concluded “low temperature and low humidity environment(s) may facilitate its transmission…in subtropical areas (such as Hong Kong) during the spring and in air-conditioned environments. It may also explain why some Asian countries in tropical areas (such as Malaysia, Indonesia or Thailand) with high temperature and high relative humidity environments did not have major community outbreaks of SARS.”
There are reasons to hope Alaska’s friendlier season could bring some relief from the threat of pandemic disease, but the outliers caution against getting too carried away.
Generally warm and sunny Spain has now endured one of the most-extreme lockdowns in Europe only to see its death rate climb to 510 per million – about three times the current death rate in the U.S. and more than double the death rate in Sweden, which has stirred some controversy in Europe, and journalistic criticism in this country, for refusing to order people to isolate in their homes.