Reading the latest news, everybody has to be concerned about the Coronavirus and its impact on daily life of billions of people. The Coronavirus (virus is officially labeled as SARS-CoV-2 and its disease as COVID-19) is spreading quickly around the world, causing unprecedented lockdowns of huge regions and cities, havoc on markets and overload of health facilities in affected areas.
Some countries seem to have already contained the major spread of virus (China, South Korea), some are currently experiencing the initial extreme increase of patients with severe cases (Italy, Iran), with the rest of the world expecting it in upcoming weeks and trying to prepare for it.
Question is, will the rate of spread slow down or even disappear at all? It definitely will.
Check this nice video demonstrating the principle of exponential growth and epidemics
It’s essential to understand that even a very small decrease in “probability of exposure becoming an infection” (referred as p in the video) can reduce the growth of the spread significantly or even stop it completely.
But why do we discuss it at Windy.com, we normally talk just weather, right?
The reason is the outside temperature. Spread of typical flu highly correlates with weather, having its season peak in cold months, declining during spring with almost no cases during the warmest part of the year. Recent studies show that high temperatures and especially high humidity slows the influenza spread. More moisture in warmer air behaves as a barrier for airborne viruses so droplets of cough or sneeze cannot travel as far as they would in colder, dry air.
Of course, more factors can play a role in this flu seasonality (longer sunlight exposure, less clustering of people indoors), but temperature is considered as the major one.
There is a whole family of coronaviruses, some of them already known to humans, causing mild colds and behaving similar to the flu - in warmer climate, they tend to decline. That is the reason why many people believe that same will happen with COVID-19. As stated above, even the slight decrease in person to person transfer rate of the virus has a huge impact on overall number of cases. Will a higher temperature and humidity help us in this way? There are many opinions on that subject, but most experts agree, that it’s too early to judge and only hard data from summer season and their detailed analysis will tell us the truth.
But until then, we have no other option than to make assumptions based on data we have now.
Posts discussing weather patterns (temperature/humidity):
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As mentioned, the COVID-19 is not all that unknown to us, we had coronavirus strain SARS back in 2003. SARS had its peak in winter months and faded away during May. Typically influenza season falls sometimes between the beginning of fall and the end of spring. So the SARS did not really exceed the usual influenza season trend. But can we expect COVID-19 to follow this path as well?
The current spreading rate tells us a fact, that the COVID-19 has more incidences in places with dryer and colder environment than in more humid and warm locations. For instance let´s take a look at Japan, we would expect the virus to be spreading mainly in big cities like Tokyo, due to a number of foreign visitors and population. But this is not the case, COVID-19 is actually spreading in Hokkaido, despite it has a much lower frequency of travellers. However the weather conditions there are favorable, dry and less humid environment. The same goes for Italy and its epicenter Milan. North of the country is significantly more affected than the south.
On the other hand, it would not be wise to expect the novel coronavirus to behave as the ones before.
It is necessary to say, that SARS 2003 did not go away just because weather got warmer. It was followed by national interventions to isolate cases and everyone, who had the possibility to be infected.
We have already said that the environment plays a key role in influenza activity and dry/cold weather with low humidity favors the transmission. But influenza epidemics often appears in a tropical and subtropical regions during rainy seasons with obviously high humidity values. In other words, there are two types of influenza environments. In cold-dry environment, where humidity/temperature goes below 11–12 g/kg and 18–21°C, influenza peaks during cold months. In humid-rainy case, if humidity/temperature does not go under those values, influenza peaks during rainy season.
Immunity is another factor, which is worth a consideration. Our immunity is significantly worse in winter than in summer and we also lack vitamin D, because of less ultraviolet light exposure in cold months. Vitamin D benefits our immune system and helps us to be durable against numerous diseases, even so this factor can be observed as not so important in relation to influenza activity.
But then again, new viruses are likely to persist longer than a common ones, which have been in the population for years or decades.
We at Windy.com are no experts in the area of viruses, but we have access to the best weather data available.
We have assembled temperature records for each country (taken from the area of major spread of the virus within the country or the capital of that country) and pictured them along with recent Coronavirus spread data (daily amount of new cases, sourced from Coronavirus COVID-19 Global Cases by Johns Hopkins CSSE) to see if there could be any correlation.
Based on the charts above, we can see a slight correlation in relation with a higher temperature and virus decrease, and opposite a lower temperature and faster spread of COVID-19.
Of course, there are many drawbacks in this approach:
data coming from different countries aren’t easily comparable (some countries test much more than the others, some have much highly populated areas, also quality of data coming from some countries is more than questionable)
the virus has quite a long incubation period, therefore “new” cases are being reported several days after the people were actually infected (but at least average temperature at given location can help to mitigate this effect)
there are still not that many daily observations, the data window is quite too small
correlation does not imply causation” - even if there seems to be a visual dependency between the temperature and the increase/decrease rate of new cases, it is absolutely no proof that there is a correlation between those two
As always there are many opinions and very little data to predict anything for sure. So the truth will be somewhere in the middle. It should be essential to avoid any catastrophic predictions as well as not to underestimate it.
The latest data for China shows a retreat of Coronavirus cases and high amount of recovered patients in a comparison to the total amount. Other countries will hopefully have the same progress.
Not happy with the findings? Don’t despair. If the weather won’t help us, there are still many ways, how each of us can help - avoid crowded places, work remotely if possible, stay fit, wash your hands, do not touch your face.
Avoid face to face social contacts for a while - read a couple of books or go online! There is still a lot to explore, also at Windy.com.