Lower minimum temperature increases Covid-19 deaths with the interval of 15.9 days, statistics show
The second wave of Covid-19 has just started in Europe and the US is reportedly headed for the third wave. Looking back on the summer, Covid-19 was relatively tamed in the Northern Hemisphere. Florida and Texas were highly anticipated to follow the trail of NY, but despite the persistent inconsiderate behaviors, the death toll per capita didn’t become as bad as NY or New Jersey. On the other hand, the epicenter of infection was in South America. Interestingly in India, which has the second largest Covid-19 cases after the US, the death toll per capita is significantly low. What made this difference ?
In the beginning of the pandemic, Covid-19 was widely thought to be similar to the seasonal flu. Dr. Fauci and other experts expected it to dramatically slow down in summer. The cases continued to grow through summer actually, but there might be a hint to explain the difference above. The seasonal flu comes back every winter, so the weather statistics are crucial to resolve this puzzle. The detailed weather data is a necessary tool for insurance companies so I used their dataset this time.
The big data of weather statistics was obtained from visualcrossing.com. By matching the data to Covid-19 information from the University of Oxford, we might get an insight. However realistically, it’s not likely that today’s weather affects today’s Covid-19 cases or deaths. I thus shifted the weather data from 1 day to 90 days later so we see how present weather affects Covid-19 in the future. This time, I focused on Europe, which is in the middle of the second wave now.
As a result of the analysis, the significant opposite correlation was confirmed between the minimum temperature and Covid-19 deaths in 20 out of 32 countries, where the data is available. At average, the minimum temperature affects Covid-19 deaths with an interval of 15.9 days. Let’s look at the list of the countries, intervals, and the correlation coefficient. It’s from 0 to -1, and the correlation is stronger when it’s close to -1.
Austria 11 days -0.58
Belgium 16 days -0.62
Denmark 15 days -0.70
Estonia 17 days -0.53
France 16 days -0.41
Germany 24 days -0.67
Italy 13 days -0.67
Ireland 27 days -0.40
Lithuania 17 days -0.35
Netherlands 18 days -0.60
Norway 12 days -0.47
Portugal 23 days -0.63
Spain 5 days -0.49
Slovenia 5 days -0.48
Sweden 33 days -0.74
Switzerland 15 days -0.61
UK 18 days -0.55
Finland 22 days -0.46
Luxembourg 7 days -0.48
Slovakia 4 days -0.35
Actually in most of the western countries, the significant opposite correlation was confirmed. Sweden, where it did not experience lockdown, has the correlation coefficient of -0.74. This is a very strong opposite correlation. -0.67 in Germany and Italy, and -0.62 in Belgium are also strong enough to conclude the minimum temperature affects Covid-19 deaths with about 2~3 weeks intervals. It means about 2~3 weeks after the minimum temperature drops, more people die from Covid-19.
Some of the readers might say that old people are sensitive to the cold weather even without Covid-19. This is true. Generally being exposed to the cold air can cause heart attack or worsen chronic disease. This might have triggered deaths among the old Covid-19 patients. However I actually analyzed the data from when a country recorded the first death, when it was around the end of February and March, until 20th October 2020. The data includes the whole summer, and also the warm countries such as Spain, Italy, and Portugal. More importantly, the opposite correlation is seen only with the minimum temperature, not the average temperature of the day. The virus took advantage of the coldest moment of a day.
What should we think about this ? The maximum temperature and the average temperature don’t affect Covid-19 deaths. This implies that the high temperature doesn’t deactivate the virus. Instead, the virus takes advantage when it’s cold. This explains why the infection didn’t stop in summer but only slowed down. Virus doesn’t breed outside human bodies. Increasing when it’s cold means probably it is happening in the end of our respiratory organs that are exposed to the outer air, such as the nose or throat. We know our noses feel cold in the winter morning. It is implied that Covid-19 is relatively tamed in Asian countries. Though there are some exceptions, if that is true, maybe this is related to the shape of the nose. I am Japanese and I know Asian people don’t have pointed noses. Compared to other races, our noses are closer to the main part of the face. It is thought to be obtained through the harsh winter in Mongolia. Unfortunately I could not find the thermo data of noses across the races, but if the temperature of nose affects Covid-19 deaths, wearing a face mask should be also protective.
