The chilly climate may increase the chance of infecting COVID-19.

Dear editor,

Up to February 2021, the outbreak of COVID-19 caused more than 100 million infections and 2 million deaths (WHO, Coronavirus disease 2019 Situation, February 3, 2020) and has raised great concern all over the world and poses serious threat to global public health. , WHO raised the global COVID-19 risk to its highest level on February 28, 2020. Due to the joint efforts of all countries in the world, the epidemic has been well contained in some countries. However, the recent infections of COVID-19 began to increase and it is possible to usher in the second wave of the pandemic (Fig. 1 A). Most of the areas with increased infection are located in the northern hemisphere, which is now in a cold winter. It may suggest that the chance of infecting COVID-19 is associated with climate change. Though the exact relationship is unclear, we can find some seasonal impact on the spread of the coronavirus through the following cases.

Fig. 1

COVID-19 infection in different areas (updated on February 3, 2021). (A) Confirmed cases of COVID-19 all over the world. (B) Confirmed cases of COVID-19 in China. (C) Confirmed cases of COVID-19 in Australia. (D) Confirmed cases of COVID-19 in the United States.

Fig. 1 COVID-19 infection in different areas.

Case1: The SARS-CoV-2 was first detected in Wuhan, central China, but the government contained the epidemic by controlling the infection source, restricting population movement. In China, from mid-February to mid-November 2020, the number of new local infections per day dropped from nearly 1000 to less than 100. However, as the temperature drops in winter, the number of people infected with COVID-19 increases obviously, and many places become risk areas especially in Hebei, Beijing, Liaoning and Heilongjiang which are northern provinces in China with colder surrounding (Fig. 1B).

Case2: In March 2020, the COVID-19 began to spread in Australia. From March 24, 2020 to April 3, 2020, about 300 people were infected with COVID-19 every day. With the Australian government taking active measures, the epidemic situation has been effectively controlled and the number of infections per day was down to less than 20. Australia is located in the southern hemisphere, so it is winter from July to August every year. Between July and August 2020, COVID-19 re-emerged in some cities. Furthermore, compared with the first wave, the second wave of the epidemic infected more people and covered a wider range of areas. Interestingly, with the increase in temperature since August, the number of people infected with COVID-19 has decreased (Fig. 1C).

Case3: The number of people infected in the United States has exceeded 26 million, accounting for 1/4 of the total global infections. Therefore, the data of COVID-19 infection in the United States are representative. At the beginning of 2020, due to the fact that the United States regards COVID-19 as influenza, the number of people diagnosed with infection is relatively small. However, From the end of March 2020 to the present, February 3, 2021, the number of people infected with COVID-19 in the United States is increasing with the cooling of the environment (Fig. 1D).

All three cases demonstrate that there is a certain link between different climates and the risk of infection with COVID-19. On the one hand, the air is dry in winter, which can easily cause respiratory symptoms, such as runny nose, sneezing and coughing, on the other hand, coronaviruses can survive longer in cold environments. In this case, the virus released in the air after sneezing or coughing can survive longer. Therefore, the chilly climate may increase the chance of infecting COVID-19.

In brief, the COVID-19 pandemic has created major challenges for medical and health departments globally. Everyone should take precautions against the COVID-19, particularly in winter.

Declaration of Competing Interest

The authors state that they have no competing interests.