Does Warm Weather Affect the Spread of COVID-19?

Does Warm Weather Affect the Spread of COVID-19?

Since the start of the COVID-19 outbreak, several theories have been formulated about the sensitivity of the virus to heat.

Many have supported the idea that the novel coronavirus could be susceptible to heat, hoping for its gradual disappearance as the season changes. The media have also been circulating this idea, giving hope to people.

However, a theory remains a theory until proven otherwise; therefore, it is very important to carry out experiments to understand if this theory holds true or not.

Assumptions

Since the beginning of March, the majority of positive cases have mainly been concentrated in the area stretching along the 30-50° N’ corridor, where the climate was mild (end of winter). For this reason, it was originally suggested that the virus could be influenced by climate, and that it would decrease significantly with the arrival of spring and warmer weather. The fact that this pattern is typical of many viruses affecting the human respiratory system (including SARS) has certainly influenced this theory.

However, recent data has revealed the spread of the virus in other areas such as the tropics, where the temperature is warm. Some of these countries are Indonesia, Singapore, and Brazil. The same has occurred in the Southern Hemisphere, in countries such as Australia and Argentina.

Therefore, the current distribution of outbreaks goes against the idea that the novel coronavirus could behave like a seasonal respiratory virus.

To get a clearer picture, in China, scientists studied the relationship between the apparent exponential rate of the spread of the novel coronavirus and the basic reproduction number of the infection (R0), against the average daily temperature.

Remark: The R0 factor represents the average number of individuals infected by a positive individual during his or her infection period, assuming that every other individual in the population is susceptible to the virus.

 

Experimental method used

Firstly, the necessary data was collected:

    • Clinical and epidemiological data: dated from 31st December 2019 to 26th March 2020; based on WHO reports, the European Center for Disease Prevention and Control (ECDC), and the Johns Hopkins University Center for Systems Science and Engineering (JHU CSSE).
    • Temperature data: the average temperature in February and the first three weeks of March were recorded in the capitals of the various nations, and considered as a reference for the whole country.

Based on the data collected, a study was then carried out to determine whether the increase in temperature affects the spread of the virus.

Comparison of the collected data

In the image below, we can see R0 in relation to the different average global temperatures.

At first glance, note how the values taken into consideration are not related to each other.

 

R0-stati

temperatura-media-stati

For example, in very hot places like South America and Indonesia, the R0 is lower than much colder countries like North America and Europe. At the same time, cold countries like Ukraine and Turkey have much higher R0 than warmer countries like Australia.

Findings

At the end of the study, the findings show that there is no relationship between the ambient temperature and virus transmission. What had previously been theorized has not been validated by evidence.

Thus far, there is no evidence to suggest that the transmission of the virus is temperature-dependent. This observation applies to the temperature range between -10°C and +31°C.

Unfortunately, to date, it remains unproven that SARS-CoV-2 behaves like a seasonal virus.

 

 

Med4Care Marco De Nardin

Dr De Nardin, MD

 

Sources:

  • Tahira Jamil, Intikhab Syed Alam, Takashi Gojobori, Carlos Duarte. No Evidence for Temperature-Dependence of the COVID-19 Epidemic. doi: https://doi.org/10.1101/2020.03.29.20046706 
  • Gaunt, E.R., Hardie, A., Claas, E.C., Simmonds, P., and Templeton, K.E. (2010). Epidemiology and clinical presentations of the four human coronaviruses 229E, HKU1, NL63, and OC43 detected over 3 years using a novel multiplex real-time PCR method. Journal of clinical microbiology 48, 2940-2947. 
  • Sajadi, M.M., Habibzadeh, P., Vintzileos, A., Shokouhi, S., Miralles-Wilhelm, F., and Amoroso, A. (2020). Temperature and latitude analysis to predict potential spread and seasonality for COVID-19. Available at SSRN 3550308. 
  • Tan, J., Mu, L., Huang, J., Yu, S., Chen, B., and Yin, J. (2005). An initial investigation of the association between the SARS outbreak and weather: with the view of the environmental temperature and its variation. Journal of Epidemiology & Community Health 59, 186-192. 
  • Wang, M., Jiang, A., Gong, L., Luo, L., Guo, W., Li, C., Zheng, J., Li, C., Yang, B., and Zeng, J. (2020). Temperature significant change COVID-19 Transmission in 429 cities. medRxiv.

 

 

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Virus: che cos’è e come funziona
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