COVID-19: Temperature significantly changes COVID-19 transmission in 429 cities

Temperature significantly changes COVID-19 transmission in 429 cities. Spencer EA, Heneghan C.

Published on July 2, 2020

Reference Wang M, Jiang A, Gong L, Luo L, Guo W, Li C, Zheng J, Li C, Yang B, Zeng J, Chen Y, Zheng K, Li H. Temperature significant change COVID-19 Transmission in 429 cities medRxiv 2020.02.22.20025791 2020
Study type
Country China
Setting Global
Funding Details Non reported
Transmission mode Meteorological
Exposures Temperature

Bottom Line

Lower weather temperatures were associated with higher COVID-19 transmission. There might be a most conducive temperature for the viral transmission, which may partly explain why it first broke out in Wuhan at that time.

Evidence Summary

A total of 24,139 confirmed cases were identified, in China and 26 additional countries: 16,480 cases (68%) in Hubei Province. 

Cumulative total confirmed cases correlated with average temperature, minimum temperature and maximum temperature. The association between temperature and case numbers was nonlinear. Cumulative total confirmed cases were highest at an average temperature of 8.7°C, and less at lower temperatures and more at higher temperatures. 

What did they do?

The study authors collected the cumulative number of confirmed cases of all cities and regions affected by COVID-19 worldwide from 20th January to 4th February 2020. 

Using data for capital cities from countries’ meteorological authorities, they calculated the daily means to represent each country’s average, minimum and maximum temperatures throughout January. 

They assessed the relationships between temperature and case numbers using a restricted cubic spline function and generalized linear mixture models were used to estimate a dose-response relationship.

Study reliability

This is a cross-sectional study and does not prove causation. Other confounding factors may be responsible for the observed associations. The time frame is also too short based on the prolongation of the outbreak

Clearly defined setting Demographic characteristics described Follow-up length was sufficient Transmission outcomes assessed Main biases are taken into consideration
Yes No No No No

What else should I consider?

If this observed association is causal, warm summer temperatures of around 30°C should slow transmission markedly. Equally, winter temperatures of between 0 and 10°C would increase risk again, although very low winter temperatures below freezing should slow transmission.

About the authors

Carl Heneghan

Carl is Professor of EBM & Director of CEBM at the University of Oxford. He is also a GP and tweets @carlheneghan. He has an active interest in discovering the truth behind health research findings

Elizabeth Spencer

Dr Elizabeth Spencer; MMedSci, PhD. Epidemiologist, Nuffield Department for Primary Care Health Sciences, University of Oxford.