Table 4.

Selected literature on global epidemiological analyses regarding COVID-19 spread and temperature/humidity.

Region	Timespan	Meteorological variables	Outcome variable	Confounding variables	Study Type∗	Inferences	References
3739 global locations	December 12, 2019 to April 22, 2020	Temperature, humidity, precipitation, snowfall, moon illumination, sunlight hours, ultraviolet index, cloud cover, wind speed and direction, pressure data	Effective reproduction number	Air pollutants, population density, and using models to control for estimating effective reproduction number	b	A moderate negative (coefficient: 0.037% with 95% CI of 0.019–0.054) relationship between the estimated reproduction number and temperatures above 25 °C was obtained	[3]
277 global regions	December 1, 2019 to April 14, 2020	Humidity, temperature, wind speed, and visibility data	Defined growth rate	Location, population, people aged over 65, area, life expectation, the number of hospital beds, GDP, and governmental policy	a	Temperature sensitivity of COVID-19 spread was only −2.7% (−5.2%–0%), indicating warm summer is unlikely to eliminate COVID-19 transmission naturally	[2]
1236 regions	By the end of May 2020	Daily mean temperature and humidity	New daily case and basic reproductive number	Gross regional product, population, government response, elevation and suspected population, working population, and school-age group	b	Temperature and relative humidity were negatively associated with the COVID-19 spread	[114]
409 cities across 26 countries	January 1, 2020 to May 31, 2020	Temperature, dewpoint temperature, surface solar radiation, downwards, precipitation, and wind	Effective reproduction number	Government response index, total population, population density, the elderly population (>65 years), and GDP and PM2.5	a	Meteorological conditions influenced little COVID-19 spread. Population behavior and government interventions were more important drivers of transmission.	[78]
202 locations in 8 countries	As of the early stage of the global pandemic	Daily temperature, humidity, and UV radiation	Basic reproductive number	–	b	Meteorological conditions did not statistically alter the COVID-19 spread	[72]
Global, first-level administrative division	As of March 17, 2020	Daily temperature and humidity	Confirmed cases	Exposure day; the median age of the national population, population density, the capacity of the country to detect an emerging infectious disease	b	A negative association with COVID-19 incidence for temperatures of −15 °C and above was found	[76]
Global	Data on April 2, 2020	Temperature	Proportion of cases	GDP, latitude, and longitude	a	The temperature may be negatively associated with both the proportions of COVID-19 cases/mortalities in the population	[75]
50 cities	From at least 10 reported deaths in a country to March 10, 2020	Mean temperature and humidity	Total number of cases	–	a	The distribution of substantial community outbreaks along restricted latitude, temperature, and humidity measurements was consistent with the behavior of a seasonal respiratory virus.	[115]
144 geopolitical areas worldwide, excluding China, South Korea, Iran, and Italy	From at least 10 COVID-19 cases to March 20, 2020	Temperature and humidity	Epidemic growth rate	Elevation, GDP, health expenditure as a percent of GDP, life expectancy, rate of people aged over 65 years or older, the infectious disease vulnerability index, urban population density, number of flight passengers per capita, and closest distance to a country with an already established epidemic	a	COVID-19 spread was not associated with temperature but maybe weakly and negatively associated with humidity.	[77]
249 countries	December 1, 2019, to March 30, 2020	Daily data of precipitation, average temperature, maximum temperature, and minimum temperature	COVID-19 transmission and deaths	Exposure time, population density, and dummy month	b	The average temperature per country was negatively associated with the number of cases of SARS-CoV-2 infections	[116]
More than 200 countries	Counts on specific days	Monthly average temperature	COVID-19 cases	–	a	The temperature may be negatively associated with COVID-19 transmission	[73]
166 countries, excluding China	As of March 27, 2020	Temperature, humidity, wind speed	Daily new cases and deaths	The median age of the national population, population density, global health security, human development index, and exposure day	b	The temperature may be negatively related to COVID-19 transmission	[74]
Global, top 20 countries	January 22 to April 27, 2020	Daily Temperature, dew/frost point, wind speed, precipitation, relative humidity, surface pressure	COVID-19 outcomes	–	b	High temperature and high relative humidity reduced the viability, stability, survival, and transmission of COVID-19, whereas low temperature prolonged the activation and infectivity of the virus	[117]
Global	The number of reported cases and deaths in April 2020	Temperature and humidity	Reported positive cases and deaths	Human development index	a	Surface air temperature and Specific humidity do not have any statistically significant association with COVID-19 transmission, though there is a weak relationship between temperature and the pandemic’s mortality	[118]
Global	January to April, 2020	Temperature, humidity, and UV	Growth rate	Population data	a	Without intervention, COVID-19 will decrease temporarily during summer, rebound by autumn, and peak next winter	[119]
Global, 209 countries	In the first 16 weeks of the infection	Climatic zone, temperature, solar irradiation, relative humidity, wind speed, surface pressure, precipitation	COVID-19 Incidence or prevalence	population size, land area	a	Climatic factors significantly influence the spread of SARS-CoV-2	[120]
Global, 52 countries	December 31, 2019, to April 13, 2020	Temperature, relative humidity, and solar radiation	Basic reproduction number	Global Health security index	a	A negative association is found between the incidence of COVID-19 and temperature.	[121]
Global, 206 regions/countries	January 8, 2020 to April 20, 2020.	Temperature, relative humidity, UV index, wind speed, cloud cover, precipitation, sea-level air pressure, and daytime length	newly reported COVID-19	GDP per capita, and the Global Health Security Index	b	The positive association between COVID-19 and 14-day lagged temperature and a consistently higher rate of COVID-19 cases in absolute humidity of 5–10 g/m3	[122]
35 OECD countries and all US states	–	Ambient temperature, relative humidity, cumulative precipitation, and air pollution	COVID-19 mortality	Population size, population density, days of social distancing prior to first reported COVID-19 death, the Gini index as a measure of socioeconomic inequality, ICU beds, the prevalence of obesity, smoking prevalence, and proportion of the population older than 75 years.	a	A 1 °C increase in ambient temperature was associated with 6% lower COVID-19 mortality at 30 days following the first reported death	[96]
Global, 159 countries	January 22 to June 15, 2020	Air temperature, specific humidity	Growth rate	Population density, size, and structure, per capita government health expenditure, and global airport connection	a	The role of environmental conditions on COVID-19 transmission is controversial.	[123]
Global, 188 countries	As of 31 December 2020	Mean temperature, maximum temperature, minimum temperature, dew point temperature, precipitation, and wind speed	The number of daily new cases	Population density, government response stringency index, human development index, categorical variable for the country, and date	b	The mean temperature, wind speed, and relative humidity were negatively correlated with daily new cases of COVID-19,	[124]
Global	–	UV radiation, temperature, specific humidity, and precipitation	The daily growth rate of confirmed COVID-19 cases	Social and economic characteristics	a	Temperature and specific humidity cumulative effects are not statistically significant	[125]
144 countries	At least 21 days of death until April 27, 2020.	Maximum temperature, relative humidity, and UV Index	COVID-19 mortality rates	Population structure, the number of hospital beds, governmental immigration restrictions, and GDP	a	The temperature has a negative association with the COVID-19 mortality rate.	[126]
47 countries	February 22 to June 22, 2020	Temperature, air pressure, and wind speed	Effective reproductive number	Human mobility, country, and date	b	A negative relationship between temperature and COVID-19 transmission rate	[127]
615 cities	January to June 2020	Temperature, pressure, humidity, dew, wind gust	Total number of COVID-19 confirmed cases	–	b	High ambient temperature and relative humidity have a mitigation effect on COVID-19.	[128]
153 countries	January to May 2020	Temperature, humidity, air pressure, wind speed, precipitation	Daily COVID-19 cases, basic reproductive number	Day, policy	b	The temperature was positively related to daily new cases at low temperature but negatively related to daily new cases at high temperature	[129]
191 countries	Until January 22, 2021	Temperature	Mortality rate	Daily test, political regime, urban population, GDP, air pollutant, and DALYs	a	Mean annual temperature showed a significant inverse association with the COVID-19 mortality rate	[130]
150 countries	A minimum of 90 days since the first confirmed case	Temperature	Mortality rate	The probability of mortality due to respiratory disease, the stringency of government measures, countries’ hemisphere, DALYs, human development index, population density, and the proportion of people aged 65 and older	b	The increase in ambient temperature decreases the incidence of COVID-19 deaths	[131]
58 countries, at least 30 daily cases as of July 29, 2020	–	Temperature, precipitation	Basic reproduction number	Demographics, disease, economics, air pollution, habitat, health, and social factors	a	Temperature and humidity did not have strong relationships with R0 but were positive.	[132]

∗ a, cross-sectional study; b, longitudinal study.