COVID-19 and its association with meteorological, climate, and environmental factors: An umbrella review

SeyedAlinaghi et al., Journal of Public Health Research, doi:10.1177/22799036251358298, Jul 2025
Sunlight for COVID-19
35th treatment shown to reduce risk in December 2021, now with p = 0.0000011 from 6 studies.
Lower risk for mortality, hospitalization, recovery, and cases.
No treatment is 100% effective. Protocols combine treatments.
6,600+ studies for 220+ treatments. c19early.org
Umbrella review of 9 systematic reviews covering 298 studies on the association between meteorological, climate, and environmental factors and COVID-19 transmission and mortality.
Sunlight/UV radiation showed a negative correlation in two studies. Higher temperatures were negatively associated with COVID-19 spread and mortality in 6 of 9 studies, with viral inactivation occurring at 25°C-30°C and increased infectivity at 5°C. Higher humidity was negatively correlated with COVID-19 transmission and mortality in 7 of 9 studies, with a relative humidity of 50%-70% proposed as reducing airborne viral load. Air pollution, particularly long-term PM2.5 and NO2 exposure, was associated with higher COVID-19 mortality, although evidence was uncertain for short-term exposures. Precipitation showed no significant association in three studies.
Reviews covering sunlight for COVID-19 include1-5.
Currently there are 6 sunlight studies and meta-analysis shows:
OutcomeImprovement
Mortality41% lower [28‑51%]
Hospitalization32% lower [6‑50%]
Cases48% fewer [11‑70%]
SeyedAlinaghi et al., 25 Jul 2025, peer-reviewed, 17 authors. Contact: es.mehraeen@gmail.com.
Abstract: 20252025 review-article 1358298 Systematic reviews & meta-analyses Journal o f Public Health Research COVID-19 and its association with meteorological, climate, and environmental factors: An umbrella review https://doi.org/10.1177/22799036251358298 Journal of Public Health Research 2025, Vol. 14(3), 1 -13 © The Author(s) 2025 DOI: 10.1177/22799036251358298 journals.sagepub.com/home/phj , SeyedAhmad SeyedAlinaghi 1 , Arian Afzalian 2 , Hengameh Mojdeganlou 3 , Sanaz Varshochi 2 , Parinaz Paranjkhoo 4 , Parmida Shahbazi 5 , Mina Hajizadeh 6 , Sohrab Lotfi 7 , Amirhassan Hajei 7 , Khadijeh Nasiri 8 , Amir Masoud Afsahi 9 , Fatemeh Afroughi 2,10 , Ladan Heidaresfahani 7 Amirali Karimi 2 , Narjes Sadat Farizani Gohari 11 , Esmaeil Mehraeen 12 and Daniel Hackett 13 Abstract COVID-19 transmission can be influenced by various factors, including weather and climate conditions, population density, and the availability of medical facilities. To gain a deeper understanding of this topic, an in-depth analysis of recent studies is needed. Our objective was to investigate previous systematic reviews that have examined the seasonal variation of COVID-19 and the impact of climate on its transmission and mortality. Online databases that included PubMed, Scopus, Web of Science, and Cochrane were searched using relevant keywords up to November 2021. Negative associations were found between temperature and COVID-19 spread and mortality (6/9 studies, 66.6%). These negative correlations imply a decrease in the spread and mortality of COVID-19 with an increase in temperature. Similarly, seven systematic reviews reported a negative correlation between humidity and transmission or mortality of COVID-19 (7/9 studies, 77.7%). COVID-19 spread was not associated with precipitation (three studies) but was negatively correlated with sunlight or UV radiation (two studies), COVID-19 incidence and mortality were positively associated with wind speed (one study). One study reported that the effect of air pressure and UV radiation on COVID-19 activity was unknown. The effects of air pollution, seasonal changes, wind speed, precipitation, and UV radiation on COVID-19 incidence or mortality remain unclear. However, factors proposed as having the greatest influence on COVID-19 incidence or mortality include air pollution, wind speed, and wastewater. Sunlight exposure and warm climates likely assist with reducing COVID-19 incidence or mortality, with the infection having a winter seasonality. Keywords COVID-19, SARS-CoV-2, season, seasonal variation, temperature, weather Received: 5 September 2023; accepted: 25 June 2025 1 Iranian Research Center for HIV/AIDS, Iranian Institute for Reduction of High-Risk Behaviors, Tehran University of Medical Sciences, Tehran, Iran 2 School of Medicine, Tehran University of Medical Sciences, Tehran, Iran 3 Department of Pathology, The Johns Hopkins University School of Medicine, Baltimore, USA 4 Turpanjian College of Health Sciences, American University of Armenia, Yerevan, Armenia 5 Orthopedic Department, Orthopedic Surgery Research Center (OSRC), Sina Hospital, Tehran University of Medical Sciences, Tehran, Iran 6 Faculty of Advanced Science and Technology, Department of Microbiology, Tehran University Medical Science, Islamic Azad University, Tehran, Iran 7 School of Medicine, Islamic Azad University, Tehran, Iran 8 Department of Nursing, Khalkhal University of Medical Sciences,..
DOI record: { "DOI": "10.1177/22799036251358298", "ISSN": [ "2279-9036", "2279-9036" ], "URL": "http://dx.doi.org/10.1177/22799036251358298", "abstract": "<jats:p>COVID-19 transmission can be influenced by various factors, including weather and climate conditions, population density, and the availability of medical facilities. To gain a deeper understanding of this topic, an in-depth analysis of recent studies is needed. Our objective was to investigate previous systematic reviews that have examined the seasonal variation of COVID-19 and the impact of climate on its transmission and mortality. Online databases that included PubMed, Scopus, Web of Science, and Cochrane were searched using relevant keywords up to November 2021. Negative associations were found between temperature and COVID-19 spread and mortality (6/9 studies, 66.6%). These negative correlations imply a decrease in the spread and mortality of COVID-19 with an increase in temperature. Similarly, seven systematic reviews reported a negative correlation between humidity and transmission or mortality of COVID-19 (7/9 studies, 77.7%). COVID-19 spread was not associated with precipitation (three studies) but was negatively correlated with sunlight or UV radiation (two studies), COVID-19 incidence and mortality were positively associated with wind speed (one study). One study reported that the effect of air pressure and UV radiation on COVID-19 activity was unknown. The effects of air pollution, seasonal changes, wind speed, precipitation, and UV radiation on COVID-19 incidence or mortality remain unclear. However, factors proposed as having the greatest influence on COVID-19 incidence or mortality include air pollution, wind speed, and wastewater. Sunlight exposure and warm climates likely assist with reducing COVID-19 incidence or mortality, with the infection having a winter seasonality.</jats:p>", "alternative-id": [ "10.1177/22799036251358298" ], "article-number": "22799036251358298", "author": [ { "affiliation": [ { "name": "Iranian Research Center for HIV/AIDS, Iranian Institute for Reduction of High-Risk Behaviors, Tehran University of Medical Sciences, Tehran, Iran" } ], "family": "SeyedAlinaghi", "given": "SeyedAhmad", "role": [ { "role": "author", "vocabulary": "crossref" } ], "sequence": "first" }, { "affiliation": [ { "name": "School of Medicine, Tehran University of Medical Sciences, Tehran, Iran" } ], "family": "Afzalian", "given": "Arian", "role": [ { "role": "author", "vocabulary": "crossref" } ], "sequence": "additional" }, { "affiliation": [ { "name": "Department of Pathology, The Johns Hopkins University School of Medicine, Baltimore, USA" } ], "family": "Mojdeganlou", "given": "Hengameh", "role": [ { "role": 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