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 Table of Contents  
Year : 2021  |  Volume : 8  |  Issue : 2  |  Page : 151-154

Impact of environmental factors on COVID-19 pandemic: A narrative review

1 Rangaraya Medical College, Kakinada, Andhra Pradesh, India
2 Konaseema Institute of Medical Sciences and Research Foundation (KIMS & RF), Amalapuram, Andhra Pradesh, India
3 Andhra Medical College, Visakhapatnam, Andhra Pradesh, India
4 Prathima Institute of Medical Sciences, Karimnagar, Telangana, India

Date of Submission07-Feb-2021
Date of Acceptance08-Apr-2021
Date of Web Publication02-Jun-2021

Correspondence Address:
Dr. Tarun Kumar Suvvari
Rangaraya Medical College, Pithampuram Road, Kakinada 533001, Andhra Pradesh.
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/mgmj.mgmj_10_21

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The World Health Organization declared COVID-19 disease as a pandemic after the first cases from China were reported in December 2020. COVID-19, caused by SARS-CoV2 (severe acute respiratory syndrome), spreads by contact with infected droplets. The incubation period ranges from 2 to 14 days with initial symptoms of fever, sore throat, cough, fatigue, malaise, and breathlessness. In patients with co-morbidities and the elderly, it progresses to pneumonia, acute respiratory distress syndrome, and multi-organ failure. Regarding the impact of the environment on the spread of the corona virus, more research is going on. Environmental factors including atmospheric temperature, ventilation, climate change, and humidity have been studied to understand the effect of these factors on COVID-19 spread. We have evaluated studies to date related to the environmental effect on COVID-19 and summarized them for better understanding.

Keywords: Air pollution, COVID-19, environment, humidity, temperature

How to cite this article:
Suvvari TK, Kutikuppala LV, Jonna S, Kashif MS. Impact of environmental factors on COVID-19 pandemic: A narrative review. MGM J Med Sci 2021;8:151-4

How to cite this URL:
Suvvari TK, Kutikuppala LV, Jonna S, Kashif MS. Impact of environmental factors on COVID-19 pandemic: A narrative review. MGM J Med Sci [serial online] 2021 [cited 2022 Sep 28];8:151-4. Available from: http://www.mgmjms.com/text.asp?2021/8/2/151/317441

  Introduction Top

The recent novel coronavirus (COVID-19) has caused devastating consequences in the world. The outbreak originated from Wuhan, Hubei Province, China, in late December 2019. Considering the devastating effect the virus has on society’s social well-being and economy, the World Health Organization declared an international public health emergency on January 30, 2020.[1]

As of October 31, 2020, 46,393,367 cases have been reported with 1,200,384 deaths worldwide.[2] In India, 81,37,119 cases have been confirmed; the death rate is 1.49%, which is lower than in many countries.[3] Studies revealed that COVID-19 identified respiratory droplets to be the most common mode of transmission. The symptoms of COVID-19 are similar to other coronavirus diseases such as SARS and MERS, which include high fever, dry cough, difficulty in breathing, and advanced stage kidney failure and pneumonia, ultimately leading to respiratory failure and death.

The effect of environmental factors is significant on COVID-19 transmission and control. We compared various environmental factors such as temperature, humidity, seasonal variations, climate, etc., on COVID-19 along in this paper.

Overview of impact of climate change in COVID-19

Experiments suggest that SARS-CoV2 on the surface or in the air is sensitive to UV light, temperature, and moisture content.[4] The UV light is from germicidal UV radiations (UV-C) used in hospitals and laboratories, but this being misunderstood as UV in sunlight (UV-A and UV-B) can kill the virus. Newer experiments support the hypothesis that sunlight impacts reducing transmission, but only a 1% reduction is seen.[5] Other respiratory viruses are seasonal and frequently occur in winter: influenza and common cold show seasonal transmission in correlation to the weather condition.

Research shows that there should be some long-lasting immunity to have stable changes or seasonal epidemic waves as we observe with influenza.[6] During the first wave of the 2009 H1N1 pandemic, cases went up till August, the most environmentally unfavorable point of the year with only 20% immunity. After months, immunity and environment sensitivity caused a winter-driven third wave, a study showed.[7] Scientists anticipate that a warmer climate would not have any protective impact with current susceptibility to the virus.

The current scenario in India

The spread of COVID-19 was exponential from 3 March to 5 April 2020, followed by a quadratic regression from April 6 to 2 May 2020. Linear growth is observed from 3 May to 15 May. After May 15, we see a spike in the cases followed by another spike from 1 June to 11 July, which may be due to the relaxation of lockdown measures. A positive correlation was observed among daily transmission, air temperature, and wind speed. O3 shows a positive correlation to Covid-19 cases spike.[8]

With winter and Covid-19, global health experts raise concerns over the second wave of the pandemic, which can worsen the huge rise of COVID-19 cases in the UK due to the onset of winter. Winter is the flu season, and there is a high possibility that people may contract both influenza and the COVID-19 infection, resulting in devastating consequences. The rise in pollution levels in India’s major cities due to festivals and unlocking measures would coincide with winter, leading to an increase in cases. With the government’s festive season around and more unlocking measures and the season of stubble burning, joints push the air quality index toward hazardous levels. Severe air pollution can lead to breathing issues in Covid-19 patients, which is another major concern. Cold air is denser and can form a long-lasting cap in the sky, keeping us exposed longer. So, air pollution worsened Covid-19, and a dip in mercury is a looming threat our lungs will have to fight against.

Effect of atmospheric temperature

Respiratory viruses survive better in cold to dry weather. The immune system of humans is reduced due to less availability of vitamin D and melatonin. Another factor is that people tend to stay indoors more during winter, which can lead to the indoor spread of Covid-19 if proper precautions of self-isolation are not considered. There are scientific papers that provide a correlation between the spread of droplets and temperature. The droplets from a cough or sneeze evaporate with higher temperatures, hence the low infectivity.[9],[10],[11],[12]

Effect of ventilation

Closed areas with less ventilation can increase the risk of Covid-19 transmission. Analysis of the spread of Covid-19 in Wuhan indicates that close contact is necessary for its transmission. The spread is broadly limited to family members, close contacts, and healthcare professionals. For individuals at high risks, e.g. older people, individuals with diabetes, or immune-compromised conditions, if they get exposed to even a small number of people in a closed space, e.g. airplane, centralized A/c, the chances of transmission are significantly high.[9],[10],[11],[12]

Effect of humidity

Humidity is the water vapor concentration present in the air. It was observed that dried viruses on smooth surfaces retained their viability at lower humidity. Geographical areas with higher temperature and humidity reduced the viability of the virus. High temperature and high humidity hurt Covid-19 transmission.[9],[10],[11],[12]

Air pollution versus Covid-19

In a study by Pozzer et al.,[13] it was estimated that nearly 15% of global deaths of Covid-19 are due to long-term exposure to air pollution. The proportion was 27% in East Asia, 19% in Europe, and 17% in North America. The number of deaths due to COVID-19 because of air pollution can be reduced if they were not exposed to anthropogenic emissions. Suppose we see an individual country’s contribution to COVID-19 deaths due to air pollution. In that case, Czech Republic tops with 29%, followed by China (27%), Germany (26%), Italy (15%), the UK (14%), and the lowest by New Zealand (1%).

The above-obtained data were interpreted by the epidemiological data from previous studies on air pollution and COVID-19 by the USA, China, and the SARS outbreak in 2003. The data were combined with satellite data showing global exposure to “particulate matter” that was less than or equal to 2.5 µm in diameter (PM2.5). The data interpreted into results were epidemiological data collected till the 3rd week of June 2020. The particulate matter could increase the activity of angiotensin-converting enzyme 2 (ACE-2) receptors on the cell surfaces and damage the lungs, leading to higher chances of getting infected with the virus and may develop systemic complications. The pandemic can be controlled with the vaccine or herd immunity. Still, sadly there are no vaccines for air pollution and environmental changes.[13]

Overview on seasonality of COVID-19?

The answer for that would be based on the seasonality of other human coronaviruses and influenza A, in vivo experiments with influenza transmission, ecological data, and the observed epidemiology of COVID-19 in the various parts of the globe during summer and early fall. When we compare various respiratory viral pathogens, human alpha and beta coronaviruses and influenza show a high peak during the winter months. The rise in the cases is thought to be due to the effect of the environment on viral stability, transmission, behavior changes of humans, and changes in the humans’ immunity level. Winter months are usually associated with lower temperatures, lower absolute humidity, and lower indoor relative humidity. More specifically, an increase in influenza and coronavirus stability and transmissivity is highly associated with cool, dry environments.[14]

Several scientists worked to rule out the relation between viral propagation and environmental factors through controlled laboratory settings and natural history observations. Before March 22, 2020, 90% of the global transmission of SARS-CoV-2 had occurred in areas with temperatures ranging from 3°C to 17°C and absolute humidity ranging between 4 and 9g/m3 daily.[14]

A study by Rucinski et al.[15] on seasonality of coronaviruses 229E, HKU1, NL63, and OC43 between April 1, 2014 and March 31, 2020 consists of 8839 tests, with a mean of 123 tests per month revealed 3234 (37%) positive results for at least one target on the panel. About 326 (4% overall) were positive for any coronavirus 229E, HKU1, NL63, and OC43. The seasonality was detected for all four coronaviruses. Higher rates were observed in winter and early spring and lower summer and early fall.

There are various practical reasons for the seasonality of coronavirus OC43, NL63, 229E, and HKU1 due to variation in temperature, humidity, and human behavioral changes. Coronaviruses are heat-sensitive with a lower survival rate at higher temperatures. Low humidity can lead to dry mucosal membranes, increasing susceptibility to infection from respiratory viruses and giving rise to delayed settling of respiratory droplets. Human behavioral changes include heavy crowding at places with lower temperatures, not following necessary precautions, and not having serious lockdowns implemented during winter.[15]

  Conclusion Top

Although previous research works and current data suggest the effect of temperature and humidity on viral viability and transmission, the data are limited on the evolving pandemic; the seasonality of COVID-19 is yet to be concluded. But as more research is being done, the results should be considered, and public health measures should be changed to decrease COVID-19 transmission. At higher temperatures, the droplets evaporate, causing lower infectivity. During winter, there are high chances of having another peak of cases, which was observed during past pandemics. Less ventilation causes more transmission due to lack of air circulation. High humidity reduces the viability of the virus, causing lower infectivity. Air pollutants, particulate matter, increase the activity of ACE-2 receptors, which leads to severe complications in patients with Covid-19. Measures to decrease air pollution should be taken to decrease the severity and mortality associated with Covid-19. Region-specific public health measures should be framed to minimize transmission.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Suvvari TK, Kutikuppala LV, Babu GK, Jadhav M Understanding the unusual viral outbreak: Coronavirus disease 2019. J Curr Res Sci Med 2020;6:3-10.  Back to cited text no. 1
Coronavirus Outbreak [Internet] [cited November 20, 2020]. Available from: https://www.worldometers.info/coronavirus/. [Last accessed on 2020 November 15].  Back to cited text no. 2
COVID-19 India Official Website [Internet] [cited November 20, 2020]. Available from: https://www.covid19india.org/. [Last accessed on 2020 November 15].  Back to cited text no. 3
Carlson CJ, Gomez ACR, Bansal S, Ryan SJ Misconceptions about weather and seasonality must not misguide COVID-19 response. Nat Commun 2020;11:4312.  Back to cited text no. 4
Schuit M, Ratnesar-Shumate S, Yolitz J, Williams G, Weaver W, Green B, et al. Airborne SARS-CoV-2 is rapidly inactivated by simulated sunlight. J Infect Dis 2020;222:564-71.  Back to cited text no. 5
Shaman J, Goldstein E, Lipsitch M Absolute humidity and pandemic versus epidemic influenza. Am J Epidemiol 2011;173:127-35.  Back to cited text no. 6
Gupta A, Pradhan B Impact of daily weather on COVID-19 outbreak in India. medRxiv. 2020. doi: 10.1101/2020.06.15.20131490  Back to cited text no. 7
Sharma VK, Nigam U Modeling and forecasting of Covid-19 growth curve in India. Trans Indian Natl Acad Eng 2020;5:697-710. https://doi.org/10.1007/s41403-020-00165-z  Back to cited text no. 8
Priyadarsini SL, Suresh M Factors influencing the epidemiological characteristics of pandemic COVID 19: A TISM approach. Int J Healthc Manag 2020;13:89-98.  Back to cited text no. 9
Chan KH, Peiris JS, Lam SY, Poon LL, Yuen KY, Seto WH The effects of temperature and relative humidity on the viability of the SARS coronavirus. Adv Virol 2011;2011:734690.  Back to cited text no. 10
Smit AJ, Fitchett JM, Engelbrecht FA, Scholes RJ, Dzhivhuho G, Sweijd NA Winter is coming: A Southern Hemisphere perspective of the environmental drivers of SARS-CoV-2 and the potential seasonality of COVID-19. Int J Environ Res Public Health 2020;17:5634. doi:10.3390/ijerph17165634  Back to cited text no. 11
Vinoj V, Gopinath N, Landu K, Behera B, Mishra B The COVID-19 spread in India and its dependence on temperature and relative humidity. Preprints2020. doi:10.20944/preprints202007.0082.v1  Back to cited text no. 12
Pozzer A, Dominici F, Haines A, Witt C, Münzel T, Lelieveld J Regional and global contributions of air pollution to risk of death from COVID-19. Cardiovasc Res 2020;116:2247-53.  Back to cited text no. 13
Kanzawa M, Spindler H, Anglemyer A, Rutherford GW Will coronavirus disease 2019 become seasonal? J Infect Dis 2020;222:719-21. doi:10.1093/infdis/jiaa345  Back to cited text no. 14
Rucinski SL, Binnicker MJ, Thomas AS, Patel R Seasonality of coronavirus 229E, HKU1, NL63, and OC43 from 2014 to 2020. Mayo Clin Proc 2020;95:1701-3.  Back to cited text no. 15

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