![]() ![]() Faced with the global pandemic of COVID-19, declared by World Health Organization (WHO) on March 11 th 2020, and the need to better understand the seasonal behavior of the virus, our team conducted this systematic review to describe current knowledge about the emergence and replicability of the virus and its association with different weather factors such as temperature and relative humidity. Nevertheless, there is still divergence in the literature about the effects of temperature and humidity on the viability and transmissibility of the coronavirus infection that appeared in 2019. ![]() This combination may trigger an impairment of the local and systemic antiviral defense mechanisms, leading to increased host susceptibility to the respiratory viruses in winter. It is supposed that high temperature and humidity, together, have a combined effect on inactivation of coronaviruses while the opposite weather condition can support prolonged survival time of the virus on surfaces and facilitate the transmission and susceptibility of the viral agent. Many etiological factors such as changes in host physiological susceptibility, immune system function, social behavior, and weather conditions have been suggested in this context. The mechanism underlying these patterns of climate determination that lead to infection and possible disease transmission is associated with the ability of the virus to survive external environmental conditions before staying in a host. The coronavirus can retain its infectivity up to 2 weeks in a low temperature and low humidity environment, which might facilitate the virus transmission in a community located in a subtropical climate. ![]() The seasonal nature in the outbreaks of respiratory virus infections is a common phenomenon, with peaks often occurring in low temperatures, during the winter months. Limited studies have investigated climate parameters as important factors that could influence the SARS-CoV-2 spread. The transmission can be affected by a number of factors, including population density, migratory flow, host immunity, medical care quality and, presumably, climate conditions (such as temperature and humidity). A notable feature of SARS-CoV-2 is its predilection for transmission in the health care setting and to close family and social contacts by different manners, such as droplets, close direct or indirect contact, but the relative importance of these routes of transmission is still unclear. This epidemic has caused a collapse on health care services and economies of affected countries, and the overall mortality rate was estimated to be 4.7%, but in elderly patients, aged 60 or above, it can increase to up 14.8%. Spread of SARS-CoV-2, like other respiratory viruses, namely its predecessor SARS-CoV, may be due to spread via droplets and contact, exposing the virus to external environmental conditions. The etiological agents have been confirmed as a new subset of coronaviruses. An outbreak of atypical pneumonia named COVID-19 caused by this virus has been reported, and the pattern of human-to-human transmissibility of the virus has occurred nationally and internationally. Ī new epidemic of Severe Acute Respiratory Syndrome (SARS) Coronavirus has emerged since December 2019, namely SARS-CoV-2 or COVID-19, in Wuhan, the capital of Hubei Province, China. They are classified into four main genus sub-groups known as Alphacoronavius, Betacoronavirus, Gammacoronavirus, Deltacoronavirus, and are able to infect human beings with an upper respiratory infections. The coronaviruses, Orthocoronaviridae sub-family, are so called for their crown-like spikes on the viral surface. Respiratory tract infections are the most common infections worldwide, representing a source of significant morbidity and a considerable economic burden to health care.
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