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The influences of seasons and weather on COVID-19

The season is thought to be related to the incidence of coronavirus disease 2019 / COVID-19. At the beginning of the appearance of COVID-19, most experts predicted that the new coronavirus, SARS-CoV-2, would not survive in hot temperatures. However, based on the evidence currently, the coronavirus has spread in all areas both in environments with hot and cold weather.

The influences of seasons and weather on COVID-19
Source image: https://weather.com

Seasonal Influence on the Spread of Infectious Diseases

The season is one of the factors that can influence the spread of several pathogenic viruses. One example is the influenza virus that causes seasonal flu. Influenza viruses can spread and survive well in low temperatures and humidity. The ideal temperature for influenza viruses is 5 degrees C.

In temperate and subpolar regions, influenza epidemics tend to have a higher incidence in winter, between November and March in the northern hemisphere and between May and September in the south. In the tropics and subtropics, influenza outbreak patterns are more diverse, where the highest incidence is during the rainy season.

One study states that of the six climate variables, only two factors can have a significant effect on the spread of influenza, namely the average temperature (5.54 ± 1.09%) and absolute humidity (5.94 ± 1.08%). Although it is not possible to determine which is purely statistically based, the results of the study support the conjecture of the important role of climate in the spread of influenza.

However, the seasonal factor in the influenza epidemic is still not very clearly understood until now. Because in addition to the viral factor itself, there are still other factors that increase the incidence of flu. In cold weather, the blood vessels in the upper respiratory tract mucosa tend to contract, so this is thought to make it difficult for leukocytes to get to the respiratory tract mucosa, making it difficult for the body's immune system to fight the flu-causing virus. In addition, the patient's immune system is also suspected to be more decreased in cold weather due to lack of vitamin D intake from exposure to sunlight, and the habits of individuals who prefer crowding to stay indoors. 

Effects of Temperature, Weather and Climate on Coronavirus (SARS and MERS)

The spread of the coronavirus (betacoronavirus class), such as SARS-CoV and MERS-CoV, is thought to be influenced by temperature, weather, and climate. Although there is not yet much evidence, the spread of the coronavirus is thought to have a seasonal pattern in natural hosts where seasonal changes can increase the risk of zoonotic transmission at certain times.

Severe Acute Respiratory Syndrome (SARS) was a major pandemic at the end of 2002 caused by the SARS-CoV coronavirus, which is a zoonotic virus whose natural reservoir is the moon's ferret. In addition to being transmitted through droplets, the SARS-CoV virus was also successfully isolated in feces with high viral load, making researchers suspect that this virus could also spread via fecal-oral. SARS-CoV has high stability in the environment, which can last 2-3 days at room temperature on a contaminated dry surface, and 2-4 days in feces.

A study in Hong Kong in 2003 tried to identify the factors involved in the spread of the SARS-CoV virus. This study suggests that the highest incidence of SARS occurs in winter and gradually decreases as spring enters. This pattern looks similar to the seasonal pattern in influenza. From the same study, each increase in air temperature of 1 degree C is thought to be related to a decrease in the average incidence of 3.6 cases. However, the effects of temperature and air humidity can be disturbed by other factors, so further research is needed on the impact of seasons on the SARS epidemic.

Since 2012, many studies have analyzed the epidemiology, mode of transmission, and severity of Middle East Respiratory Syndrome (MERS). A cross-over study showed that the risk of transmission of MERS zoonoses from dromedary animals to humans or spread from asymptomatic careers tends to experience a significant increase in high temperatures and low/dry humidity.

Research shows that the coronavirus that causes MERS can survive up to temperatures of 30 degrees C. This is different from the viruses that cause other respiratory diseases, which generally only survive at low temperatures. Also, the presence of sandstorms and high levels of air pollution are known to be associated with increased respiratory disease morbidity and mortality in Saudi Arabia. Sandstorms can become pathogenic careers and trigger inflammatory reactions.

One study said the pattern of spread and severity of MERS looked different between countries in the Middle East and South Korea, where mortality to be higher in Middle Eastern countries. The spread process also looks different. In the Middle East, the spread process more often dromedary to humans. Whereas in South Korea, the spread is suspected from nosocomial infections. Other factors could also bias the effect of the season on MERS. 

Prediction of the Effects of Temperature, Weather, and Climate on COVID-19

Currently, several studies predict the effect of temperature, weather, and climate on the incidence of COVID-19. Some of these studies show that countries located at high latitudes, or farther from the equator, have a higher vulnerability to COVID-19 spread compared to tropical countries. These studies also find that the ideal condition for the spread of the coronavirus is temperatures around 8-10 degrees C with 60-90% humidity.

Some studies suspect that the combination of temperature, humidity, and wind speed might have a role in the spread of COVID-19. Low temperature and humidity are environmental conditions that are very conducive to the survival of the virus. Besides the potential to extend the half-life and viability of the coronavirus, other potential mechanisms associated with low temperature and humidity are droplet stabilization and the speed of spread in the nasal mucosa.

One study by Bannister-Tyrrell et al. in 2020 found a negative correlation between temperatures above 1 degree C to the number of suspected COVID-19 cases per day. This study showed that the optimum distribution of COVID-19 is at shallow temperatures, 1-9 degrees C. This means that the higher the temperature, the lower the COVID-19 cases. The results of the study concluded that the tropical climate could actually help inhibit the spread of the coronavirus because tropical climate conditions can actually make the virus more quickly become unstable. However, the results of this study still need to be further evaluated.

In addition, lifestyle changes may be another factor that contributes to the increasing population at risk. For example, an increase in international travel causes the coronavirus to spread throughout the world on a massive scale. Weather and climate maybe some of the contributing factors for the COVID -19 outbreak when it first appeared in high latitude countries. But, the increase in second wave cases is likely to be more influenced by the level of human mobility and social interaction.

Certain seasonal patterns such as temperature and humidity may have a role in the spread of COVID-19, but until now, there has been no conclusive research. Several studies related to the influence of seasons on influenza disease show seasonal patterns, especially in temperate and subpolar regions. This condition is suspected because the cold temperature factor can cause a decrease in defense of the nasal mucosa barrier, lack of vitamin D intake from a little sun exposure, as well as lifestyle changes of people who prefer crowding indoors.

Research on the season's effects on the SARS and MERS spread has also been carried out. The SARS incidence is higher when temperatures and humidity decrease in temperate regions, while MERS increases in hot and dry regions such as Saudi Arabia. However, the results confidence level of existing studies is still relatively low, given the very limited epidemiological data and the short research time.

An increase in the second wave of COVID-19 outbreaks that occurred in tropical countries shows the existence of other factors that influence the spread of COVID-19 in addition to temperature, humidity, and climate. One important factor is the high mobility and social interaction in modern humans. Some studies recommend that if population mobility and social interaction can be truly limited, accompanied by adequate public health interventions, it will be able to break the chain of COVID-19 distribution, especially in tropical countries.

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  1. Bicara soal Corona tak akan ada habisnya. Ya? Berdoa aja semoga Corona cepat sirna dan bisa beraktivitas seperti sedia kala. Amin. Oh ya dok maaf mahu tanya sedikit nih, kalau saya konsultasi sama dokter lewat email ada yang oto marah tidak ? Terima kasih.

    1. Amin...semoga pageblug ini segera berakhir.
      Oalah mbak, konsultasi kok marah. mungkin bisa menimbulkan amraha kalaau menggunkan bahasa yang berbeda dan tidak saling mengerti, njenengan pakai bahasa India, saya pakai bahasa Thailand. hehhehehe.

      Monggo silakan konsultasi, formatnya Identitas (sex & age) + keluhan.

  2. Format sex & age maksudnya apa? Oh ya sekalian saya mahu tanya ini blognya kok tidak ada foto profil kenapa ya ? Binggung saya jadi mahu menghubungi Anda mas.

    1. Maksudnya cukup sebutkan identitas pasien (yang punya keluhan) dengan Sex (jenis kelamin) dan Age (umur). Tidak perlu nama.

      Contoh: pasien perempuan/laki usia 13th, keluhan nyeri kepala seminggu dengan mual muntah.

      Blog ini tanpa photo author sebab formatnya majalah, bukan blog diary personal.