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Study claims virus thrives in temperate climate band across globe

A study published […] suggested that COVID-19 thrives in cooler, drier weather, the latest volley in an ongoing scientific debate over whether the coronavirus is affected by seasonal changes.

The analysis, published by a team out of the University of Maryland, found that hard-hit cities around the globe were within a band between 30 and 50 degrees North, while 42 other cities that seemed to avoid the worst of the pandemic were to the north or south of them.

“The distribution of substantial community outbreaks of COVID-19 along restricted latitude, temperature, and humidity measurements was consistent with the behavior of a seasonal respiratory virus,” the authors wrote in the study, published online by the Journal of the America Medical Association.

The eight cities examined within the band were Wuhan, China; Tokyo, Japan; Daegu, South Korea; Qom, Iran; Milan, Italy; Paris, France; Seattle, Washington; and Madrid, Spain. All of them had temperatures between 41 to 51 degrees Fahrenheit and relative humidity between 44 and 84 percent when the virus was spreading most rapidly.

“We think the SARS-CoV-2 virus has a more difficult time spreading in conditions with higher temperature and humidity,” study co-author Dr. Mohammad Sajadi told UPI.

He added that researchers could use climate modeling to predict where the virus might break out next, but cautioned that more work needed to be done.

Some experts have suggested that hotter temperatures can affect the spread of the virus, though others say the climate is not a major factor. In Israel, Prime Minister Benjamin Netanyahu has insisted that heat does not affect the virus.

The authors noted in the study that coronaviruses that cause the common cold in humans “have been shown to display strong winter seasonality between December and April and are undetectable in summer months in temperate regions of the northern hemisphere.”

Maps produced by the research team showed a green band of moderate weather across the northern hemisphere that forms a sort of Goldilocks Zone for the virus, and which all eight cities fell into. Israel is just to the south of the zone.

It claimed that cities near virus centers but outside the temperate zone appeared to have fared better than those within it, though the study only includes data up to March 10. Among the cities listed as not having major outbreaks is Jerusalem, though Israel’s worst-hit city saw most of its infections only starting in late March and April.

The model conforms with major outbreaks in several cities in March and April based on the climate data, including London, Berlin, New York and Beijing.

Source: TOI Staff


Discussion on Temperature, Humidity, and Latitude Analysis to Estimate Potential Spread and Seasonality of Coronavirus Disease 2019 (COVID-19)

The distribution of the substantial community outbreaks of COVID-19 along restricted latitude, temperature, and humidity measurements were consistent with the behavior of a seasonal respiratory virus.

The association between temperature and humidity in the cities affected by COVID-19 deserves special attention.

There is a similarity in the measures of mean temperature (ie, 5-11 °C) and RH (ie, 44%-84%) in the affected cities and known laboratory conditions that are conducive to coronavirus survival (4 °C and 20%-80% RH).[…]

In the time we have written up these results, new centers of substantial community outbreaks include parts of Germany and England, all of which had seen mean temperatures between 5 and 11 °C in January and February 2020 and were included in either the January to February 2020 map […] or the March to April risk map […].

Temperature and humidity are known factors in SARS-CoV, MERS-CoV, and influenza survival.[…] Furthermore, new outbreaks occurred during prolonged periods at these temperatures, perhaps pointing to increased risk of outbreaks with prolonged conditions in this range.

Besides potentially prolonging half-life and viability of the virus, other potential mechanisms associated with cold temperature and low humidity include stabilization of the droplet, enhanced propagation in nasal mucosa, and impaired localized innate immunity, as has been demonstrated with other respiratory viruses.[…] It is important to note that even colder areas in the more northern latitudes have been relatively free of COVID-19, pointing to a potential minimum range for temperature, which could be because of avoidance of freeze-thaw cycles that could affect virus viability or other factors (given that at least 1 human coronavirus tested is freeze-thaw resistant).

Human coronaviruses (HCoV 229E, HCoV HKU1, HCoV NL63, and HCoV OC43), which usually cause common cold symptoms, have been shown to display strong winter seasonality between December and April and are undetectable in summer months in temperate regions of the northern hemisphere.[…] Some studies have shown that the alphacoronavirus HCoV 229E peaks in the fall, while HCoV OC43 (a betacoronavirus in the same genera as SARS-CoV-2) has a winter predominance.[…] Although it would be even more difficult to make a long-term estimation at this stage, it is possible that COVID-19 will diminish considerably in affected areas (above 30° N) in the coming months and into the summer. However, given that SARS-CoV-2 is only recently introduced to humans, there is presumably no preexisting immunity. In such cases, whether the 2009 H1N1 influenza pandemic or the first whooping cough pandemics documented in Persia and France in the 1400s and 1500s, the initial epidemic acted unpredictably, so in addition to their recognizable seasonal peak, they had additional peaks outside their later seasonal patterns.

The spread of the SARS-CoV-2 virus in the upcoming years could follow different patterns; it could prevail at low levels or cause several seasonal peaks in tropical regions like influenza,[…] cause outbreaks in the southern hemisphere at the same time, and begin to rise again in late fall and winter in temperate regions in the upcoming year. Another possibility is that, combined with intensive public health efforts, it will not be able to sustain itself in the summer in the tropics and southern hemisphere and disappear, just as SARS-CoV did in 2003; however, the ever-increasing number of cases worldwide make this increasingly less likely. MERS-CoV has been pointed to as a betacoronavirus that can spread in all seasons. However, it should be remembered that most cases of MERS-CoV were in the Arabian Peninsula and that influenza infection there does not follow the same pattern as in more temperate climates.[…] In the upcoming summer months in the northern hemisphere, surveillance efforts for SARS-CoV-2 in currently affected areas will be important to determine whether there is a viral reservoir (eg, prolonged stool shedding). Similarly, surveillance efforts in the tropics as well as in New Zealand, Australia, South Africa, Argentina, and Chile between the months of June and September may be of value in determining its establishment in the human population.

An avenue for further research involves the use of integrated or coupled epidemiological-earth-human systems models, which can incorporate climate and weather processes and variables (eg, dynamics of temperature, humidity) and their spatiotemporal changes as well as simulate scenarios of human interactions (eg, travel, transmission due to population density). Such models can assimilate data currently being collected to accelerate the improvements of model estimations on short time scales (ie, daily to seasonally). This approach would allow researchers to explore questions such as which population centers are most at risk and for how long; where to intensify large-scale surveillance and tighten control measures to prevent spreading; how to better understand limiting factors for virus spreading in the southern hemisphere; and how to make estimations for the 2021 to 2022 virus season. A better understanding of the cause of seasonality for coronaviruses and other respiratory viruses would undoubtedly aid in better treatments and/or prevention and be useful in determining which areas need heightened surveillance.


This study has limitations. The reported data for number of cases and mortality are invariably different in different countries, owing to differences in availability of testing, the sensitivity and specificity of each test, and reporting. Other potential factors that influence transmission (eg, other climate factors, public health interventions, travel, population density, air pollution, population demographic characteristics, viral factors) were not included in this study.


In this study, the distribution of substantial community outbreaks along restricted latitude, temperature, and humidity measurements were consistent with the behavior of a seasonal respiratory virus. Additionally, we have proposed a simplified model that shows a zone that may be at increased risk for COVID-19 spread. Using weather modeling, it may be possible to estimate the regions most likely to be at higher risk of substantial community spread of COVID-19 in the upcoming weeks and months, allowing for a concentration of public health efforts on surveillance and containment.


Daylight May Drive Seasonal Variation in SARS-CoV-2 Infectivity

  • Andy Goren, MD | Clinical Hospital Center Sestre Milosrdnice Zagreb, Croatia

SARS-CoV-2 infectivity is dependent on proteolysis of its spike protein by the TMPRSS2 enzyme expressed on the surface of type II pneumocytes (…).

In humans, the only known promoter of the TMPRSS2 gene is an androgen response element; therefore, androgen receptor expression is likely to determine COVID-19 disease severity (…).

In support of the androgen driven COVID-19 hypothesis, a recent study from Italy (…) demonstrated a significant protective effect of androgen depravation therapy in COVID-19 prostate cancer patients OR 4.05 (95% CI: 1.55-10.59). Androgen receptor expression is mediated by the period circadian protein homolog 1 (Per1). Per1 overexpression inhibits the transactivation of the androgen receptor(…). Per1 expression follows a circadian cycle determined by the length of the daylight. Rats exposed to a longer photoperiod (16 hours light and 8 hours darkness) exhibit higher expression of Per1 compared to rats exposed to a shorter photoperiod (8 hours light and 16 hours darkness) (…).

In conclusion, during the fall and the winter months when daylight is short, TMPRSS2 expression is likely to be increased which may lead to increased SARS-CoV-2 infectivity.

Header: A map showing the temperate zone, highlighted in red, where the virus had climate conditions to thrive, according to a study published June 11, 2020. (CC-BY Sajadi MM et al. JAMA Network Open)