In the four months to December 2019, the new corona outbreak has engulfed nearly 190 countries and regions around the world. When will the still-unknown pandemic end? Based on previous experience in epidemics such as SARS (Severe Acute Respiratory Syndrome), there is also hope that the summer will be more “efficient” in smothering the virus.
On March 19, local time, two mites from the Massachusetts Institute of Technology (MIT) published a paper, “Will Corona CoronaVirus By Summer?” on the preprint platform SSRN, and the two men were Qasim of the McGovern Brain Institute. Bukhari and Yusuf Jameel of the Department of Civil and Environmental Engineering. They said that although the flu virus has been shown to be affected by the weather, it is not clear whether COVID-19 has been affected in a similar way. For the study, they focused on the effects of weather on the spread of the new coronavirus.
Their results show that 90% of the transmission of the new coronavirus has occurred in the range of a certain temperature (3C-17C) and absolute humidity (4g/m3-9g/m3). The total number of cases in countries with average temperatures above 18 degrees C and absolute humidity (AH) greater than 9g/m3 between January and March is actually less than 6% of the global total.
Their analysis shows that overall, the chances of reducing the spread of the virus due to environmental factors will be limited in most of northern Europe and North America (the United States and Canada). On the other hand, Asian countries, especially those experiencing monsoons, will have absolute humidity greater than 10g/m3 between June and September, and the spread of the virus will be somewhat alleviated.
Such research is not an isolated one. Earlier, on March 9, researchers at the Human Virus Institute at the University of Maryland School of Medicine and the Global Virus Network (GVN) Center of Excellence published a study in SSRN, which made a similar point that so far, outbreaks caused by the new coronavirus have spread mainly along narrow, east-west, roughly along the 30-50th parallel. Corridors, this area has a similar temperature: 5C-11C, similar relative humidity (RH): 47%-79%.
Both the scientific community and the public’s expectations of summer are more or less partly based. SARS 17 years ago appeared in the winter of the first year, but quietly disappeared the following summer, and even seemed completely extinct. At that time, the global response was far less rapid and rigorous than the new corona outbreak.
In addition to SARS-CoV, the new coronavirus can cause serious diseases of the virus, other perennial influenza is showing significant seasonality, in temperate regions, the northern hemisphere from November to March, the southern hemisphere from May to September is generally influenza season. Over the past half century of discussion and research, it has come to a well-established view that low-temperature, low-humid air environments are an important factor in the spread of winter flu.
However, the scientific community’s research on coronavirus and climate correlation still needs to be in-depth and clear. In this study, Bukhari stressed that the relationship between the number of new coronavirus cases and temperature and absolute humidity is close in terms of the current spread of the virus. However, the underlying reasons behind this relationship remain unclear, or even rule-out, without any impact.
They stressed that appropriate quarantine measures should be taken even in warmer and humid areas. But at the same time, the relationship between temperature and humidity and new coronavirus cases should be closely monitored, and if there is a strong environmental dependence on the transmission of the new coronavirus, this relationship should be used to optimize the outbreak mitigation strategy.
Significant differences in the rate of growth of new crown cases vary from country to country
The analysis from Bukhari et al.’s study provides a direct comparison of neo-coronavirus transmission and local environmental conditions, with significant differences in the rate of growth of new coronary cases between different countries and significant differences between states in the United States.
Growth curve for new crown cases in different countries (as of 19 March 2020). Figures show the total number of cases for the period from 23 February to 19 March. The growth curves vary significantly between regions and states.
Growth curve for new crown cases in U.S. states (as of March 19, 2020). The figures show the total number of cases for the period from 9 March to 19 March. The growth curves of different regions and states are significantly different.
For now, Italy, Iran and South Korea are growing at a higher rate, showing similar weather patterns to those in Wuhan, China, where the outbreak occurred, where their average temperatures were 3-10 degrees Celsius between February and March. In contrast, warmer and humid countries such as Singapore, Malaysia, Thailand and other Southeast Asian countries have slower growth rates.
The new coronary outbreak affects the region’s temperature and absolute humidity over time. Areas with high temperature and absolute humidity (Singapore and Thailand) reported fewer new coronary cases. Hubei, the center of the epidemic, is represented by a red dotted line. The temperature and absolute humidity range sits in light blue for most new coronal cases (?gt;90%) with temperatures between 3C and 17C and absolute humidity between 4g/m3-8g/m3.
Within the United States, the outbreak also shows a North-South difference. The colder northern states have much higher growth rates than the warmer southern states. Although the number of cases in Florida increased dramatically between March 17 and March 20 due to retrospective sample analysis, the spread of the new coronavirus in Florida, Texas and Arizona was limited.
In California, which straddles the climate belt, Northern California has twice as many cases as Southern California.
It is worth noting that oregon and Louisiana are two outliers in the United States. Oregon, though located between California and Washington state, has fewer than 100 cases. Similarly, Louisiana, though relatively warm and humid, has only about 500 cases.
Bukhari et al. note that no country in Asia, the Middle East and South America has implemented quarantine measures as severe as in china, Europe and the United States, but their overall growth rate remains low.
This suggests that, in addition to mobility and isolation factors, other factors may also play an important role in slowing the spread of the virus.
Since climate appears to be one of the main differences between high and low growth countries, Bukhari et al. believe that the role of weather in coronavirus transmission should be explored in depth, assuming that “the effect sits on the condition that this is present”.
So far: much smaller cases in areas with temperatures above 17C and absolute humidity greater than 9g/m3
Analysis by Bukhari et al. shows that from 22 January 2020 to 19 March 2020, the average temperature was between 4c and 10C and the absolute humidity was between 3g/m3-9g/m3, with the highest number of new cases per 10 days. In addition to new cases, the total number of cases in areas with temperatures above 11 degrees C and below 0 degrees C is less than 5%, while the total number of cases in areas with absolute humidity greater than 9g/m3 is less than 10%.
The number of new crown cases worldwide as temperature and absolute humidity change. The figure shows new coronary cases reported every 10 days at different temperatures and absolute humidity. The temperature and absolute humidity range sits in light blue for most new coronal cases (?gt;90%) with temperatures between 3C and 17C and absolute humidity between 4g/m3-8g/m3.
The first thing to do here is to explain absolute humidity. The humidity generally referred to is the relative humidity (RH), which is the relative ratio of absolute humidity to the saturated absolute humidity at that temperature. Absolute humidity (AH) is the actual moisture content in the unit air.
A recent article by the Beijing Association of Science and Technology points out that at certain temperatures, increasing the relative humidity also increases the absolute humidity. Until the relative humidity reaches 100%, the water vapor will condensate out, at which point the absolute humidity can not continue to increase, that is, to reach the saturation absolute humidity at that temperature. At this point, the temperature needs to be increased, so that the air can accommodate water vapor capacity increased, in order to continue to increase absolute humidity.
Although relative humidity is more convenient to measure, researchers generally associate absolute humidity as an indicator of the virus’s propagation characteristics, given that absolute humidity can more directly measure the amount of water vapor in the air and that it also implies a direct effect on the virus.
For the Wuhan area on the edge of the river, the Beijing Association of Science and Technology’s article also briefly mentioned, “Winter temperature is low, so although the relative humidity is large, but the absolute humidity is not large.” Wait until summer to see. “
Between 11 March and 19 March, Bukhari et al. observed that, although the number of cases in the Middle East, South America, Asia and Africa (warm regions) had increased dramatically, they were still less than 1/10 of the region between 8c and 12C. They believe that this growth of the virus in warmer regions is unlikely. Data to date clearly indicate that the number of cases in areas where temperatures above 17 degrees C and absolute humidity greater than 9g/m3 are much lower.
Based on current data, the researchers hypothesize that the virus may spread more slowly in warm and humid conditions. “Of course, as an objection to this hypothesis, we can also assume that there is a high level of human mobility between China and Europe, as well as between China and the United States, and therefore a high number of cases in these regions,” they wrote in the paper. “
But for these reasons, Bukhari et al. believe they have yet to be explored. For example, the high level of population mobility between China and South-East Asia is inexplicable.
There may also be counterarguments that Hong Kong, Singapore and Taiwan have built a strong infrastructure to respond to the SARS outbreak, which may help curb the spread of the virus. However, Bukhari et al. argue that such complex infrastructure does not exist in Malaysia, Thailand, the Philippines and Cambodia.
As a result, the researchers argue that it is not possible to explain the lower growth rates in all of Southeast Asia by China’s low population mobility or strong health infrastructure.
Similarly, China has important business ties with Africa and Latin America, where there are no reported large numbers of cases. Most of these countries lack good health care facilities and may not be adequately tested to determine the actual spread of the neo-coronavirus.
By observing the spread of the new coronavirus in Saudi Arabia and the United Arab Emirates, the researchers also obtained further evidence to support their hypothesis. They mentioned that thousands of pilgrims from all over the world visit Saudi Arabia, and that the UAE is an important international hub, visited by millions of tourists and businessmen from all over the world every year. Moreover, as of March 20, 2020, the UAE has the highest number of coronavirus tests per capita in the world.
Although the two countries have adopted stringent quarantine measures in the past few days, the number of cases suggests that the spread of the virus was limited even before quarantine measures.
Why have recent peaks of new crown cases occurred in warmer and humid areas?
It was noted that in the past week (13 March-21 March), several countries in Asia, South America and Africa had begun to experience an increase in the number of new coronal cases. Studies have speculated that the number of new crown cases in many countries will increase exponentially, but Bukhari et al. say this speculation is incorrect.
The main reason is that some countries have only recently begun to detect new coronaviruses, and once detection is started there is bound to be a surge. They also believe that the difference between local transmission and export cases (i.e. infected elsewhere but tested in another region) should be taken into account.
It is also important to consider that, unlike the strict embargo imposed by Europe and the United States, there is still a movement between the Middle East, Africa, South America and South Asia (as of 16 March 2020).
In Pakistan and Qatar, most cases are imported from Iran. As of noon on 14 March, Malaysia had confirmed 77 cases from a single incident, namely, a religious event in Kuala Lumpur from late February to early March;
Bukhari et al. also believe that the number of cases is likely to increase significantly as governments in the Indian subcontinent step up testing.
But they believe that in these relatively warm and humid countries (India, Pakistan and Bangladesh, which together account for 22 per cent of the global population), the trajectory of the outbreak over the next month will also help to better understand the new coronavirus’s dependence on temperature and humidity.
Temperature, humidity, which environmental impact factor is more important?
From the existing epidemic transmission, the researchers believe that the number of new coronavirus cases and temperature and absolute humidity are closely related. However, the underlying reasons behind this relationship remain unclear. Similarly, the researchers did not know which environmental factors were more important, perhaps one of them, or as important as both, and certainly not to rule out the possibility that neither would affect them.
Their analysis shows that by 11 March, 90 percent of new coronavirus cases occurred in areas with temperatures below 11 degrees Celsius, suggesting that temperatures may play an important role in the spread of the virus, with higher temperatures limiting the spread of the virus.
However, between 10 March and 19 March, almost 5% of new cases occurred in areas with temperatures between 16c and 18C. This phenomenon may challenge the assumption that rising temperatures will slow the spread of the new coronavirus.
However, the slight surge in the number of cases in the 16-18 oC region above should not allow us to completely ignore the relationship between temperature and the new coronal outbreak, unless the outbreak is widespread in all temperature regions, and the link between the number of cases and air temperature will disappear in the coming months. Given that the northern hemisphere is approaching summer, they expect to see changes in the number of cases and temperatures.
Of course, even though the number of cases in areas with temperatures of 20c is relatively small, it has a limited immediate effect on the current priority outbreak areas in Europe and the northern United States, where most cities will have average temperatures below 20C between April and May.
Absolute humidity is always closely linked to the outbreak compared to temperature, with 90% of cases occurring in areas where absolute humidity is between 4 g/m3-9g/m3. Bukhari et al. mentioned that previous studies have pointed out that absolute humidity plays an important role in the spread of the virus, its role in the spread of the new coronavirus should be studied in depth.
Absolute humidity varies with temperature and relative humidity. So far, more than 90% of new coronary cases have occurred in the red zone. Less than 10 per cent of cases were reported in areas with absolute humidity greater than 10g/m3 or less than 4g/m3.
The researchers calculated theoretical absolute humidity at temperatures between -5C-40C and relative humidity (RH) between 0-100% of the theoretical. Absolute humidity is less than 9g/m3 in areas where temperatures are below 15C. When the temperature is between 15 and 25 degrees C, if the absolute humidity is less than 9g/m3, the relative humidity must be greater than 60%.
This suggests that even if the new coronavirus spreads less in areas with higher humidity, this reduction will be limited in areas above 40 degrees north latitude (including most of North America and Europe), where average temperatures and relative humidity are only above 20 degrees Celsius and 80 per cent in July and August, respectively.
Given the narrow fluctuations in absolute humidity (4g/m3-9g/m3) observed in most case environments, as well as the relationship between previous virus transmission and humidity, Bukhari et al. believe that absolute humidity may play a greater role in the spread of the new coronavirus.
Overall, Bukhari and others say their analysis suggests that the chances of reducing transmission due to environmental factors will be limited in most of northern Europe and North America (the United States and Canada). On the other hand, Asian countries, especially those experiencing monsoons, will have absolute humidity greater than 10g/m3 between June and September, and the spread of the virus will be somewhat alleviated.
Explanation based on observational speculation
Based on the current scientific understanding of the new coronavirus, many problems have not been clearly explained.
There are currently seven known human coronaviruses: four common viruses that cause mild or moderate respiratory infections, namely 229E, NL63, OC43 and KHU1, and three coronaviruses that can cause severe symptoms or even death, namely SARS-CoV, MERS-CoV and emerging new coronaviruses.
The “Public Protection Guide for pneumonia of new coronavirus infection” prepared by the CDC of China points out that coronaviruses belong to the set of viruses, coronavirus esmography, coronavirus genus, is a class of RNA viruses with cystic membranes, genomes are linear single-stranded positive chain, is a widely existing virus in nature, It is also the largest known virus with a genome (27-32kb in length).
The scientific community has previously conducted some research on coronaviruses. The above-mentioned protective guidelines mention that the human coronavirus is more sensitive to heat, the virus in 4 degrees C suitably maintain droplets for medium stability, -60 degrees C can be preserved for several years, but as the temperature increases, the resistance of the virus decreased, such as HCoV-229E at 56 degrees C for 10 minutes or 37 degrees C for a few hours even if it lost its infection.
In addition, human coronavirus is not resistant to acid, alkali, virus replication is the most suitable pH of 7.2. The human coronavirus is sensitive to organic solvents and disinfectants, and 75% ethanol, ether, chloroform, formaldehyde, chlorine-containing disinfectants, peroxyacetic acid and UV can all inactivate the virus.
Bukhari et al. analyzed the temperature dependence of the new coronavirus may be similar to SARS-Cov, which at higher temperatures is lost to the ability to survive due to the breakdown of lipid layers at higher temperatures.
Humidity dependence may be due to poor air propagation performance of the virus at higher absolute humidity, which reduces the overall indirect transmission of the new coronavirus at higher humidity levels. The decrease in the spread of neo-coronavirus in humid climates may be due to the possibility that, although high humidity increases the number of viruses deposited on the surface and also prolongs the survival of viruses in the performance droplets, the spread of the virus from direct and indirect (through air) to transmission can only be directly.
However, Bukhari et al. stress that these explanations are based on observations of other coronavirus patterns. The scientific community still urgently needs to study the correlation between coronavirus transmission and temperature and humidity under laboratory control conditions.
Emphasize: Take appropriate quarantine measures even in warmer and humid areas
Bukhari et al.’s hypothesis is based on available data and its correctness will be automatically tested in the coming weeks as new cases are reported around the world. They believe that the relationship between temperature and humidity and cases of neo-coronavirus should be closely monitored and should be used to optimize outbreak mitigation strategies if there is a strong environmental dependence on the transmission of the new coronavirus.
They also stressed that the results in no way mean that the new coronavirus will not spread in warm and humid areas, and that effective public health interventions should be undertaken around the world to effectively reduce the spread of neo-coronaviruses and protect vulnerable groups from infection.
At present, some countries have adopted a “flattening virus epidemic curve” strategy, that is, to smooth the virus epidemic. This means that these countries have prevented the outbreak from losing control by keeping the rate of new cases within the reach of a health-care system, such as isolation. If the prevalence curve is steep, the local health care system is overloaded in the short term, new patients cannot be admitted, and even serious conditions such as shortages of medical supplies occur.
Bukhari et al. point out that while appropriate isolation measures help flatten the curve, they believe that warm, humid weather in the future could slow transmission in parts of Asia. However, these reliefs appear to be limited for Europe and North America.
In addition to weather factors, there are several other factors that affect the number of affected cases in any region, including population, quality of care, medical interventions, global connectivity, etc. They believe that future work should include using these factors to predict propagation through deep learning modeling.
The study, from the University of Maryland School of Medicine, also noted that further research would be done by integrating epidemiological-human system models. The model can combine variables such as climate and weather (e.g. temperature, changes in humidity) with their temporal and temporal variations, while adding simulations of human interaction scenarios (e.g., travel, propagation caused by population density), which will greatly improve the current model.
The University of Maryland School of Medicine said at the time that while long-term predictions of the new coronavirus would be difficult at this stage, the areas currently affected by the outbreak were expected to be significantly reduced in the coming months. The team believes it is possible that the new coronavirus will continue to spread at low levels in the tropics and re-epidemic in temperate regions in late autumn, winter and the beginning of the following year. Another possibility is that with the arrival of summer, the new coronavirus will not survive in the tropics and the southern hemisphere and eventually disappear.
This means that between June and September, new coronavirus surveillance in New Zealand, Australia, South Africa, Argentina and Chile will be significant.