Will the spread of the novel coronavirus weaken because of high temperature?

Midsummer in the northern hemisphere is approaching. There is still a question that remains to be resolved: whether the arrival of high-temperature weather will help reduce the spread of the novel coronavirus (SARS-CoV-2). Other members of the same family as the novel coronavirus, such as SARS and other coronaviruses, mostly show a certain seasonal pattern-in the high temperature and high humidity summer, the virus activity will be reduced. SARS quietly retired before the advent of midsummer. However, the bad news is now waiting.

On May 18, 2020, a research paper published by the Princeton University researchers in the famous journal "Science" stated that the northern hemisphere is approaching summer, but the increased temperature is unlikely to significantly inhibit the spread of the new coronary pneumonia epidemic. The researchers pointed out that because there are still highly susceptible people in the community, it is still impossible to figure out whether the seasonal climate and geographical changes will greatly change the trajectory of the new crown epidemic. The world is still in a period of pandemic epidemic. At this time, virus transmission generally does not follow the usual pattern. At present, the novel coronavirus has spread in the community, and there are still a large number of susceptible people, so it is more effective public health measures to contain the virus. Even if the Northern Hemisphere has begun to enter the summer, the spread of the novel coronavirus continues. How climatic factors affect the spread of the novel coronavirus still needs more relevant evidence to study, so no one can really determine whether this virus will make a comeback in autumn.

Virus and temperature

It is generally recognized that coronavirus is incompatible with high temperature and is more sensitive to heat. Studies have shown that the novel coronavirus is very stable at 4°C. As the ambient temperature increases to 70°C, the novel coronavirus loses its activity after 5 minutes. The structure of the coronavirus is complicated. Its outer side is covered with an envelope, and the envelope is covered with obvious rod-shaped protruding proteins. Because it looks like a medieval European imperial crown, it is named "coronavirus". The envelope not only maintains the structural integrity of the virus, but also participates in the virus' invasion of the host cell, helping the virus to recognize and bind to the receptors located on the host cell membrane. Once the envelope is combined with the cell membrane of the host cell, the core of the virus is the DNA, RNA, and protein material inside the virus that enters the host cell, and the infection is complete. On the cell membrane, there is a substance called transmembrane protein that is responsible for the work of a community guard. He has a pass list on his hand, and only the substances on the list can enter and exit the community gate. There is a spike on the novel coronavirus, this time it is actually a protein called spike glycoprotein. They can use this protein as a key to open a lock called ACE2 protein, and after opening the lock, it can enter the cell body in a grand manner.

The envelope makes the virus more adaptable to colder environments. Under colder conditions, the outer coating will harden into a rubber-like shape, just like in cooked meat, the fat will harden as it cools, protecting the virus from persisting longer. But in the environment with higher temperature, the protection against viruses is reduced. Therefore, most enveloped viruses often exhibit strong seasonality. SARS coronavirus (SARS-CoV) can survive for four days at 37℃. Heating at 56°C for 90 minutes and 75°C for 30 minutes can deactivate the virus. Another coronavirus, HCoV-229E, loses its infectivity at 56°C for 10 minutes or 37°C for several hours. The high temperature in summer is often accompanied by strong ultraviolet rays. Ultraviolet rays decompose nucleic acids, which destroys the genetic material of the virus, making it impossible to continue to replicate and quickly reduce. This method, which can effectively kill bacteria and viruses, is very common in hospitals and disinfects various equipment. Returning to the novel coronavirus, if the high temperature can prevent the virus from replicating and infecting, then the spread of the novel coronavirus should occur at different times around the world. The reality is not satisfactory. Even if the Northern Hemisphere has begun to enter the summer, the spread of the novel coronavirus continues.

Previously, researchers at Harvard Medical School analyzed the spread of this virus in Asia. The results showed that the novel coronavirus that caused the pandemic was not as sensitive to weather as many people expected. Harvard researchers concluded that in the cold and dry provinces of China, such as Jilin and Heilongjiang, the growth rate of cases is similar to that of tropical regions such as Guangxi; the changes in temperature and humidity in spring and summer will not have a significant impact on the growth of new coronary pneumonia.

Novel coronavirus and temperature

With the northern and southern hemispheres, the seasons change. Researchers are trying to find out the relationship between the novel coronavirus and the climate through more research. Marc Lipsitch, an epidemiologist at Harvard University, mentioned in an interview with the media that if the novel coronavirus is similar to a typical flu virus, its spread in the southern hemisphere may deteriorate as the seasons change, The spread in the northern hemisphere may have eased. On April 20th, Italian researchers published a paper on the medical journal preprint platform medRxiv. The spread of the novel coronavirus peaked in the temperate region of the northern hemisphere, with an average temperature of about 5°C and a moisture content of 4-6 g/ m3, but lower in warmer/humid and colder/dry areas. This shows that environmental factors, including seasonal climate changes, can have a strong impact on the temporal and spatial patterns of outbreaks of infectious diseases. But this does not resolve the relationship between the new global pneumonia epidemic and the climate, and whether the climate can contain the epidemic.

On May 6, researchers at the London School of Hygiene and Tropical Medicine (LSHTM) published in a medical journal that the spread of the novel coronavirus worldwide indicates that the season cannot be considered a key regulator of the spread of the novel coronavirus. Although climate warming may slightly reduce the spread of the virus, there is no evidence that climate warming will reduce the effectiveness of the spread of the novel coronavirus, so that little additional intervention is needed to curb its spread. In order to better understand the novel coronavirus, scientists are studying other human coronaviruses similar to it, such as SARS virus and MERS virus. The SARS virus shares nearly 90% of DNA with the new crown virus. The SARS outbreak began in November 2002 and continued into July of the following year. In the meantime, the spread of the SARS virus has been quickly contained by a series of public health measures. It is difficult to analyze whether early intervention played a role, or the virus showed a natural decay as the weather warmed. Another brother of the new coronavirus, the MERS virus, started in September 2012 in Saudi Arabia, where temperatures are generally higher. Unlike SARS, it has never been completely contained and new cases are still sporadic.

Even if there is a certain correlation between the novel coronavirus and the temperature, it is now a global pandemic of the new coronary pneumonia, whether summer or not, is no longer a key factor. On May 18, a study by researchers at Princeton University in the United States showed that the increased summer temperature in the northern hemisphere is unlikely to significantly inhibit the spread of the new coronary pneumonia epidemic. Although the climate may regulate the size and time of the novel coronavirus outbreak in specific locations, whether there are a large number of susceptible people is still a more fundamental driving factor for epidemic invasion.

China experienced the first wave of the new crown epidemic in early 2020. The outbreak of the epidemic quickly cut off the local transmission. The infection rate of the population is low, the majority of people are not immune, and the proportion of susceptible people is large. Yang Weizhong, a member of the Chinese Preventive Medicine Association, once pointed out that once a new source of infection is not controlled in time, it is easy to spread among the crowd and cause the epidemic to rebound. This means that whether the arrival of summer can curb the spread of novel coronavirus to a certain extent is still questionable. Researchers at the London School of Hygiene and Tropical Medicine said that further research on the impact of climate change, air pollution, and other external factors on the spread of new coronary pneumonia requires consideration of population migration from areas with high incidence rates, population susceptibility, and monitoring of respiratory infections.

At present, policymakers must focus on reducing interpersonal contact within the community, and any new coronary risk prediction based on climate information should be interpreted with caution. The head of the WHO emergency project, Michael Ryan, also pointed out that there has not been a second wave of the epidemic, and it is now in the first wave of the epidemic. According to data from Central and South America, Africa, and South Asia, the epidemic is on the rise. Countries in Europe, North America, and Southeast Asia should continue to adopt comprehensive strategies such as public health and social measures, and monitoring measures to ensure that the epidemic situation continues to be on the declining track, and there will not be a second peak immediately. Now, the climate is not as important as expected.