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Why Coronavirus is more likely to “spread” than the flu

For a spike-shaped sphere only 120 nanometers wide, the coronavirus can be a remarkably cosmopolitan traveler.

If spoken from the nose or mouth, it can be fired through a room and sprayed on surfaces; can walk in poorly ventilated rooms and stay in the air for hours. In its most fearless form, the virus can spread from one individual to dozens of others, perhaps even a hundred or more at a time, spreading through packed crowds in what is called an oversupply event.

Similar scenarios, which have been traced to call centers, meat processing facilities, weddings and more, have helped drive the pandemic, which in almost eight months has reached almost every corner of the globe. Yet, while some people seem particularly prone to spreading the coronavirus, others barely transmit it.

“There’s a small percentage of people who seem to infect a lot of people,” said Dr. Joshua Schiffer, a physician and mathematical modeling expert who studies infectious diseases at the Fred Hutchinson Cancer Research Center in Seattle. The prognosis varies depending on the population, but they consistently show a striking distortion: Between 10 and 20 percent of coronavirus cases can plant 80 percent of new infections. Other respiratory diseases, such as influenza, are far more egalitarian in their spread.

Thinking about what drives coronavirus hyperprevention events can be key to stopping them and speeding up the end of a pandemic. “It’s a million-dollar issue,” said Ayesha Mahmoud, who studies the dynamics of infectious diseases at the University of California, Berkeley.

In a document posted Friday on the medRxiv website, which has not yet been peer reviewed, Dr. Schiffer and colleagues say coronavirus oversupply is likely to occur at a crossroads where bad deadlines and bad mood: a person who has reached the point of their infection when they shed large amounts of the virus and do so in an environment where there are many other people around to catch it.

According to a model built by Dr. Schiffer’s team, the most risky window for such transmission can be extremely short – a period of one to two days a week or more after a person is infected, when coronavirus levels are highest.

The virus can still spreads outside this window and people outside it should not give up measures such as wearing masks and physical distancing, Dr. Schiffer said. But the longer the infection drags on, the less likely a person is to become infected – an idea that can help experts advise when to end self-isolation or how to allocate resources to those most in need, Dr. Mahmoud said. who was not participating in the study.

However, catching and detaining a person is the most contagious is another matter. Some people affected by the coronavirus begin to feel unwell within a few days, while others take weeks, and many never experience symptoms. The length of the so-called incubation period, which covers the time between infection and the onset of symptoms, can be so different that some people who catch the virus become ill before the person who gave it to them. This rarely happens with the flu, which reliably awakens a number of symptoms within a few days of infection.

If the coronavirus peaks in the body before symptoms appear – if symptoms appear at all – this increase can be very difficult to identify without frequent and active tests. “Asymptomatic spikes in viral load appear to occur very often, which” really impairs our ability to tell when someone is infected, “Dr. Schiffer said. This in turn makes it too easy for humans to undoubtedly shed the pathogen.

“It’s really a possibility,” said Sweta Bansal, an infectious disease ecologist at Georgetown University who was not involved in the study. “These processes really come together when you’re not only infected, but you don’t know you’re infected because you don’t feel fragile.” Some of these involuntary coronavirus drivers, encouraged to go out in public, can lead to over-targeting. an event that sends the pathogen flaming through a new population.

This fusion of factors – a person in the wrong place at the wrong point of their infection – creates a scene for “transmission of an explosion,” says Dr. Bansal.

The team’s model also pointed to another important variable: the remarkable resistance of the coronavirus when it is at altitude.

The growing body of evidence now suggests that the coronavirus can be transmitted through the air in overcrowded, poorly ventilated indoor areas, where it can meet many people at once. The virus also travels in larger, heavier droplets, but they quickly fall to the ground after being expelled from the airways and do not have the same range or longevity as their smaller counterparts. Dr Schiffer said he thought the coronavirus could be more susceptible to overdose than flu viruses because it was better kept in infectious clouds that could carry pathogens over relatively long distances.

“It’s a spatial phenomenon,” he said. “People away from the transmitter may be more likely to be infected.”

Since the beginning of the pandemic, many comparisons have been made between Covid-19 and influenza, both of which are diseases caused by viruses that attack the airways. But there are many differences, and in many ways the coronavirus is more deplorable. “This study adds another layer to how it’s different from the flu,” said Olivia Prosper, a researcher at the University of Tennessee, Knoxville, who uses mathematical models to study infectious diseases but did not participate in the study. “It’s not just about how much it hurts, but also his ability to transmit.”

In addition, some people may be predisposed to being more generous transmitters of the coronavirus, although the details are “still a mystery,” Dr. Schiffer said.

But when an over-representative event occurs, it probably has more to do with the circumstances than with a person’s biology, Dr. Schiffer said. Even someone who carries a lot of the coronavirus can interfere with mass transmission by avoiding large groups, thus depriving the tube germ of travel.

“The over-presenting event is a function of what someone’s viral load is and if they are in a crowded space,” he said. “If these are the two levers, you can control the folding bit.”

Both Dr. Mahmoud and Dr. Prosper noted that not everyone has the means to practice physical distancing. Some people work in the most important jobs, for example in a packaged environment, and are left more vulnerable to the consequences of events, which are over-presentation.

This makes it even more important for those who may be involved in control measures such as wearing masks and physical distancing to remain vigilant about their behavior, Dr Mahmoud said.

“Here’s what we need to do,” she said. “Not only to protect ourselves, but also to protect others.”

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