How will the COVID-19 pandemic end?
Shops on Main Street in downtown Ventura will reopen after the COVID-19 pandemic closes. Scientists say it is too early to predict how the outbreak will end.
To prevent a dangerous new virus from finding its way with humanity, you can take a side from the Chinese warrior king Sun Tzu and think like the enemy.
Imagine you are a coronavirus in a form that humans have never seen before. Your goal is simple, but very ambitious: invading and kidnapping the cells of a new host and multiplying until your spawn is established in at least one other new host.
Repeat until no more people can be infected.
Since its emergence in the home of Sun Tzu, the corona virus, known to scientists as SARS-CoV-2, has done its job with vigor and success. It easily crossed national borders, infected more than 9 million people around the world, and killed at least 470,000 people in about seven months. The approximately 7.7 billion people who have so far evaded an infection seem to be closely targeted.
But humanity has a few tricks of its own.
In seizures and beginnings, public health officials have brought their citizens together to avoid the kind of gatherings that offer a virus-rich spread. Scientists have looked into the genome of the corona virus to unravel mysteries of where it came from, how it evolved, and what it takes to thwart it.
Now it's a race to see which side wins.
Viruses are not as intelligent as humans, but they are much more patient, said Harvard University epidemiologist William Hanage. And the track record of this virus is not a good sign of a strategy to ignore it, hoping that it burns itself out, he added.
"That would wait for the virus to help us," Hanage said. "That's not a good idea."
Bernie Erwig, 84, is rolled out of a nursing home in Riverside after a test showed he had COVID-19. (Gina Ferazzi / Los Angeles Times)
The survival necessities make a successful virus an unpredictable guest - cruel to some, friendlier to others, and able to develop new strategies as its pool of potential targets diminishes.
"There is no reward that a virus line is easy for its host," said Frederick M. Cohan, evolutionary biologist at Wesleyan University.
It must not kill him immediately, as many early forms of the Ebola virus did to their victims. Such outbreaks are designed to hiss.
But a successful virus can leave its victim exhausted, Cohan said: As long as he has managed to make him sick enough to drag others to his bed, where they are exposed to body fluids or breath droplets, another victim will live infect.
At least initially, it doesn't have to be picky about its victims. It can spare the young and healthy and chase the weak and infirm first, as the corona virus seems to do.
However, experts believe that a virus that stands the test of time will wane as its potential hosts dwindle and public health precautions are taken.
In order to spread further in such circumstances, a virus must leave many of its victims in a state in which they can move. It could attack younger hosts who may not get so sick but are better spreaders. It could be transmitted by people who don't even notice they're infected. The corona virus has done all of this with great effect.
Many viruses have to deal with an inherently tough struggle: on their way through a population, the victims who infect them recover or recover. And those who are recovering will usually show up with some immunity.
After romping around in a targeted environment for the first time, a novel virus detects that its potential victims have shrunk. People at risk of infection are no longer so close together. This is a problem for a respiratory virus like SARS-CoV-2 that can only spread if potential hosts are grouped together. (Many other viruses spread in the water or in the bellies of mosquitoes, fleas and birds, so that social distance does not counteract them either.)
An overly aggressive virus can become a victim of its own success and infect so many people so quickly that it can do what epidemiologists call "herd immunity". In this scenario, the remaining uninfected targets are simply too far apart for the pathogen to spread further.
Of the seven coronaviruses known to make people sick, at least four have found a way to bypass herd immunity and maintain it in the long term. These viruses, which cause all variations of the common cold, leave most victims with immunity that wears off in just over a year. The pool of people who are vulnerable to becoming hosts is constantly renewed as the immune system of infected people "forgets" the virus that previously made them sick.
No one knows if the coronavirus that causes COVID-19 shares this trait. However, a large number of studies indicate that immunity is either weak or temporary in many infected people.
With regard to evolutionary biology, there is another way to maintain an inexhaustible supply of potential hosts: if a virus can mutate quickly enough and in a certain way, it can escape detection by an immune system that it has previously encountered.
The new corona virus is constantly mutating because its genetic instructions are encoded in RNA. Compared to a DNA virus like the one that causes measles, an RNA virus is simpler and less likely to correct the errors that occur with each replication.
Most mutations are tiny substitutions of nucleotides that have no effect on the behavior of the virus. But over time, these accumulated errors can change the way it looks for an immune system or how it interacts with its environment or its hosts. And every now and then a mutation (or a series of mutations) gives the virus a sudden advantage.
Members of the Red Cross remove patients from a house during the 1918 influenza pandemic. By the end of the third and final wave, an estimated one third of the world's population was infected.
The 1918 influenza pandemic began after an accidental mutation charged the reproductive machinery. Patients became ill more quickly, and since their immune systems were fully mobilized, they released more viruses when they coughed and sneezed - and infected more people around them.
Scientists have seen the genome of the new corona virus change, causing some to claim that more virulent and communicable strains are in circulation. These claims have been the subject of heated debate. However, SARS-CoV-2's talent for reshaping has transformed it from a virus that thrived in bats and possibly pangolines to a virus that can infect humans.
Additional mutations could bring new challenges for people - or new opportunities. If we're lucky, a mutation could make the virus less contagious or less deadly.
But humans have also learned a few tricks to counter such viral strategies.
Long before our ancestors understood that germs spread disease, they realized that creating distance between people meant that fewer of them became sick. During an outbreak, those from cities fled to their rural homes with funds. Those who stayed avoided the market place. Public spectacles have been canceled. It was the beginning of the public health strategy that we now refer to as social distancing.
The corona virus needs people who are close together and touch common surfaces to spread from person to person. Social distancing changes the environment to mimic the effects of herd immunity.
The other way to deny a host a virus is to put more people in the “recovered category” - a status that more than 4.6 million people now have.
You do this by letting the pandemic run, provided immunity continues. Or you can make a vaccine.
It would be a catastrophe on the order of catastrophic and unimaginable if the coronavirus found its way with humanity: Harvard epidemiologist Marc Lipsitch has estimated that SARS-CoV-2 with minimal human intervention plausibly accounts for 20% to 60% of all adults would infect - between 1.5 and 4.5 billion people. Even if it weren't more lethal than seasonal flu - a very optimistic assumption - between 1.5 and 4.5 million people would die.
A widespread vaccine could ensure herd immunity, stop the virus and result in far fewer deaths. But it will take some time. Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said that parallel efforts to develop, test and manufacture many vaccines are likely to result in at least one by the end of the year.
Until then, this sly enemy has time on his side and some proven tricks to keep himself safe.
Although the coronavirus may not affect everyone on the planet, it seems to have found the support it needs to keep trying, said Columbia University virologist Angela Rasmussen. Like many flu viruses, it could mutate from year to year just enough to be new to our immune system every time it occurs. It could also change in a way that makes it more similar to the four other corona viruses that have infected humans for eons: killing few while most people are just sick enough to pass it on.
From a virus perspective, the definition of success is "getting a cold," said Cohan. Together with many microbiologists, he suspects that this virus has what it takes to distance itself. People could outsmart it with a good vaccine, although the immunity it offers may be temporary. And many who are not afraid of the virus would probably skip it anyway.
He hopes his suspicions are wrong. But a career in studying disease-causing microbes was a chastisement, he said.
"We are not smart enough to know what they will do," said Cohan. "And if we think we know, they'll just surprise us."
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