The Coronavirus Is Never Going Away

 

Brian L. Frank / The New York Times / NIH / The Atlantic

If there was ever a time when this coronavirus could be contained, it has probably passed. Even when a much-anticipated vaccine arrives, it is likely to only suppress but never completely eradicate the virus. We will probably be living with this virus for the rest of our lives. Back in the winter, public-health officials were more hopeful about SARS-CoV-2, the coronavirus that causes COVID-19.

SARS, a closely related coronavirus, emerged in late 2002 and infected more than 8,000 people but was snuffed out through intense isolation, contact tracing, and quarantine. The virus was gone from humans by 2004. «It’s very unlikely we’re going to be able to declare the kind of victory we did over SARS,» says Stephen Morse, an epidemiologist at Columbia University. That will depend, says Yonatan Grad, on the strength and duration of immunity against the virus.

Grad, an infectious-disease researcher at Harvard, and his colleagues have modeled a few possible trajectories. If immunity lasts only a few months, there could be a big pandemic followed by smaller outbreaks every year. If immunity lasts closer to two years, COVID-19 could peak every other year. Rather than a onetime deal, a COVID-19 vaccine, when it arrives, could require booster shots to maintain immunity over time.

Timothy Sheahan, a virologist at the University of North Carolina at Chapel Hill, wonders if, with SARS-CoV-2 so widespread across the globe, humans might be infecting new species and creating new animal reservoirs. «How do you begin to know the extent of virus spread outside of the human population and in wild and domestic animals?» he says. So far, tigers at the Bronx Zoo and minks on Dutch farms seem to have caught COVID-19 from humans and, in the case of the minks, passed the virus back to humans who work on the farm. The existence of animal reservoirs that can keep reinfecting humans is also why scientists don’t speak of «eradication» for these viruses.

The Ebola virus, for example, probably comes from bats. Even though human-to-human transmission of Ebola eventually ended in the West African epidemic in 2016, the virus was still somewhere on Earth and could still infect humans if it found the right host. Ebola can be contained through contact tracing, isolation, and a new vaccine, but it cannot be «eradicated.» No one is quite sure why SARS has never reemerged from an animal reservoir, but this coronavirus could well follow a different pattern. In the best-case scenario, a vaccine and better treatments blunt COVID-19’s severity, making it a much less dangerous and less disruptive disease.

One endgame is that SARS-CoV-2 becomes the fifth coronavirus that regularly circulates among humans. In fact, virologists have wondered whether the common-cold coronaviruses also got their start as a pandemic, before settling in as routine viruses. In 2005, biologists in Belgium studied mutations in the cold coronavirus OC43, which likely evolved from a closely related coronavirus that infects cows. Because genetic mutations accumulate at a somewhat regular rate, the researchers were able to date the spillover from cows into humans to the late 1800s.

Around this time, a highly infectious respiratory disease was killing cows, and even more curiously, in 1889, a human pandemic began killing people around the world. This is all speculative, and the possible links between the other three cold coronaviruses and past pandemics are even less clear, says Burtram Fielding, a coronavirus researcher at the University of the Western Cape. «But,» he says, «I wouldn’t be surprised.» It would also be good news, in a way, because it would suggest that COVID-19 could become less deadly over time, making that transition from pandemic to common cold. With a virus, there is a general trade-off between how contagious it is and how deadly it is.

All of this, along with immunity from vaccines, means that COVID-19 is likely to become far less disruptive down the line. The «flu» is not one virus but actually several different strains that circulate seasonally. After pandemics like 2009’s H1N1 flu, also known as swine flu, the pandemic strain does not simply disappear. Instead, it turns into a seasonal flu strain that circulates all year but peaks during the winter.

A descendent of the 2009 H1N1 pandemic strain is still the seasonal flu today. The seasonal peaks never quite reach pandemic heights because of building immunity in the population. Eventually, a new strain, against which people have no immunity, comes along and sparks a new pandemic, and then it becomes the new dominant seasonal strain. In this way, the long-term outlook for COVID-19 might offer some hope for a return to normal.

«I think this virus is with us to the future,» Ruth Karron, a vaccine researcher at Johns Hopkins, told me.

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Source: Sarah Zhang | The Atlantic