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Friday, April 19, 2024

The Pandemic Will End—but Covid-19 May Be Here to Stay

For all the chaos of vaccine distribution and appointment-making, Covid-19 vaccination in the United States is going better than it initially seemed. As of Friday, the Centers for Disease Control and Prevention’s vaccine tracker showed almost 58 million doses had been given out. Last Tuesday, President Joe Biden announced that his administration may arrive early at its goal of giving 100 million shots in 100 days.

And yet: At any moment, the US will pass the terrible milestone of 500,000 coronavirus deaths. Last month, one in five Americans surveyed said they were opposed to taking the vaccine (13 percent said they’d never take it; 7 percent only would if required). And globally, the vaccine rollout is going much more slowly. In December, The Economist’s Intelligence Unit predicted that many low-income countries won't receive their vaccines before next year, and last month, the World Health Organization’s director-general, Tedros Adhanom Ghebreyesus, warned the world is “on the brink of a catastrophic moral failure” for not sharing vaccines equitably with the Global South.

Summing up: This won’t be over soon. Between the slow pace of global vaccination and the rapid emergence of virus variants—potentially driven by the selective pressure that patchy vaccine coverage is putting on the virus—researchers and policymakers are beginning to admit that Covid-19 is here for good.

This requires a psychological reset. In the first year of the pandemic, we acted as though Covid was an unexpected guest, something that arrived without warning and could be packed up and sent away if we worked hard enough. It would be more realistic now to admit that the virus is an unwelcome permanent roommate. We are unlikely to force it to leave. But we may be able to keep it from taking over the house.

Accepting this possibility means that we have to start considering two lines of action at once. First, we need to do everything possible to reduce the number of illnesses and deaths occurring in this current emergency. Second, we need to admit those actions won’t be enough to chase Covid-19 from the world forever—what public health people would call eradication—and consider what it will mean for it to be a permanently present, or endemic, disease.

SARS-CoV-2 “just doesn't have the characteristics that we look for when we're talking about a virus that is able to be eradicated from the human population,” says Tara C. Smith, an epidemiologist and professor at the Kent State University College of Public Health. “Between the potential for animal reservoirs and the fact that it is asymptomatic so frequently, I think it’s going to be very difficult.”

Eradication is a lofty goal, so hard to achieve in public health that it has been managed for only one human disease: smallpox. (Rinderpest, a disease of cattle, has also been eradicated.) The generally accepted definition of eradication is that the transmission of a disease is brought to zero—by isolation, treatment, or a vaccine—leaving the pathogen no place to hide and effectively ending its life. Eradication campaigns for diseases beyond those two have faltered because vaccinations can’t penetrate the places the organisms shelter in the world: for yellow fever, in monkeys; for malaria, in mosquitoes; for tetanus, in soil. (Polio, the target of a 32-year international campaign, can hide quiescently in the guts of asymptomatic people. It got very close to eradication, but when the pandemic halted vaccination efforts, cases rebounded again.)

The Covid-19 virus has similar shelters: in the bats it originally jumped from, in some probable intermediate (and still unidentified) animal that helped it adapt from bats to humans, in the minks that have been identified as harboring it in several countries—and in whatever percentage of the human population remains unprotected by natural immunity or vaccine.

So there is no way to cast a net around Covid-19 and tighten it to nothing; its animal hosts will always provide it an escape hatch. However, it’s not actually useful to start thinking about alternate hosts until all of a disease’s potential human victims have been protected by vaccination—and so far, we are not remotely close. As long as people somewhere in the world are still waiting for their first shots, Covid-19 will have human hosts to reproduce in. And also, potentially, to mutate in, creating the kind of variants that are now appearing across the globe.

That raises the possibility that, as the virus changes, we’ll need to keep tinkering with vaccines to keep up with it. “I think most people feel that this will be something where likely for the next several years we’ll be getting a Covid-19 shot,” Alex Gorsky, the CEO of Johnson & Johnson, said earlier this month at a CNBC event. “Exactly what that shot is going to be comprised of, I don’t think we know today.”

If Covid cannot be a disease we try to squelch quickly—the way, for instance, we roll out vaccines to counter Ebola outbreaks—it has to become a disease we plan for, such as measles and influenza. With measles, we begin vaccinating in childhood. With the flu, we revaccinate annually, while tuning the vaccine’s contents to keep up with viral evolution. We vaccinate against those because they take such a toll. In the past 10 years, influenza has killed anywhere from 12,000 to 61,000 people per year in the US; globally, measles kills 140,000 each year.

We have no guarantee whether Covid-19, if it becomes endemic, will be as ferocious as measles, or mellow into something mild. Before the pandemic began, there were six coronaviruses known to infect humans: the original SARS from 2003; MERS, which arose in 2012; and four that cause seasonal illnesses. Those last four, which are now considered endemic, are responsible for about 25 percent of the colds we contract every winter, and they demonstrate that some coronaviruses can become something that we dislike, but don’t need to fear. (They have not always been mild, though. One of them has recently been linked to a worldwide epidemic in 1889 and 1890 of respiratory illness and neurological problems; it came down in history as the “Russian flu”—but that name was a guess at its cause, since flu viruses weren’t identified til 40 years later.)

A recent paper modeling the potential future of the novel coronavirus, written by postdoc Jennie Lavine of Emory University, attempts to forecast the ways that Covid-19 might behave in the future, based on data gathered from the four endemic coronaviruses, plus SARS and MERS. It finds that Covid-19 could reach the state that the four endemic strains now occupy, of causing mostly mild disease on a regular basis—but that outcome will depend on how the circulating disease behaves in children during their first infections, since it’s those first infections that set the immune system up to respond down the road.

That is the same function that vaccines perform, of course. Our bodies create multiple types of immunity in response to pathogens; it’s too soon, Lavine says, to gather the long-term data we’ll need in order to know whether Covid-19 vaccination and childhood infection both protect in such a way that any subsequent infections produce only mild disease.

But assume, for the moment, that the virus doesn’t become a mild infection like a cold, but remains an unpredictably dangerous one. That prospect makes it more urgent to defuse vaccine nationalism and to distribute doses worldwide as fast as possible, not just to protect people from illness, but to deprive the virus of hosts in which it can mutate.

Whether the new vaccines protect against infection and block the ability to transmit the virus to others is still an open question, though some data is beginning to show that some formulas might. The shots were authorized on the basis that they prevent serious disease, hospitalization, and death. If we successfully prevent those worst effects, we potentially transform Covid-19 into something more like influenza or other seasonal respiratory infections such as respiratory syncytial virus (known as RSV) or adenovirus—something that poses a risk at particular times of year, but, most of the time, doesn’t clog hospitals or close down ICUs.

“If you take away the risk of death, when you get enough people vaccinated, then Covid can become something that you plan for,” says Amesh Adalja, a physician and senior scholar at the Johns Hopkins Center for Health Security. “Hospitals will be attuned to the risk. We can develop a harm reduction framework to help people go about their activities in a safer manner. Once we can get severe disease taken care of, I think we will be as close to normalcy as we can hope for now.”

Projecting that we’ll be able to think about Covid-19 the way we do the flu—knowing what severity of illness we expect, and when—might be able to help us plan for its persistence. It might make mask-wearing normal for people with a case of the sniffles, the way it was in Asian nations before Covid-19 began. To the degree we return to offices, it might make people take sick days more seriously. Even more, though, it might help us imagine what structures and procedures we’ll have to create to get to a society in which we can live alongside endemic Covid long-term.

We are forced to change the flu vaccine every year because the virus continually alters its antigenic profile: As it runs into the immunity created by the flu shot, plus any immunity the population possesses from past infections, it evolves to get past that protection. But we know how flu is changing because a shared international network of reference laboratories, set up around the globe and overseen by the WHO, continuously monitors virus samples to detect what is emerging. And we know how to alter the vaccine in response because of collaborations between the WHO, CDC, and other national health agencies, which each year come to agreements on how the vaccine composition should be updated.

Discussion about the lessons contained in the first year of Covid have focused on how to detect the next pandemic early: Some experts have proposed a cross-national outbreak investigations agency, and the Biden administration’s new Covid-19 plan envisions a national epidemic forecasting center. But to live with Covid long-term, we’ll need different structures, ones that help us evaluate the virus’s ongoing threat once it has become a permanent part of our lives. Just as it hasn’t been around long enough to become endemic, it also hasn’t been long enough for us to imagine just what those structures should be. But it is not too soon to start.

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