- The United States is still seeing more than 50,000 new cases of COVID daily.
- “I think that it’s pretty unlikely that we’re going to eliminate it — at least in the short term — because there are still many, many people worldwide who have never had SARS-CoV-2 and are still susceptible to it,” says Angela Rasmussen, a virologist at the Vaccine and Infectious Disease Organization at the University of Saskatchewan.
- Vaccines work best at the community level. We all need to do our part to make sure SARS-CoV-2 comes under control.
Amid the rush to vaccinate the world against SARS-CoV-2, speculation on the virus’s future mutates, replicates, and spreads as well, in a petri dish of conversation:
Will we eliminate SARS-CoV-2? Eradicate it? Will we reach herd immunity — or a different sort of equilibrium? Will it become a mild annoyance — another common cold? Might new variants be more dangerous for children? Might some people get sicker with repeat infections?
In this episode of EPIDEMIC with Dr. Céline Gounder, researchers discuss the future of COVID, and what it might look like as an endemic virus.
The rush for herd immunity
One frequent topic during the pandemic has been “herd immunity.” We reach herd immunity when, even once the virus infects someone, nearly everyone around that person is already immune to it — either through exposure or vaccination — so that the virus has no opportunity to spread. Jennie Lavine, a postdoctoral epidemiologist and infectious-disease researcher at Emory University, uses damp firewood as a metaphor: “If you were trying to make a fire and most of the sticks were wet,” she says, “you wouldn’t be able to start the fire, even if you put a lot of sparks in there.” The threshold for herd immunity — the proportion of wet sticks needed to make a fire impossible — differs with each virus. Since the threshold for SARs-CoV-2 is high — perhaps over 80 percent — we may never reach it through vaccination alone.
For one thing, even as vaccine distribution continues, new variants arise that may be resistant to current vaccines. What we can hope for, says Lavine, is transient herd immunity: “If you can vaccinate really quickly in a population,” she says, “you can get this … refractory period where there’s not enough susceptibles for a little while.”
In other words, by reducing the number of people vulnerable to the virus, even for a short time, we reduce the likelihood of mutant viruses. This, of course, is a global effort: “The sooner we can get this under control globally,” says Angela Rasmussen, a virologist at the Vaccine and Infectious Disease Organization at the University of Saskatchewan, “the sooner it’s not going to be a problem for anybody.”
From pandemic to endemic
If herd immunity is not attainable with SARs-CoV-2, then what happens next? In one likely scenario, SARs-CoV-2 becomes consistently present, but less of a threat.
Take, for example, the case of OC43 — one of four widely circulating coronaviruses that today’s adults have been routinely exposed to since childhood. These days, OC43 is similar to the common cold. But the virus may have once been deadly, explains Lavine: Researchers now hypothesize that OC43 emerged in the late 1800s — the same time the “Russian Flu” raged, killing around 1 million people. If, as many researchers suspect, the “Russian Flu” actually was OC43 — deadly in its early waves, and, a century and a half later, no longer a threat — then OC43 offers one hopeful trajectory for SARS-CoV-2. But its diminution took decades.
The West Nile virus offers a more recent analog, says Jeffrey Shaman, a professor of environmental health sciences at Columbia University’s Mailman School of Public Health. West Nile first emerged in New York City in 1999. Within five years, it had spread across North America, and is now endemic to the region.
Shaman thinks SARs-CoV-2 might, in the long run, be a seasonal virus, though its patterns remain to be seen: “Are there going to be areas of the world where they’re just seeing it all the time?” he asks. “Or … where it’s going to appear every year?”
Along with questions about infection patterns come questions about reinfection, and how long immunity — whether due to vaccination or exposure — will last. Shaman notes that around 90 percent of people have antibodies against the four most common endemic coronaviruses, such as OC43. But reinfection with these viruses — even with the same virus, and even within a year — is common. Some people have become reinfected with SARS-CoV-2 within a year as well. Shaman’s takeaway? Natural immunity to coronaviruses is generally short-lived — and this may be true with SARS-CoV-2 as well.
But repeat infections may not be as scary as they seem: Reinfections are generally much milder. Lavine outlines one scenario for the future of SARS-CoV-2: “Everyone would get infected for the first time as a young kid. It would be mild because they’re a kid and then they would get reinfected throughout life. And it would be mild because they had some pre-existing immunity.” But we don’t yet know how well natural immunity will work — or whether reinfection with new variants could actually make people sicker, as happened in one recent study. And while SARS-CoV-2 has thus far not been dangerous for most children, the virus could, in theory, change in ways that make children’s infections more severe.
‘A decades-long arms race’
These unknowns — and the ways in which the virus can change unpredictably — could make the fight against SARS-CoV-2 “like a decades-long arms race between the immune system and the virus as it continues mutating,” says Rasmussen, the University of Saskatchewan virologist.
Many have wondered whether SARS-CoV-2 could become a seasonal malady, much like the flu. But influenza crosses species — traveling in migratory birds, for instance — and this, along with its genetic structure, allows it to mutate far more rapidly, with wildly unpredictable effects on its potency and transmission. While coronaviruses can mutate, they don’t recombine their genetic material with one another in quite the same way that influenza does, which makes for fewer strains of coronaviruses. This leaves Rasmussen hopeful that “once we manage to control transmission on a global scale, especially, we really won’t see that much more of SARS-CoV-2.”
Still, with over 50,000 new cases daily in the United States alone — and the virus still raging in India, Brazil, and elsewhere — new variants continue to arise. Whether vaccination offers an end to SARS-CoV-2, a dilution of the viral threat, or simply a reprieve, it remains our best hope for preventing both serious infection and the creation of more deadly strains.