Shadowless Dreams

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“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.  

At this point, how long immunity to COVID-19 will last is unclear; the virus simply hasn’t been infecting humans long enough for us to know. But related coronaviruses are reasonable points of comparison: In SARS, antibodies—which are one component of immunity—wane after two years. Antibodies to a handful of other coronaviruses that cause common colds fade in just a year. “The faster protection goes away, the more difficult for any project to try to move toward eradication,” Grad told me.

This has implications for a vaccine, too. Rather than a onetime deal, a COVID-19 vaccine, when it arrives, could require booster shots to maintain immunity over time. You might get it every year or every other year, much like a flu shot.

Even if the virus were somehow eliminated from the human population, it could keep circulating in animals—and spread to humans again. SARS-CoV-2 likely originated as a bat virus, with a still-unidentified animal perhaps serving as an intermediate host, which could continue to be a reservoir for the virus. [...] 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.”

"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. Over time, SARS-CoV-2 becomes just another seasonal respiratory virus, like the four other coronaviruses that cause a sizable proportion of common colds: 229E, OC43, NL63, and HKU1. These cold coronaviruses are so common that we have likely all had them at some point, maybe even multiple times. They can cause serious outbreaks, especially in the elderly, but are usually mild enough to fly under the radar. One endgame is that SARS-CoV-2 becomes the fifth coronavirus that regularly circulates among humans. [...]

"With a virus, there is a general trade-off between how contagious it is and how deadly it is. SARS and SARS-CoV-2 are illustrative points of comparison: The earlier virus killed a much higher proportion of patients, but it also did not spread as easily. And what a virus ultimately wants to do is keep spreading, which is much easier to do from a live, walking host than a dead one. “In the grand scheme of things, you know, a dead host doesn't help the virus,” says Vineet Menachery, a coronavirus researcher at the University of Texas Medical Branch. The other four coronaviruses may also be less deadly because we have all encountered them as children, and even if our immunity does not prevent us from getting them again, it may still prevent severe disease. All of this, along with immunity from vaccines, means that COVID-19 is likely to become far less disruptive down the line. [...]

"Influenza might be another useful point of comparison. 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. “But so is influenza with us, and for the most part, flu doesn't shut down our societies. We manage it.”