How the coronavirus pandemic could end

• Many emerging viruses become part of the viral ecology. The four coronaviruses that cause the common cold are endemic, circulating in the population, and the influenza strains that cause seasonal flu predictably surge each year.
• The SARS outbreak in 2003 didn't go the same way due to biology and behavior: It was much less transmissible than the virus that causes COVID-19, countries contained it quickly, and it has pretty much disappeared.
• One virus, smallpox, was eradicated through widespread vaccination, and polio may be close, after decades of effort and billions in funding.

What's happening: The pandemic is deepening in the U.S., Europe and elsewhere in the world.

• Experts — from the U.K.'s chief scientific adviser to pharmaceutical CEOs to the WHO — increasingly say SARS-CoV-2 is likely to circulate in the population on a permanent basis, mainly due to the foothold the virus has already established.
• But what damage endemic COVID-19 causes will depend on different factors, including how often people are reinfected, vaccine effectiveness and adoption, and if the virus mutates in any significant way.

"If the vaccine is really effective, like the measles vaccine or the yellow fever vaccine, it's just going to land like a ton of bricks and suffocate this. Maybe not quite eradicate it — yellow fever and measles are not eradicated — but it'll be an utter game changer," UC Irvine epidemiologist Andrew Noymer says.

• But if the vaccines are less effective — as many experts expect for at least the first generation — COVID-19 may eventually behave more like the seasonal flu, Noymer says. (Still, the death rate of COVID-19 currently well eclipses that of the seasonal flu.)

Reinfection is "the big issue," says Columbia University's Jeffrey Shaman, who recently described how reinfection and other factors would affect the spread of SARS-CoV-2 if it became endemic.

• So far, there are just a handful of documented reinfection cases, but evidence about whether people retain their antibodies after infection is mixed, and a lot of unknowns remain about the likelihood of reinfection.
• The worst-case scenario would be that there isn’t a vaccine or long-lasting immunity and people get COVID-19 repeatedly and are just as likely to end up in the hospital as with initial infections, Shaman says.

"I would say COVID-19 is already endemic," says Larry Brilliant, an epidemiologist who worked to eradicate smallpox and now chairs the nonprofit Ending Pandemics.

• With about 59,000 new cases per day in the U.S. alone, Brilliant says "it is already everywhere."

• "It doesn’t really mean very much if it is endemic," he adds. "The real question is: How does it all end?"

Eventually, COVID-19 could end up in "the retirement village of coronaviruses," like HIV, which today can be treated to the point of elimination, or circulate at low levels and be kept in check with a vaccine, like measles, Brilliant says, laying out a handful of possible scenarios.

• Noymer says he suspects that after its "cataclysmic emergence," COVID-19 may eventually fade into a common cold after a decade or so.

What's next: "We have to work with it as a virus that we will be contending with for years possibly," Shaman says. "It doesn’t mean an effective vaccine or treatment won’t be developed. What it means is that holding out hope that we’re going to just get a vaccine and not doing anything else is not the level of preparation we need."

• Until we have an effective vaccine and better contact tracing and testing, Johns Hopkins University epidemiologist Justin Lessler says public health measures should continue encouraging the use of face masks and social distancing.
• If the disease does become endemic, Lessler says it's likely to eventually become more like a childhood infection because adults will gradually build an immunity. And since children tend to have fewer complications, "it will no longer be the same sort of burden to health that it is now."

The good news: Viruses can sometimes become milder with time, treatments are already becoming more effective and vaccines can be improved.

• "Right now we are frightened, depressed and on our back heels. We will be able to conquer this disease," Brilliant says. "It will be a matter of time and science."