Before the new coronavirus, there was SARS and MERS: Do epidemics ever really end?

The coronavirus outbreak has reached 48 countries and sickened over 83,000 people as of Friday. Total deaths neared 3,000, the majority in China, but also 26 in Iran, 17 in Italy, and 13 in South Korea.

Alongside the rapid escalation of the coronavirus crisis has come the hope that—at some point—it will cease. South Korean president Moon Jae-in said on Feb. 13 that the virus would “disappear before long”—days before South Korea’s cases leapt up. And U.S. President Donald Trump in early February twice made the unfounded claim that the virus would likely “go away” in April because of the warmer weather.

Even the language used to describe this outbreak and those of the past, like “the 2003 SARS epidemic,” suggests that prevalence of such diseases are restricted to a specific point in time. But we shouldn’t assume the coronavirus will have a neat and tidy conclusion.

“Of course, yes, in an epidemiological sense epidemics do end. But the end of an epidemic doesn’t remove the threat. The potential for future outbreaks is always there,” said Robert Peckham, a University of Hong Kong professor who researches histories of infectious disease, epidemics, and global pandemic threats.

“Conventional ways of thinking about diseases—that they emerge, flare up into epidemics, and then end—is misleading,” Peckham said. “We need to reimagine this outbreak narrative and begin to understand that diseases are here to stay.”

Eradication, elimination, endemic

There are three possible outcomes of the coronavirus outbreak, according to Jonathan Quick, adjunct professor of global health at the Duke Global Health Institute and author of The End of Epidemics: The Looming Threat to Humanity and How to Stop It.

First, the disease could be eradicated, which would be a “permanent worldwide reduction to zero new cases of the disease through deliberate efforts,” Quick said, like smallpox, which was eradicated in 1980.

A commuter wears a face mask on a street in Karachi on February 28, 2020. The coronavirus has spread to 48 countries in a few short months.

But eradicating the coronavirus—which would require an effective vaccine to eliminate human cases, and efforts to eliminate all animal sources—is “virtually impossible” right now, Quick said. The animal source of the virus is still a mystery. Other unknowns include the virus’s incubation period, the possibility of reinfection, whether antiviral drugs can help treat the illness, and whether the number of reported cases is accurate.

The second possibility is that the coronavirus is eliminated, which means cases fall to zero in a defined geographical area. This would be possible in the long term—five years at the earliest—with a highly effective vaccine, Quick said.

Pharmaceutical companies are racing through clinical trials to develop antiviral treatments and vaccines for the new coronavirus, but any drugs they develop won’t be released on the market for several months at the earliest.

Until a vaccine is developed, Quick said, the most likely outcome is the third: that the coronavirus becomes endemic.

When viruses are endemic, there is a continued occurrence of the disease in an area or population. The common cold is endemic—infections occur regularly, and have done so throughout human history. If the coronavirus turns endemic, it will no longer be an epidemic, a label given when there’s an unusual jump in the number of cases.

It appears that SARS-COV-2, the virus that causes the COVID-19 illness, “will be with us for a long time and likely cause periodic season respiratory disease like other common human coronaviruses,” said Gregory Gray, an infectious disease epidemiologist at Duke University.

Did SARS end?

COVID 19 is part of a family of coronavirus pathogens that’s caused well-known diseases like SARS, MERS, and the common cold.

According to researchers, the current coronavirus is closely related to the strain that caused the SARS outbreak. The first SARS cases were reported in late 2002; the World Health Organization declared SARS officially contained on July 5, 2003. (The date marked 20 days—or two 10-day incubation periods—since the last confirmed case.) Rapid and effective WHO action and strong responses in the 27 affected countries brought SARS under control, Quick said.

“Based on country surveillance reports, the human chains of SARS virus transmission appear to have been broken everywhere in the world,” the WHO announcement read. But, it cautioned, “the world is not yet SARS-free.”

Covid-19 Cases Continue To Rise In Japan
Women wearing face masks and novelty hats leave Tokyo Disneyland on Feb. 28, the day it announced it will close until March 15th because of concerns over the Covid-19 virus.
Carl Court—Getty Images

The last known SARS case occurred in China at the end of April 2004, in a lab where researchers had handled samples of the virus.

“[SARS] was effectively eliminated, in that there have been no naturally occurring outbreaks of it since,” Quick said.

Nevertheless, SARS remains on the WHO list of diseases with “epidemic potential”—diseases that pose a public health risk because of a lack of countermeasures, and which the WHO believes are a priority for public health research and development.

“The immediate challenge we’re facing is how to manage the COVID-19 outbreak. But tomorrow we could be facing an avian flu pandemic, outbreaks of MERS, or Ebola,” Peckham said.

The WHO list also includes the coronavirus MERS, which was first reported in 2012. Cases have declined since 2016, but 19 MERS infections and eight MERS-related deaths occurred as recently as the period between Dec. 1 2019 and Jan. 31 2020. There is no vaccine for MERS.

And after SARS was contained, incentive to roll out a vaccine faded, research lost funding, and vaccine development efforts were shelved.

“SARS was often held to be a turning point, but I don’t think there’s an understanding of the scale of the challenge we face,” Peckham said.

More must-read stories from Fortune:

Trump budget cuts could become a big problem as coronavirus spreads
China cracking down on VPNs in coronavirus crisis
China tries to restart economy as outbreak slows. Is it heading back to work too soon?
—5 reasons coronavirus statistics seem inconsistent
—Coronavirus may be the straw that breaks the back of oil fracking

Subscribe to Fortune’s Brainstorm Health newsletter for daily updates on biopharma and health care.

Subscribe to Well Adjusted, our newsletter full of simple strategies to work smarter and live better, from the Fortune Well team. Sign up today.