When will the COVID-19 pandemic end? It depends on how you define end.

According to historians, pandemics typically have two types of endings: the medical, which occurs when the incidence and death rates plummet, and the social, when the epidemic of fear about the disease wanes.

In other words, an end can occur not because a disease has been vanquished but because people grow tired of panic mode and learn to live with a disease.

“When people ask, ‘When will this end?,’ they are asking about the social ending,” said Dr. Jeremy Greene, a historian of medicine at Johns Hopkins in Baltimore.

Allan Brandt, a Harvard historian, said something similar is happening with COVID-19: “As we have seen in the debate about opening the economy, many questions about the so-called end are determined not by medical and public health data but by sociopolitical processes.”

Bubonic plague has struck several times, once in the sixth century, again in the 14th century and a pandemic that struck in the late 19th and early 20th centuries. It died down, but it never really went away. In the United States, infections are endemic among prairie dogs in the Southwest and can be transmitted to people by fleas that carry the microbe. But such cases are rare and now can be successfully treated with antibiotics.

Among the diseases to have achieved a medical end is smallpox. But it is exceptional for several reasons: There is a vaccine; the virus, Variola minor, has no animal host, so eliminating the disease in humans meant total elimination, and its symptoms are so unusual that infection is obvious, allowing for contact tracing.

The 1918 flu is held up today as the example of the ravages of a pandemic and the value of quarantines and social distancing. The flu killed 50 million to 100 million people worldwide, preying on young to middle-aged adults. After sweeping through the world, it faded away, although experts aren’t sure why.

“Maybe it was like a fire that, having burned the available and easily accessible wood, burns down,” Yale historian Frank Snowden said.

Other flu pandemics followed — none so bad, but all nonetheless sobering. In the Hong Kong flu of 1968, 100,000 people in the United States died. That virus still circulates as a seasonal flu, but the fear that went with it is rarely recalled.

Will that happen with COVID-19?

One possibility, historians say, is that the coronavirus pandemic could end socially before it ends medically. People may grow so tired of the restrictions that they declare the pandemic over before a vaccine or effective treatment is found.

“I think there is this sort of social psychological issue of exhaustion and frustration,” Yale historian Naomi Rogers said. “We may be in a moment when people are just saying, ‘That’s enough.’ ”