Dr. Ashish Jha, President Joe Biden’s doctor and the White House’s COVID czar, told CBS’ “Face the Nation” on Sunday that U.S. health officials still “think we can get our arms around” the fast-moving disease, contending that the virus can still be managed via targeted vaccination and aggressive testing.

The Department of Health and Human Services is weighing whether it should declare a public health emergency, he added. 

But not all infectious disease experts are so optimistic. This weekend, the World Health Organization Director-General Dr. Tedros Adhanom Ghebreyesus declared the virus a public health emergency of international concern, while the head of the United States’ leading public health nonprofit told Fortune, “I think we’re already gone.”

“I won’t call it a lost cause, but I do think we need to step up our game,” Dr. Georges Benjamin, executive director of the American Public Health Association, said Monday.

Managing the disease is far from eradicating it, or eliminating any new foothold it may have already gained. By the time the world realizes monkeypox has entrenched itself outside of Africa, the battle against endemicity elsewhere will be over, some experts caution.

What does it mean for a disease to be endemic?

After nearly three years, COVID-19 has become endemic in the U.S. and around the world. That means the disease is regularly found in a particular area—in the case of COVID, that’s virtually all areas around the globe.

But there’s no agreed upon definition for endemicity, Dr. Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security, told Fortune on Monday. Conditions, however, typically take “a couple of years” before being deemed so, Benjamin and other experts say.

Case in point: the West Nile virus, a potentially fatal mosquito-borne illness discovered in Uganda in 1937 that arrived in New York City in 1999, eventually spreading throughout the U.S. and the Americas, from Canada to Venezuela.

But monkeypox may have already been circulating undetected outside of Africa for years—perhaps since 2018, some experts say, aided by early COVID-19 lockdowns that prevented people from seeking health care. Another factor that has aided covert spread: the mild presentation of some recent cases, causing it to be confused for chickenpox, or a variety of sexually transmitted infections.

“You can have a small lesion on your arm, and you may not get sick at all—but the next person you give it to could have a bad case and scarring,” Benjamin said, comparing the wide variety of severity in the condition to COVID. 

Endemicity, perhaps, but not the end of the story

Endemicity, however, wouldn’t mean the disease couldn’t be eradicated, as smallpox, another orthopox virus, was in 1980 after mass vaccination.

Vaccination can be used to halt transmission in countries monkeypox is new to, Adalja said—but policymakers must realize such a move is only a short-term solution.

“You worry now that because there’s an issue in Europe and the U.S., it’s hard for a world leader to say, ‘We’re going to go vaccinate Nigeria,’” he said.  But the vaccination of endemic countries is “how you control this from a long-range perspective.”

It’s exceedingly unlikely the world is anywhere near needing a smallpox-type effort to eradicate monkeypox, Benjamin said, though “hopefully someone is thinking about that type of response.”

A multipronged prevention and therapy strategy including post-exposure prophylaxis, antivirals, robust contract tracing, and “great data collection systems will help us get our hands around this much faster,” he said. “There’s no reason to think today we have to vaccinate the whole population.”

“We may be able to eliminate monkeypox to a baseline level it was at” before the current global outbreak, he said.

“You can get rid of an endemic disease, but it’s going to take work.”