Dr. Anthony Fauci, the top medical adviser to President Joe Biden, said this week that we are still in the first of five stages of the pandemic, and he cautioned against thinking we are further along than we actually are.

The first phase of the pandemic—or the “the truly pandemic,” according to Fauci—is “where the whole world is really very negatively impacted as we are right now,” he said on January 17 at the World Economic Forum’s Davos Agenda online conference.

The following four steps are deceleration, control, elimination, and finally eradication.

Here are the characteristics of the other four stages.

Deceleration

After the first phase comes deceleration—a slowdown in the number of newly confirmed cases.

Omicron cases have risen steeply and then dropped off in many countries where the variant took hold. In South Africa, the fourth Omicron-fueled COVID wave lasted only a total of three weeks, and COVID hospitalizations in England have already begun to recede, just one month after the almost-vertical climb starting mid-December.

Scientists from the U.K.’s Scientific Advisory Group for Emergencies (SAGE) have built models that show there may be a fresh wave of Omicron cases in early summer as people resume social activities and immunity wanes, but they argue cases are unlikely to rise as they did with Omicron, with the latest modeling noting another worst-case scenario of 4,000 people hospitalized a day is very unlikely to occur.

Some people are optimistic that natural immunity will cause the number of new cases to subside, but Fauci notes it is too soon to tell, and there could always be a new variant just around the corner.

“It is an open question as to whether or not Omicron is going to be the live virus vaccination that everyone is hoping for, because you have such a great deal of variability with new variants emerging,” he said.

Control

The next phase, following deceleration, is the control phase of the pandemic—or what some are referring to as endemicity. That means that COVID-19 would become integrated into the broad range of infectious diseases we commonly experience, like the flu or the common cold.

“Control means you have it present, but it is present at a level that does not disrupt society,” Fauci says.

He noted that he hopes this will be the case, but he added that it would be possible only if another variant that eludes the immune response does not emerge. Whether or not COVID will be endemic in 2022, Fauci responded: “The answer is, we do not know.”

Governments like Spain and Switzerland have already said that COVID-19 is becoming an endemic disease countries can manage like the flu.

But for COVID to become endemic, there can’t be any more surprises on the transmissibility and its virulence of the virus or any of its future variants.

“I don’t think there is anything predictable about coronavirus,” Lawrence Young, a virologist and professor of molecular oncology at Warwick Medical School, told Fortune.

“Entering an endemic phase is very different from what we’re experiencing at the moment,” Young said. “I think a lot of it is wishful thinking.”

Elimination

The elimination of a pandemic occurs when the virus still exists in the world but it has been eradicated from certain regions or countries. Fauci gives the example of polio, which has been eradicated from many countries in the Global North.

The world is still far from achieving that with COVID, scientists say.

“For a lot of people there has been this hope that there will be a day where victory will be declared. They will say, ‘Today was the end of COVID, and tomorrow we will live in a COVID-free world again.’ I think that is really unrealistic, and not feasible,” Dr. Wafaa El-Sadr, professor of epidemiology and medicine at Columbia University, previously told Fortune.

Eradication

The last stage, eradication, is nearly impossible to reach. Fauci notes smallpox was the only infectious human disease that has ever been eradicated, and he said outright that regarding COVID, “That’s not going to happen with this virus.”