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Even as COVID cases continue to rise, owing to the highly contagious Delta variant, a number of Wall Street analysts have been predicting that the peak of the Delta wave in the U.S. is coming soon.

“Our latest projection indicates daily COVID-19 cases in the U.S. will continue to steadily rise, peaking at 250-300K/day 25-27 days from now and beginning to decline meaningfully just before Labor Day,” wrote RBC Capital Markets analysts in a mid-August report.

Where are these numbers coming from? And are we really nearing the end of the fourth (and possibly final) wave of COVID-19, or are we just gearing up for another devastating pandemic winter? The answer comes down to a few different variables.

Even as the Delta variant overwhelms ICUs in the South, some models—including one of the most widely used from the Institute for Health Metrics and Evaluation (IHME) at the University of Washington—are optimistically predicting that we’ve reached the crest of the Delta wave, and that COVID-19 cases and deaths will begin to fall in the coming weeks, bottoming out in December.

IHME’s projections are based on rapidly rising immunity, both from vaccines and infections, as the Delta variant roars across the country. Ali Mokdad, a professor of health metrics sciences at IHME, predicts that by December, 71% of Americans will have antibodies to the coronavirus one way or another, which will be enough to prevent a fifth wave.

“According to our estimates, we have peaked, and we’re coming down as a country. Of course, it varies by state, but as a country, we said we would peak in the third week of August, which has happened, and it’s coming down,” Mokdad said. “We don’t expect another surge in winter. We expect cases will go up a little bit in winter but not much. Mortality will not go up in winter, because of the vaccine.”

Mokdad added that an important caveat to these projections is that no new variants emerge that reduce the protection conferred by vaccines or previous infections.

Currently, 52% of eligible Americans are fully vaccinated, and that number is now rising at a faster clip after bottoming out in July. According to the White House, there was a 70% increase in August in the average number of first doses administered each week. Vaccine mandates following full approval by the FDA of the Pfizer vaccine will likely continue this trend.

In places with low vaccine uptake, particularly the South, sky-high transmission rates will eventually leave few people untouched by the virus, causing the surge to burn out.

But some experts aren’t so sure that these trends will be enough to prevent a winter spike, although they say it’ll be much more manageable in places with high rates of vaccination.

“I would be pretty surprised to see this peak really start coming down,” said Eleanor Murray, an assistant professor of epidemiology at Boston University. “Short term, I think there are two options: One is that maybe we’re getting to a sort of plateau where we’ll remain high but at a roughly stable level of cases for a little while before it starts coming down after that. The other is that any kind of turning of the curve is just a momentary blip, and we’re still going to be heading up.”

The reopening of schools is one factor that will likely cause cases to rise. Children 12 and under are still not eligible for the vaccines, and some conservative state governments have prevented schools from implementing protective measures, such as mask mandates. While children typically have milder cases, some states are currently experiencing a record number of pediatric hospitalizations owing to COVID-19. Children can also pass the virus on to adult family members, contributing to further spread in areas with low vaccination rates.

In the U.K., which several analysts pointed to as an indicator of what’s to come in the U.S., a spring surge spurred by Delta plummeted once children were on summer vacation. However, now that British children are back in the classroom, case numbers are creeping up again.

Another factor is holiday travel, which triggered the third wave last year starting in November and persisting through January.

“Coronaviruses are somewhat seasonal—not as seasonal as flu, but they are somewhat seasonal—probably driven by human contact networks,” said William Hanage, an associate professor of epidemiology at Harvard University. “What that means is that we can expect to see more cases over the coming months as humans make more contacts, and more of them indoors. And Delta is highly infectious, so it’s really going to take advantage of that.”

This doesn’t mean vaccines and natural immunity won’t do anything. In places with higher vaccination rates, like Vermont, there will likely be less of a spike. In other states currently experiencing a surge in cases, such as Florida and Texas, Delta may have burned through enough of the community that the peak will be over soon. But other states could be on the path to another bad winter—unless behavioral interventions are put into place.

“Vaccines are the single most useful thing we can do to preserve our own lives and those of those close to us and to minimize disruption to our communities. They are not going to be sufficient to completely exclude Delta,” Hanage said. “In order to prevent uncontrolled Delta transmission of the sort that has been leaving ICUs getting overwhelmed or close to overwhelmed in a lot of places, I think we need to be prepared for some further nonpharmaceutical interventions.”

In other words, how quickly this wave recedes (and whether it’s immediately followed by another one) is ultimately up to us.

“As the fall goes on, people are going to realize that we have to go back to masking; we have to go back to limiting our contacts with other people,” said Murray. “That coupled with vaccines could mean that we don’t have a winter wave at all this year. It’s up to us to decide what happens.”