Nov. 2, 2021 -- Another surge of COVID-19 is likely to hit the United States this winter, according to experts at the Institute for Health Metrics and Evaluation of the University of Washington, which accurately forecasted the COVID-19 waves last winter and summer.

But other infectious disease experts are more optimistic about the future of the pandemic.

Ali Mokdad, MD, an epidemiologist and chief strategy officer for population health at the University of Washington, says he and his colleagues expect the next surge to begin near the end of November and to peak in the second half of January.

The wave will probably end in March, and the COVID-19 case rate should be fairly next spring, he said.

Unless a new variant emerges which current vaccines are less potent against, the winter surge will be considerably less severe than that of last winter, Mokdad says.

"The proportion of cases to mortality and hospitalization will be higher than it was before because of the vaccines. The vaccines are highly effective against hospitalization and mortality, less effective against infection.,” he says.

At the peak of last winter's surge, the institute estimates there were about 340,000 cases a day, including undetected cases. At the peak of the predicted new wave this winter, there will be around 250,000 cases a day, Mokdad says.

"We expect the mortality, which peaked out around 2,000 deaths a day in September [and then dropped], will go up to about 1,300 at the peak [in January], then start coming down," he said.

Seasonality a Factor

Mokdad offered two reasons why he believes that a winter COVID-19 wave is inevitable.

First, fewer than 60% of the U.S. population has been fully vaccinated. "So 40% of the people are not vaccinated. Of those, some have been infected with the Delta variant, so they have some immunity, although it wanes. If you look at the 40% who are susceptible, that's enough to sustain the virus. They could get Delta at any time.

"The second factor is winter. We're moving indoors, and we're more likely to be indoors without masks,” he says.

Winter forces many to spend more time indoors and brings holidays, travel, parties and family gatherings, often without masks.

“We're not in good shape for winter," Mokdad says.

Peter Katona, MD, clinical professor of medicine at the David Geffen School of Medicine at UCLA says he can't predict what will happen in the next few months.

But he said on the basis of data he's seen from around the world, "COVID doesn't seem to be very seasonal. There's a little bit of seasonality that comes in the fall, but it's not like flu, which is very seasonal."

Preeti Malani, MD, chief health officer at the University of Michigan, says global data is insufficient to determine whether COVID-19 is seasonal.

Despite the colder weather that will force people to spend more time indoors, "I expect the holiday season will be pretty normal" in terms of people feeling comfortable about getting together, she says.

Herd Immunity Threshold

To reach herd immunity — the point at which COVID-19 can be managed and controlled — 85% of the population must have immunity to the virus, Mokdad says.

Katona put the number at 95% for the Delta variant. He says the number is lower for other variants.

Considering that only about 58% of Americans have been fully vaccinated to date, how far are we from that herd immunity threshold? It depends partly on the resistance to the virus of unvaccinated people who have been previously infected with COVID-19. All three of the experts say that for some portion of this group, the level of immunity will still be high.

To calculate the immunity in the population, you can’t simply add the percentage of fully vaccinated people to the percentage of those who were infected and survived, Katona said.

"We're pretty clear now that vaccine-induced immunity is much better than natural disease-induced immunity,” he says. “So you do have to add them together, but you don't add them together equally. You have to come up with a formula to figure that out in a precise way, especially since many people get infected and don't even know it," he explained.

Malani believes we're well on our way to herd immunity, ironically because the United States has suffered so greatly from COVID-19.

"Natural immunity does help somewhat [to reach herd immunity]," she says. "In that sense, the U.S. is ahead of many other countries because so many people have already been infected here."

After four or five waves of COVID in the United States, "most people have been exposed to the virus, even if they haven't had symptoms. Vaccination plus natural immunity are moving us toward the herd immunity threshold," Malani says.

Vaccination of Children a Major Factor

One factor that could help move us in that direction, the experts agree, is to get children and adolescents vaccinated. Nearly a quarter of the US. population is younger than 18. Fifty-four percent of 16- to 17-year-olds and 47% of 12- to 15-year-olds have already been vaccinated, according to the CDC.

The government is now preparing for a massive rollout of vaccines for children aged 5 to 11. .

However, only 27% of parents of 5- to 11-year-olds say they will definitely have their children vaccinated against COVID-19, according to a Kaiser Family Foundation survey. Thirty-three percent have a wait-and-see attitude, and 35% say they either will not allow their kids to get shots or will do so only if required.

Katona says there are three reasons for parents to have their children vaccinated: To prevent them from getting sick, to prevent them from getting "long COVID," and to reduce transmission of the disease.

"The more kids who get vaccinated, even if it's only a third [of those eligible], will be better than no kids getting vaccinated," he says.

If no complications are reported in the early round of vaccination, he said, a growing number of children will likely get their shots.