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IHME Expert Predicts New but Less Severe COVID Surge This Winter

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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 (IHME) of the University of Washington, Seattle, Washington, which accurately forecast the COVID-19 waves last winter and summer.

But other infectious disease experts are more optimistic about the future in regard to the pandemic.

Ali Mokdad, MD, an epidemiologist who is chief strategy officer for population health at the University of Washington, told Medscape Medical News that 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 low by spring, he said.

Unless a new variant emerges and the current vaccines are less potent against it, the winter surge will be considerably less severe than that of last winter, Mokdad said. “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. So we’ll see a rise in infections and hospitalizations, but not to the level of last summer and winter.”

IHME estimates that at the peak of last winter’s surge, there were about 340,000 cases a day, including undetected cases. IHME predicts that at the peak of the new wave this winter, there will be around 250,000 cases a day, Mokdad said.

“We expect the mortality, which peaked out around 2000 deaths a day in September [and then dropped], will go up to about 1300 at the peak [in January], then start coming down,” he said.

Seasonality Seen as Factor

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

First, fewer than 60% of the US 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. Winter in the US and in most of the Northern Hemisphere happens at a time when we have holidays, and we travel and get together. When you consider that we still have a lot of people who are resisting the vaccine and masks, we’re not in good shape for winter,” Mokdad said.

Peter Katona, MD, clinical professor of medicine at the David Geffen School of Medicine, University of California, Los Angeles (UCLA), and adjunct professor of public health at the UCLA Fielding School of Public Health, told Medscape Medical News that he can’t predict what will happen in the next few months.

But he said that 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, Ann Arbor, Michigan, and professor of medicine in the Division of Infectious Diseases, told Medscape Medical News that the global data are insufficient to determine whether or not 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 said.

With COVID-19 case rates plummeting, Malani said she sees a continuing “progression toward endemicity.” On the other hand, she cautioned, a sizable portion of the population remains unvaccinated.

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 said.

Katona put the number at 95% for the Delta variant. He noted that 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? That depends partly on the resistance to the virus of unvaccinated people who have been previously infected with COVID. All three of the experts said that for some portion of this group, the level of immunity will still be high.

To calculate the immunity in the population, one cannot 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. 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.

It’s difficult to measure the level of population immunity on the basis of antibody studies, Katona said. “Neutralizing antibodies go away after a few months, but that doesn’t mean that other parts of the immune system aren’t working. That’s why measuring the result — whether you get really sick or not — is the ultimate parameter we have to measure.”

Mokdad agrees that seroprevalence studies are inadequate. The antibodies people develop when they get sick wane over time, he said, but it’s unclear “how much immunity has been memorized by your T cells and B cells. Once you’re exposed to the virus, it may take just 1 day to recreate these antibodies and go after the virus. That we don’t know yet.”

Whether a person has been vaccinated or has natural immunity from prior infection, he added, immunity will wane, and “the waning of natural immunity [against Delta] should be similar to what we’re seeing with the vaccines.”

Katona, though, said that immunity against severe illness lasts longer among the vaccinated.

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 said. “In that sense, the US 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 said.

Vaccination of Children a Major Factor

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

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

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 noted 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 said.

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

Mokdad believes that having children vaccinated is a “very important” factor that could ameliorate the winter surge and bring us closer to herd immunity. Other factors that would have a positive effect, he said, are an increase in the percentage of eligible people receiving booster shots and more uniform mask wearing across the country.

Mandates for publicly and some privately employed workers to get vaccinated will also help, Katona observed. Such mandates have already led to an increase in the number of people who have been vaccinated.

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