Will the Delta Variant Peak and Burn Out?

Kathleen Doheny
August 04, 2021

When the Delta variant of the coronavirus was first identified in India in December 2020, the threat may have seemed too remote to trigger worry in the United States, although the horror of it ripping through the country was soon hard to ignore.

Within months, the Delta variant had spread to more than 98 countries, including Scotland, the U.K., Israel, and now, of course, the U.S. The CDC said this week the Delta variant now accounts for 93% of all COVID cases.

Fueled by Delta, COVID-19 cases, hospitalizations, and deaths are increasing in nearly all states, according to the latest CDC data. After the 7-day average number of cases dipped by June 22 to about 11,000, it rose by Aug. 3 to more than 85,000.

Some experts are heartened by the recent decrease in COVID-19 cases in the U.K. and India, both hard-hit with the Delta variant. COVID-19 cases in India peaked at more than 400,000 a day in May; by Aug. 2, that had dropped to about 30,500 daily.

Andy Slavitt, former Biden White House senior adviser for COVID-19 response, tweeted July 26 that if the Delta variant acted the same in the U.K. as in India, it would have a quick rise and a quick drop.

The prediction seems to have come true. As of Aug. 3, U.K. cases have dropped to 7,467, compared to more than 46,800 July 19.

So the question of the summer has become: "When will Delta burn out here?"

Like other pandemic predictions, these are all over the board. Here are five predictions about when COVID cases will peak, then fall. They range from less than 2 weeks to more than 2 months:

• Mid-August: Among the most optimistic predictions of when the Delta-driven COVID-19 cases will decline is from Scott Gottlieb, MD, former FDA director. He told CNBC on July 28 that he would expect cases to decline in 2-3 weeks -- so by August 11.
• Mid-August to mid-September: Ali Mokdad, PhD, chief strategy officer for population health at the University of Washington, says that, "Right now for the U.S. as a country, cases will peak mid-August" and then decline. He is citing projections by the university's Institute for Health Metrics and Evaluation. In its "most likely" scenario, it predicts COVID deaths will peak at about 1,000 daily by mid-September, then decline. (As of Aug. 3, daily deaths averaged 371.)
• September: "I am hoping we get over this Delta hump [by then]," says Eric Topol, MD, founder and director of the Scripps Research Translational Institute in La Jolla, CA, and editor-in-chief of Medscape. "But sometimes, I am too much of an optimist."
• Mid-October: Experts at the COVID-19 Scenario Modeling Hub, a consortium of researchers from leading institutions who consult with the CDC, say the Delta-fueled pandemic will steadily increase through summer and fall, with a mid-October peak.
• Unclear: Because cases are underestimated, "I think it is unclear when we will see a peak of Delta," says Amesh Adalja, MD, a senior scholar at the Johns Hopkins Center for Health Security. He predicts a decline in cases as "more people get infected and develop natural immunity."

The predictions are based on different scenarios, such as most likely or worst-case. Factors such as personal behaviors, public mandates, and vaccination rates could all alter the projections.

What a Difference Vaccination May Make

An uptick in vaccinations could change all the models and predictions, experts agree. As of Aug. 3, almost half (49.7%) of the total U.S. population was fully vaccinated, the CDC says. (And 80.1% of those 65 and over were.)

But that's a long way from the 70% or 80% figure often cited to reach herd immunity. Recently, Ricardo Franco, MD, of the University of Alabama at Birmingham, said at a briefing by the Infectious Diseases Society of America that the infectiousness of the Delta variant may mean the herd immunity threshold is actually closer to 90%.

Mokdad of the University of Washington estimates that by Nov. 1, based on the current rate of infections, 64% of people in the U.S. will be immune to a variant like Delta, taking into account those already infected and those vaccinated against COVID-19.

Justin Lessler, PhD, a University of North Carolina epidemiologist involved in the modeling hub, says if enough people get vaccinated, it could stop the Delta variant in its tracks. But that percentage is high.

"I am relatively confident that if we could get 90% or more of the eligible population vaccinated that we would see the epidemic begin to recede," he says.

It's a huge leap from 50%, or even 64%, to 90%. Could the Delta surge really motivate that many people to head to a vaccination site?

That's hard to predict, Topol says. Some unvaccinated people may feel like soldiers in a foxhole, he says, especially if they are in hard-hit states like Louisiana, and rush to get the vaccine as soon as possible. Others, hearing about the "breakthrough" cases in the vaccinated, may dig in their heels and ask, "Why bother?" as they mistakenly conclude that the vaccine has not done its job.

Roles of Public Policy, Individual Behavior

Besides an increase in vaccinations, individual behaviors and mandates can change the scenario. Doctors can remind even vaccinated patients that behaviors such as social distancing and masks still matter, experts say.

"Don't 'stress test' your vaccine, " Topol says.

The vaccines against COVID are good but not perfect and, he notes, they offer less protection if many months have passed since the vaccines were given.

The best advice now, Topol says, is: "Don't be inside without a mask."

Even if outdoors, depending on how close others are and the level of the conversation, a mask might be wise, he says.

Mokdad finds that "when cases go up, people put on their best behavior," such as going back to masks and social distancing.

"Unfortunately, we have two countries," he says, referring to the way public health measures and mandates vary from state to state.

Once the Delta Variant Subsides, What's Next?

It's not a matter of if there is another variant on the heels of Delta, but when, Topol and other experts say. A new variant, Lambda, was first identified in Peru in August 2020 but now makes up about 90% of the country's infections.

There's also Delta-plus, just found in two people in South Korea.

Future variants could be even more transmissible than Delta, "which would be a horror show," Topol says. "This [Delta] is by far the worst version. The virus is going to keep evolving. It is not done with us."

On the Horizon: Variant-Proof Vaccines

What's needed to tackle the next variant is another approach to vaccine development, according to Topol and his colleague, Dennis R. Burton, a professor of immunology and microbiology at Scripps Research Institute.

Writing a commentary in Nature published this year, the two propose using a special class of protective antibodies, known as broadly neutralizing antibodies, to develop these vaccines. The success of the current COVID-19 vaccines is likely due to the vaccine's ability to prompt the body to make protective neutralizing antibodies. These proteins bind to the viruses and prevent them from infecting the body's cells.

The broadly neutralizing antibodies, however, can act against many different strains of related viruses, Topol and Burton write. Using this approach, which is already under study, scientists could make vaccines that would be effective against a family of viruses. The goal: to stop future outbreaks from becoming epidemics and then pandemics.

References

SOURCE: Medscape, August 04, 2021. Ali Mokdad, PhD, chief strategy officer for population health, University of Washington, Seattle. Eric Topol, MD, executive vice president, Scripps Research; founder and director, Scripps Research Translational Institute, La Jolla, CA; editor-in-chief, Medscape. Justin Lessler, PhD, professor of epidemiology, University of North Carolina, Chapel Hill. Amesh Adalja, MD, senior scholar, Johns Hopkins Center for Health Security, Baltimore. Twitter: @ASlavitt, July 26, 2021. Nature: "Variant-proof vaccines -- invest now for the next pandemic." American Society for Microbiology: "How Dangerous Is the Delta Variant (B.1.617.2)?" Johns Hopkins University: COVID-19 Data Repository, COVID tracker. CDC: "COVID Data Tracker." CNN: "More infectious Delta variant makes up 83% of new coronavirus cases as vaccine hesitancy persists." National Geographic: "The Unusual Lambda variant is rapidly spreading in South America." WebMD, Medscape: "Delta Variant Could Drive Herd Immunity Threshold Over 80%." The Korea Herald: "Korea confirms first two cases of delta plus." NPR: "The Delta Variant Will Drive A Steep Rise in U.S. COVID Deaths, A New Model Shows." COVID-19 Scenario Modeling Hub.