COVID-19 of the Future: Endemic and Mostly in Young Children?

Damian McNamara

August 11, 2021

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Researchers predict SARS-CoV-2 could become endemic and primarily infect children, thereby shifting risk from older people to toddlers too young to be previously exposed or vaccinated.

Experience with similar beta coronaviruses and modeling across many countries and age groups allowed researchers to predict what COVID-19 could look like 1, 10, and 20 years from now.

"We are in the midst of a 'virgin pandemic,' a term epidemiologists use when the virus has not been seen before," senior author Ottar Bjornstad, PhD, told Medscape Medical News. The novelty of COVID-19 is similar to when measles was first introduced or when smallpox first came to the Americas, he added.

Although nothing is certain, researchers in the United States and Norway found general agreement among the models. The most likely situation is that COVID-19 will not be eliminated but rather transition to a global endemic illness.

"We don't have the data yet — everything, this so new," added Bjornstad, the J. Lloyd & Dorothy Foehr Huck chair of epidemiology and distinguished professor of entomology and biology at the Pennsylvania State University in University Park.

The study was published online August 11 in Science Advances.

If the predictions hold, most adults will be immune through vaccination or multiple exposures. The two circulating beta coronaviruses "cause a strong cold in children," Bjornstad said. "We get exposed to the cold viruses many times during our lifetimes — and through re-exposure [infections] are more mild.

"The death toll during the pandemic has been horrific, like some of the previous pandemics," Bjornstad said. Although it's still possible SARS-CoV-2 could continue to place the elderly at highest risk, "my colleagues and I think this is very unlikely."

Modeling Makes Sense

Dr Sindhu Mohandas

"The flu virus that caused a pandemic a century ago now circulates as a seasonal virus. It is indeed possible that COVID-19 will also eventually become endemic in the future and primarily affect populations without previous exposure or immunity to the infection," agreed Sindhu Mohandas, MD, pediatric infectious diseases specialist at Children's Hospital Los Angeles.

"It is also important to remember that we have a much more effective vaccine for COVID-19 than for flu," Mohandas said. "The availability and efficacy of COVID-19 vaccine in younger children in the future is likely to have a major impact on the evolution of the disease."

"There is a lot of circulation — and a lot of circulation in children and young adults — that is really fueling the pandemic now," Bjornstad said. The researchers believe that because COVID-19 severity is generally lower among children, the overall disease burden would also decline as SARS-CoV-2 becomes endemic.

"While there are some cases of severe disease in that age group, they are very rare," he added.

"It is becoming increasing likely that SARS-CoV-2 will not be eradicated but rather become an endemic, possibly seasonal, virus. Recognizing this eventuality, this article provides age-based modeling of what the future may hold," Taylor Heald-Sargent, MD, said when asked to comment.

Dr Taylor Heald-Sargent

"It makes sense that children will become the most susceptible group to SARS-CoV-2 as adults are able to develop immunity through infection or vaccination, but the child age group is continually repopulated with a naïve population," said Heald-Sargent, who is an infectious diseases attending physician at Lurie Children's Hospital in Chicago.

History Lesson

Respiratory disease pandemics of the past show that the age groups at greatest risk can shift over time. For example, the influenza pandemic of 1889 and 1890, also known as the Asiatic or Russian flu outbreak, killed about 1 million people.

Most of the deaths were among adults older than 70 years.

This pandemic may have been caused by emergence of the HCoV-OC43 human coronavirus. It is "now an endemic, mild, repeat-infecting cold virus affecting mostly children ages 7-12 months old," Bjornstad stated in a news release.

Calculations With Some Caveats

Bjornstad and colleagues looked at disease burden across 11 countries and regions, including the US, UK, Europe, China, and Brazil, and accounted for differences in demographics, including age.

"This is indeed a great statistical model aimed at predicting the evolution of COVID-19 disease in different populations. The ability to account for varying immunity, demographics, and social mixing can make it particularly useful," Mohandas said.

"However," she added, "we are dealing with too many unknowns in relation to COVID-19 which makes the applicability challenging at the current time. As we learn more about duration of immunity and severity of subsequent infections this can be a much more effective tool."

The limitations of the study include factors "unable to be accounted for in any model," Heald-Sargent said. For example, "variants could develop such as Delta that could drastically change the course of [a] pandemic to endemic transition. Our best chance at controlling, although not likely eradicating, SARS-CoV-2 is vaccinating everyone."

In February 2020, people still had hope for containment and eradication of SARS-CoV-2 like SARS-1, Bjornstad said. "I'm sure we'll be vaccinated against this beast into the future. We must vaccinate as hard and brutally as possible now."

Bjornstad said that endemic coronaviruses, in general, do not change over time as quickly as they can during an initial pandemic. They tend to be less deadly as well because of prior exposures.

"They cause, literally, 0.0001% mortality," he said.

The research was supported by the Huck Institute of the Life Sciences at Penn State and the Research Council of Norway.

Sci Adv. 2021;7:eabf9040. Full text

Damian McNamara is a staff journalist based in Miami. He covers a wide range of medical specialties, including infectious diseases, gastroenterology, and critical care. Follow Damian on Twitter: @MedReporter.

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