The coronavirus is here to stay, researchers say

Researchers at the University of Oslo along with colleagues across the globe have created a mathematical model that allows them to look at how the coronavirus situation may develop over time.

The “disease burden”, as it is called, is affected by factors such as the age distribution in the population, along with the amount of immunity and social interaction.

If a large part of the adult population develops good immunity to COVID-19, children will be the individuals who become infected to a greater extent. Young people usually get mild cases.

“Immunity builds up in the population, except for young people who may be exposed to this for the first time,” Nils Chr. Stenseth, a biologist and professor at the University of Oslo, said to sciencenorway.no.

“As a result, we wonder if the coronavirus will eventually become a childhood disease,” Stenseth said.

Stenseth worked on the new study, which has been published in Science Advances.

Age and immunity

The researchers used the model to look at how COVID-19 will develop in a population over the course of one, 10 and 20 years.

“What we have done is to create an age-structured model that has components for whether a person is susceptible to the disease and reflects the fact that mortalities are different, depending on the person’s age,” he said.

Stenseth said another aspect the researchers included is how socially active different age groups are.

“Older people don’t interact in the same way that young and middle-aged people do. Kids have a lot of contact with their parent’s generation, and so on,” Stenseth said.

The researchers also looked at what happens if immunity to the coronavirus is either short-lived or long-lasting.

The researchers also accounted for people who become infected a second time and whether or not a new infection will likely cause a milder illness than the previous infection.

Since the immune system has already trained itself to fight the virus, any new infection can lead to milder disease.

Like other coronaviruses

If immunity to COVID-19 is long-lasting and protects against serious illness, the modelling shows that the coronavirus will eventually circulate most in children.

The burden of disease in society will then decrease.

Within a few years, COVID-19 may behave like other coronaviruses, which usually result in milder colds. The virus will probably affect young children to a greater extent who haven’t yet had the virus or been vaccinated, says Ottar Bjørnstad, a professor at Penn State University in the US, to Titan.uio.no.

Bjørnstad was also involved in the study.

Forskning.no (in Norwegian) has previously written about four other largely harmless coronaviruses that circulate in humans.

It is speculated that one of them, HCov-OC43, was behind a pandemic called the Russian Cold in 1890. Researchers in 2005 calculated that the virus jumped from animals to humans and began to spread around 1890.

“Today, this is a mild virus that causes mild cold symptoms and that mostly infects children,” Bjørnstad said in the Titan.uio.no article.

Vaccinating young people

The researchers have not included vaccination as part of the model, but looked more broadly at immunity in general.

Stenseth said that this is nevertheless relevant for vaccinated people.

“ When you are vaccinated, you’ll be immune for a certain period, and you don’t know exactly how long it is. Older people in the population have resistance, are immune, while the younger people in the population are not, ”Stenseth says.

“That's why it's actually very important to start thinking about vaccinating younger people. The vaccine has now been approved for children as young as 12. But it’s hoped that younger children will also be able to be vaccinated. It's a matter of time, I would think,” he said.

A gloomier picture

If immunity to coronavirus is short-lived and doesn’t provide protection against serious illness in the event of a new infection, the picture will be different, the modelling shows.

"In this grim scenario, excess mortality due to severe reinfections due to declining immunity will continue until more effective pharmaceutical tools are available," said one of the other researchers behind the study, Jessica Metcalf from Princeton University, in a press release.

Countries with old populations are hit harder

The modelling also showed there was a difference in how hard different countries were hit in an early phase. This had a lot to do with how many older and young people are in a country’s population.

The researchers modelled eleven countries: China, Japan, South Korea, Spain, the United Kingdom, France, Germany, Italy, the United States, Brazil, and South Africa.

“South Africa has a young population and comes out relatively well in relation to what they would otherwise have done, while Spain and Italy have an old population and come out very poorly from the coronavirus pandemic, at least during the initial phase. So age means a lot,” Stenseth said.

The researchers believe their model will be useful for authorities as they prepare for the situation ahead and for future pandemics. New information can be entered into the model when more is known.

Think the virus is here to stay

It’s unclear whether the world will be able to eradicate the coronavirus completely.

So far, humans have managed to eradicate only one infectious disease: smallpox.

The coronavirus may end up being endemic. It will then not disappear completely but circulate in parts of the global population and remain at a stable level.

Nils Chr. Stenseth says it is difficult to say for certain whether the virus will be eradicated. But he is pretty convinced that the coronavirus is here to stay.

“It is very difficult to eradicate this kind of virus. We could perhaps almost eradicate it in our part of the world, especially in Norway. But the virus will always be imported again, and in large parts of the world, such as Africa, there are few vaccines available. The virus may continue to exist in some parts of the world with a very high probability,” Stenseth said.

In its latest risk assessment, the Norwegian Institute of Public Health concurs:

“SARS-CoV-2 cannot be eradicated in Norway or in the world. The long-term perspective is that the virus will enter an endemic phase where we can experience smaller waves in the winter as a result of immune evasion, seasonal effects and immune weakening over time, not unlike the patterns we see in influenza.”

Translated by Nancy Bazilchuk.

Read the Norwegian version of this article on forskning.no.

Reference:

Ruiyun Li, Jessica E. Metcalf, Nils Chr. Stenseth & Ottar N. Bjørnstad: “A general model for the demographic signatures of the transition from pandemic emergence to endemicity,” Science Advances, 11 August 2021.