In the next few years, COVID-19 may behave like other common-cold coronaviruses and affect mostly young children who have not yet been vaccinated or exposed to the virus, a modelling study published in the journal, Science Advances, revealed on Thursday.
The team, consisting of US-Norwegians stated that as severity of COVID-19 is generally lower among children, the overall burden from the infection is expected to reduce as the virus becomes endemic in the global population.
“Following infection by SARS-CoV-2, there has been a clear signature of increasingly severe outcomes and fatality with age,” said Ottar Bjornstad from the University of Oslo in Norway. “Yet, our modelling results suggest that the risk of infection will likely shift to younger children as the adult community becomes immune either through vaccination or exposure to the virus,” he said.
The team developed a “realistic age-structured (RAS) mathematical model” that integrates demographics, degree of social mixing, and duration of infection-blocking and disease-reducing immunity in order to analyse potential future scenarios for age-incidence and burden of mortality for COVID-19.
They analysed disease burden over immediate, medium and long terms of 1, 10 and 20 years respectively for 11 different countries – China, Japan, South Korea, Spain, UK, France, Germany, Italy, US, Brazil and South Africa, which differed widely in their demographics.
Using data from the United Nations for each of these countries to parameterise the model, the team found that the reproduction number (R), or the level of transmissibility on any given day is linked to the amount of mobility on that day.
The model also incorporates several scenarios for immunity, including both independence and dependence of disease severity on prior exposure, as well as short- and long-term immunity.
The researchers noted that in a scenario of long-lasting immunity, either permanent or at least 10 years, the young are predicted to have the highest rates of infection as older individuals are protected from new infections by prior infection.
The study noted that the shift to younger children has been observed in other coronaviruses and influenza viruses when they emerged and then became an endemic. Bjornstad cited example of the Russian flu, that killed one million people, mainly adults aged over 70, may have been caused by the HCoV-OC43 virus. The flu is now an endemic, mild, repeat-infecting cold virus that affects mainly children aged 7-12 months old.
However, Bjornstad cautioned that if immunity to reinfection by SARS-CoV-2 wanes among adults, disease burden could remain high in that group, although previous exposure to the virus would lessen the severity of infection. He stressed on the importance of vaccination for stronger protection against the virus.
“For many infectious respiratory diseases, prevalence in the population surges during a virgin epidemic but then recedes in a diminishing wave pattern as the spread of the infection unfolds over time toward an endemic equilibrium,” said Ruiyun Li, a postdoctoral fellow at the University of Oslo.
“Depending on immunity and demography, our RAS model supports this observed trajectory. It predicts a strikingly different age-structure at the start of the COVID-19 epidemic compared to the eventual endemic situation,” he added.
Jessica Metcalf, an associate professor at Princeton University, US, noted that this prediction is likely to hold only if reinfections produce only mild disease.
However, the burden of mortality over time may remain unchanged if primary infections do not prevent reinfections or mitigate severe disease among the elderly, she added.
Edited by Rupashree Ravi
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