Pandemic to end in common cold endemic: Study
Within the next few years, as the SARS-CoV-2 virus becoming endemic, Covid-19 may behave like other common-cold coronaviruses, affecting mostly young children who have not yet been vaccinated or exposed to the virus, according to new modeling results.
The observation comes at a time when the USA is reporting a growing number of children contracting Covid-19, with a corresponding spike in cases of respiratory syncytial virus (RSV), a contagious seasonal flu that is more common in the winter time.
However, because Covid-19 severity is generally lower among children, the overall burden from this disease is expected to decline.
“Following infection by SARS-CoV-2, there has been a clear signature of increasingly severe outcomes and fatality with age,” said Ottar Bjornstad, researcher from Pennsylvania State University.
“Yet, our modeling 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,” said the team’s results which appeared in the journal Science Advances.
Bjornstad explained that such shifts have been observed in other coronaviruses and influenza viruses as they have emerged and then become endemic. “For example, ongoing genomic work suggests that the 1889-1890 pandemic, sometimes known as the Asiatic or Russian flu — which killed one million people, primarily adults over age 70 — may have been caused by the emergence of HCoV-OC43 virus, which is now an endemic, mild, repeat-infecting cold virus affecting mostly children ages 7-12 months old,” he said.
Bjornstad cautioned, however, 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 disease.
“However, research on Covid-19 shows that vaccination provides stronger protection than exposure to the SARS-CoV-2 virus, so we encourage everyone to get vaccinated as soon as possible,” he said.
Specifically, the researchers examined disease burden over immediate, medium and long terms - 1, 10 and 20 years, respectively. They also examined disease burden for 11 different countries - including China, Japan, South Korea, Europe, Spain, United Kingdom, France, Germany, Italy, United States, Brazil and South Africa - that differed widely in their demographics. They used data from the United Nations for each of these countries to parameterise the model.
“Regardless of immunity and mixing, the population-level burden of mortality may differ among countries because of varying demographics,” said Ruiyun Li, postdoctoral fellow, university of Oslo. “Our general model framework allows for robust predictions of age-dependent risk in the face of either short or long-term protective immunity, reduction of severity of disease given previous exposure, and consideration of the range of countries with their different demographics and social mixing patterns.”
Jessica Metcalf, Associate Professor of ecology, evolutionary biology and public affairs, Princeton University, noted that this prediction is likely to hold only if reinfections produce only mild disease. However, she said, the burden of mortality over time may remain unchanged if primary infections do not prevent reinfections or mitigate severe disease among the elderly.
Interestingly, due to variations in demographics, the model predicts different outcomes for different countries.
“Given the marked increase of the infection-fatality ratio with age, countries with older population structures would be expected to have a larger fraction of deaths than those with relatively younger population structures,” said Nils Chr Stenseth, professor of ecology and evolution, University of Oslo.
“Consistent with this, for example, South Africa - likely due, in part, to its younger population structure - has a lower number of deaths compared to older populations such as Italy. We found that such “death disparities” are heavily influenced by demographics. However, regardless of demographics, we predict a consistent shift of the risk to the young.”