Would counting only the deaths of people under the age of 65 provide a more reliable overview of the true level of transmission of SARS-CoV-2? This is what researchers from the Institut Pasteur, the CNRS and the University of Cambridge suggest.
- Not counting the deaths of people under 65 would provide a better tool for comparing countries since older people are over-represented in some regions.
- In retirement homes, the circulation of the virus is more active and dangerous than in the rest of the population.
- The researchers established a new model in which they classified the deaths according to the age of the patients.
Is our vision of the circulation of the coronavirus misleading? Researchers from the University of Cambridge, the Institut Pasteur and the CNRS suggest that counting only the deaths of people under 65 from Covid-19 will be a more reliable indicator for assessing infection rates. . “The very strong spread of Covid-19 in retirement homes in Europe and the incomplete data on mortality among the elderly in some countries make it difficult to rely on the total number of deaths to compare the level circulation of the virus in different countries”, they wrote in a press release published on November 3 by the Institut Pasteur. The researchers presented their results Nov. 2 in the journal Nature.
Difficult to compare figures between countries
By counting only deaths in people under the age of 65, the researchers suggest that one would get a better insight into the circulation of the virus. In addition, it would provide a more accurate comparison tool between countries. “A simple comparison of the total number of deaths between countries can be misleading in its representation of the true level of SARS-CoV-2 transmission. Most deaths are in the elderly, but these are the least comparable data across countries”, continues Megan O’Driscoll, doctoral student in the Department of Genetics at the University of Cambridge and first author of the article.
In some countries, the virus affects older people disproportionately. The authors note that in the UK, Canada and Sweden, nursing home residents account for 1 in 5 Covid-19 related deaths. Conversely, in Asia and South America older people have officially a much lower mortality rate than Europe. The researchers speculate that this could be because “causes of death in older populations are less likely to be investigated and reported, as the priority of these countries is to contain the epidemic.”
A new model based on patient age
The researchers argue that among the elderly, especially those who live in retirement homes, the circulation of the virus is more active and dangerous than elsewhere. “Nursing homes are communities of isolated people, and once the virus enters them, it can spread rapidly, leading to higher levels of infection than in the general population. We are seeing an excessively large number of deaths from Covid-19 in this high age bracket, especially in countries with many retirement homes”, specifies Dr Henrik Salje, from the Department of Genetics at the University of Cambridge, co-lead author of the report. These people are also more fragile and more at risk of dying following an infection, resulting in an imbalance with the rest of the population.
The researchers established a new model in which they categorized deaths by patient age through 22 surveys in 45 countries. These surveys also allowed them to better estimate the number of people infected by estimating the proportion of a population that has developed antibodies against the coronavirus. “By analyzing the relative risk of death from Covid-19 according to age, we found that many countries shared the same age-specific mortality profile in people under 65.. We were able to use this information to more reliably reconstruct the number of infections in the different countries, even those for which no seroprevalence survey was carried out.”, justified Simon Cauchemez, head of the Mathematical Modeling of Infectious Diseases Unit at the Institut Pasteur and co-lead author of the study.
In the first depictions of virus transmission in the population under 65, the researchers “estimate that at 1er September this year, an average of 5% of the population of the countries studied was infected with SARS-CoV-2”. This model also shows that mortality rates differ by country. “For example, people living in Slovenia or Denmark appear to have a lower probability of death from SARS-CoV-2 infection than that measured in New York.”, continue the researchers.
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