Although misinformation has been a prominent feature of the COVID-19 pandemic, the virus energizing it (SARS-CoV-2) is uniquely difficult to characterize. This is especially true of prognosis and transmissibility.
It didn’t take long for clinicians to recognize the elderly as a disproportionately impacted group. However, up until relatively recently, it was assumed that this demographic additionally contracted SARS-CoV-2 more easily compared to the young.
A new study published last week in the journal Scientific Reports repudiates this assumption with comprehensive data from Japan, Spain, and Italy.
The mortality rate (number of deaths per 100,000) was located around 382.3 for Italy, 507.2 for Spain, and 13.2 for Japan back in May. Given that the age distribution of COVID-19 deaths were comparable between all three regions, we can conclude that the severity and appearance of symptomatic COVID-19 are linked with age, but age likely says very little about the likelihood of an individual contracting the virus responsible for the respiratory illness.
There are conditions associated with advanced age studied to weaken one’s immune system against foreign bodies, though this establishes a correlative relationship between age and coronavirus transmission, not a causal one.
“Among Italy, Spain, and Japan, the age distributions of COVID-19 mortality show only small variation even though the number of deaths per country shows large variation. To understand the determinant for this situation, we constructed a mathematical model describing the transmission dynamics and natural history of COVID-19 and analyzed the dataset of mortality in Italy, Spain, and Japan. We estimated the parameter which describes the age-dependency of susceptibility by fitting the model to reported data, including the effect of change in contact patterns during the epidemics of COVID-19, and the fraction of symptomatic infections,” the authors wrote in the new paper.
“Our study revealed that if the mortality rate or the fraction of symptomatic infections among all COVID-19 cases does not depend on age, then unrealistically different age-dependencies of susceptibilities against COVID-19 infections between Italy, Japan, and Spain are required to explain the similar age distribution of mortality but different basic reproduction numbers,” they said.
The presentation of COVID-19 is dependent on several factors, meaning there isn’t any be-all metric instructive of disease severity. Age certainly contributes to clinical risk assessments, but the latest report proves there is still a lot more ground to cover before all relevant parameters are fully understood.
“The contribution of age-dependency to susceptibility is difficult to use to explain the robust age distribution in mortalities by COVID-19, and it suggests that the age-dependencies of the mortality rate and the fraction of symptomatic infections among all COVID-19 cases determine the age distribution in mortality from COVID-19. Further investigations regarding age-dependency on the fraction of infections becoming symptomatic is required to understand the mechanism behind the mortality by COVID-19 infections,” the authors conclude.
This means that although the elderly are overwhelmingly more likely to develop severe manifestations of COVID-19, they don’t appear to be any more susceptible to infection–at least not directly.