Since the beginning of the epidemic, researchers have discovered that it is the elderly who suffer most from severe forms of Covid-19. But are they also more likely to become infected with the coronavirus? Japanese epidemiologists have an answer to that.
The data collected since the beginning of the epidemic are irrefutable: the elderly suffer and die most from severe forms of Covid-19. This does not mean that other age groups are spared from the coronavirus, quite the contrary. The youngest suffer simply from less severe symptoms or are asymptomatic.
Japanese epidemiologists have questioned whether susceptibility to infection varies with age and whether it plays a role in the current epidemic. To this end, they have developed a mathematical model, the results of which are published in scientific reports.
The susceptibility to infection does not vary with age.
Researchers began by using a model to understand whether susceptibility to infection alone could explain the distribution of mortality observed in three countries – Japan, Italy, and Spain. These three countries were selected because they made their epidemiological data publicly available.
According to their model, the distribution of mortality can be explained only by susceptibility, but susceptibility depends on the R0(the average number of people infected by one infectious individual), the virus reproduction rate calculated at a specific time during the epidemic. However, the R0 of the three countries for the period considered last May is quite different. The R0 ranges from 2.4 to 3.3 for Italy, 1.7 for Japan, and 2.9 for Spain. The declared mortality rate (number of deaths per 100,000 inhabitants) was also different: 382.3 for Italy, 507.2 for Spain, and 13.2 for Japan.
Despite these differences, the age distribution of mortality is comparable among the three countries. Researchers concluded that susceptibility to infection does not vary with age. However, this does not completely exclude the possibility that older people are more susceptible to infection, but if this is the case, it does not seem to have a significant effect on the number of patients affected by Covid-19.
Although susceptibility does not seem to vary with age, the severity of the disease, the onset of symptoms, and mortality are well correlated with age. Age is then one of the most important co-morbidity factors in addition to obesity and the presence of chronic disease before infection.