A research group led by Associate Professor Ryosuke Omori of the Research Center for Human and Veterinary Infectious Diseases, Hokkaido University, used a mathematical model of infectious disease epidemics to examine the phenomenon in which severely ill and dead people are biased toward the elderly in the new coronavirus infection.As a result, it was found that the susceptibility to infection (susceptibility to infection) does not depend on age.
It has been commonly reported worldwide that severe and fatal cases of new coronavirus infections are common among the elderly.The causes are "because the elderly are easily infected, the severity and death are biased toward the elderly", or "the susceptibility to infection does not depend on the age, but the susceptibility to becoming severe after the infection is established is the elderly. There are two possible reasons: "It's so expensive."Therefore, the research group examined which of these explanations was more plausible.
The research group used a mathematical model of age-specific coronavirus epidemics to explore what aggravation and age-dependent deaths are needed to observe an age distribution of epidemic-independent deaths. construction.In this mathematical model, we also considered the difference in ease of contact with people depending on age and the restriction of behavior outside the home due to the epidemic of the new coronavirus.Also, paying attention to the phenomenon that the age distribution of deaths is almost the same even when compared in Italy, Spain, and Japan, where the epidemic scales are significantly different as of May 2020, this mathematical model is used for deaths in these three countries. Estimated the susceptibility to infection by age by applying to the data of age distribution in Spain.From the estimated values, we discussed the possibility of the mechanism of aggravation and death of the new coronavirus.
As a result, it was confirmed that under the assumption that "the mortality rate does not depend on the age, but the susceptibility to infection is higher in the elderly", the phenomenon that the severity and the occurrence of death are biased toward the elderly can occur. Under these conditions, the age distribution of mortality was highly epidemic-dependent and did not match the epidemic-independent age distribution observed in Italy, Spain, and Japan.
On the other hand, assuming that "the susceptibility to infection does not depend on age, but the mortality rate is higher in the elderly", the age distribution of mortality is almost unaffected by the scale of the epidemic, which is consistent with the observation data.
In addition, under the two assumptions that "the mortality rate is constant regardless of age" or "the rate of symptoms is constant regardless of age", it is applied to the data of the age distribution of deaths in the three countries, and by age of infection. I tried to estimate the susceptibility to infection.Then, it was suggested that both assumptions were unrealistically very different estimates and were not valid.
From these results, it is considered that the severity of the new coronavirus infection and the mortality tend to be biased toward the elderly, because the susceptibility to the progression of the medical condition such as the mortality rate and the rate of symptoms varies depending on the age. I understand.
This study suggests that "susceptibility to infection" is age-independent, which may have contributed to the elucidation of the mechanism of aggravation and death.The development of therapeutic methods is expected to develop by elucidating the age-dependent mechanism of disease progression in the future.
Paper information:[Scientific Reports] The age distribution of mortality from novel coronavirus disease (COVID-19) suggestions no large difference of susceptibility by age
