Age-dependent effects in the transmission and control of COVID-19 epidemics

Nicholas G Davies; Petra Klepac; Yang Liu; Kiesha Prem; Mark Jit; Rosalind M Eggo

A great deal of concern has been directed toward the expected burden of COVID-19 in low and middle income countries (LMIC), which have lower population median age than many high income countries. Our results show that these demographic differences, coupled with a lower symptomatic fraction in younger ages, can result in proportionally fewer clinical cases than would be expected in higher-income countries with flatter demographic pyramids. This should not be interpreted as few cases in LMIC, because the projected epidemics are still very large, resulting in high numbers infected. Moreover, the particular relationship found with age here is drawn from high income countries, primarily in East Asia, and may reflect not only age, but also the increasing frequency of comorbidities with age. This relationship, therefore, may differ in LMIC for two key reasons: first, the distribution of non-communicable comorbid conditions-which are already known to increase the risk of severe disease from COVID-19 21 may be differently distributed by age, often occurring in younger age groups 34 , along with other possible risk factors such as undernutrition 36 ; and second, communicable comorbidities such as HIV 33 , TB coinfection (which has been suggested to increase risk 37 ), and others 38 may alter the distribution of severe outcomes by age. Observed severity and burden in LMIC may also be higher due to a lack of health system capacity for intensive treatment of severe cases.