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Age-dependent effects in the transmission and control of COVID-19 epidemics
Nicholas G Davies1, Petra Klepac2, Yang Liu2
1Department of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, London, UK. nicholas.davies@lshtm.ac.uk.
Insights
Children under 20 have lower COVID-19 susceptibility and clinical manifestation rates than adults. Interventions targeting children may have limited impact on SARS-CoV-2 transmission due to these age-related differences.
Area of Science:
- Epidemiology
- Mathematical Modeling
- Infectious Disease Dynamics
Background:
- The COVID-19 pandemic disproportionately affected adults, with a notably lower proportion of cases observed in children.
- Observed age disparities in COVID-19 cases suggest potential differences in susceptibility or clinical symptom presentation between children and adults.
Purpose of the Study:
- To quantify age-specific susceptibility to SARS-CoV-2 infection and the clinical manifestation fraction in different age groups.
- To evaluate the impact of age-related factors on the overall transmission dynamics and burden of COVID-19.
Main Methods:
- An age-structured mathematical model was developed and fitted to epidemic data from multiple countries (China, Italy, Japan, Singapore, Canada, South Korea).
- The model estimated age-specific susceptibility and the probability of developing clinical symptoms upon infection.
Main Results:
- Individuals under 20 years of age exhibit approximately half the susceptibility to SARS-CoV-2 infection compared to adults over 20.
- The clinical manifestation fraction increases with age, from 21% in 10-19 year olds to 69% in those over 70.
- Interventions focused on children may have a limited effect on overall SARS-CoV-2 transmission, especially if subclinical infections are less transmissible.
Conclusions:
- Age-specific susceptibility and clinical presentation significantly influence the expected global burden of COVID-19.
- Demographic differences, particularly population age structure, impact per capita clinical case incidence, with older populations potentially facing disproportionately higher case numbers without effective control measures.
- Understanding these age-related epidemiological factors is crucial for effective public health strategies and resource allocation during pandemics.
Abstract:
The COVID-19 pandemic has shown a markedly low proportion of cases among children1-4. Age disparities in observed cases could be explained by children having lower susceptibility to infection, lower propensity to show clinical symptoms or both. We evaluate these possibilities by fitting an age-structured mathematical model to epidemic data from China, Italy, Japan, Singapore, Canada and South Korea. We estimate that susceptibility to infection in individuals under 20 years of age is approximately half that of adults aged over 20 years, and that clinical symptoms manifest in 21% (95% credible interval: 12-31%) of infections in 10- to 19-year-olds, rising to 69% (57-82%) of infections in people aged over 70 years. Accordingly, we find that interventions aimed at children might have a relatively small impact on reducing SARS-CoV-2 transmission, particularly if the transmissibility of subclinical infections is low. Our age-specific clinical fraction and susceptibility estimates have implications for the expected global burden of COVID-19, as a result of demographic differences across settings. In countries with younger population structures-such as many low-income countries-the expected per capita incidence of clinical cases would be lower than in countries with older population structures, although it is likely that comorbidities in low-income countries will also influence disease severity. Without effective control measures, regions with relatively older populations could see disproportionally more cases of COVID-19, particularly in the later stages of an unmitigated epidemic.
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