COVID-19 Transmission Under the Public Health Radar: High Prevalence in Young Adults for COVID-19 Pandemic Wave 1

PURPOSE: Compare reported data on age specific rates of SARS-CoV-2 infections in countries from several continents to identify differences in age specific incidence of reported cases in different countries. METHODS & MATERIALS: Data on age-specific case incidence of SARS-CoV-2 derived from publicly available databases from selected countries in Europe, North America, Australasia, and Asia were collected and analysed to identify and evaluate trends in reported age specific distribution of morbidity from SARS-CoV-2 in countries for which data was available. RESULTS: Data for laboratory confirmed COVID-19 cases from South Korea, Australia, New Zealand, Japan and the Netherlands exhibited essentially identical profiles, with a bimodal distribution that shows highest rate of confirmed SARS-CoV-2 infections among individuals in the 20-29 years age cohort (21%-27% of total), and a second lower peak for the 50-59 or 60-69 age cohorts (16-18% of total), while preliminary data from China, United States and Sweden exhibited a unimodal distribution with highest rate of positive individuals for the 50-59 age cohort. CONCLUSION: There is increasing evidence that individuals < 30 years of age may be playing a highly significant role in the facilitation and amplification of COVID-19 transmission in countries worldwide. Data reported from the first wave of the COVID-19 Pandemic in at least 5 countries (South Korea, Australia, New Zealand, Japan, Netherlands) demonstrated that greater attention should be paid to the frequency and epidemiological importance of COVID-19 infections among young adults in the 20-29 year age cohort, because individuals in this age range comprise a large proportion (21%-27%) of the known laboratory confirmed COVID-19 cases in these countries, and perhaps other countries for which reliable data are not yet available. The epidemiological importance of COVID-19 infections among young adults and adolescents in amplifying and facilitating the proliferation of the COVID-19 Pandemic has been systematically underestimated in many countries, because of low rates of testing among asymptomatic individuals and low rates of severe disease or mortality among individuals <30 years of age. Clarifying and understanding the epidemiological dynamics of SARS-CoV-2 transmission among individuals in younger age cohorts will help in determining control strategies at the individual and population levels.