Projecting the Transition of COVID-19 Burden Towards the Young Population While Vaccines are Rolled Out: A Modelling Study

Abstract

Background: SARS-CoV-2 infection causes most cases of severe illness and fatality in older age groups. In China, over 85% of individuals aged ≥12 years have been vaccinated against COVID-19 (albeit with vaccines developed against historical lineages), while children aged 0–11 years are currently not eligible for vaccination (as of September 2021). Here, we aimed to assess whether the importation of Delta variant infections will shift the COVID-19 burden from adults to children.Methods: We developed an age-structured SARS-CoV-2 transmission model to simulate epidemics triggered by the importation of Delta variant infections. We then used the model to quantify the age-specific incidence of SARS-CoV-2 infections, cases, hospitalisations, intensive care unit (ICU) admissions, and deaths.Findings: Under a vaccination program targeting 12+ years old individuals, symptomatic SARS-CoV-2 infections and hospitalisation are projected to shift towards children and young adolescents, with 13% of symptomatic infections and 30% of hospitalisations occurring in those aged 0–11 years. Extending the vaccination roll-out to include children aged 3–11 years is estimated to dramatically decrease the burden of symptomatic infections and hospitalisations within this age group (54% and 81%, respectively), but would have a low impact on protecting infants (aged 0–2 years).Interpretation: In the absence of non-pharmaceutical interventions, the importation of Delta variant infections could lead to widespread transmission and substantial disease burden in mainland China, even with vaccination coverage as high as 97% of the population aged ≥12 years. Our findings highlight the need to strengthen vaccination efforts by simultaneously extending the target population and elevating vaccine effectiveness.Funding: Funding was provided by the Key Program of the National Natural Science Foundation of China and the National Institute for Health Research (NIHR) Declaration of Interest: H.Y. received research funding from Sanofi Pasteur, GlaxoSmithKline, Yichang HEC Changjiang Pharmaceutical Company, Shanghai Roche Pharmaceutical Company, and SINOVAC Biotech Ltd. M.A. received research funding from Seqirus. Except for research funding from SINOVAC Biotech Ltd, which is related to the data analysis of clinical trials of immunogenicity and safety of CoronaVac, the others are not related to COVID-19. All the other authors have no competing interests.