Projecting the transition of COVID-19 burden towards the young population while vaccines are rolled out: a modelling study

ABSTRACT

ObjectivesSARS-CoV-2 infection causes most cases of severe illness and fatality in older age groups. In China, over 99% of individuals aged [>=]12 years have been fully vaccinated against COVID-19 (albeit with vaccines developed against historical lineages), while 65.0% children aged 3-11 years have been vaccinated their first doses (as of November 12, 2021). Here, we aimed to assess whether, in this vaccination landscape, the importation of Delta variant infections could shift the COVID-19 burden from adults to children. MethodsWe developed an age-structured susceptible-infectious-removed model of SARS-CoV-2 transmission dynamics to simulate epidemics triggered by the importation of Delta variant infections and project the age-specific incidence of SARS-CoV-2 infections, cases, hospitalisations, intensive care unit (ICU) admissions, and deaths. ResultsIn the context of the vaccination programme targeting individuals aged [≥]12 years (as it was the case until mid-October 2021), and in the absence of non-pharmaceutical interventions, the importation of Delta variant infections could have led to widespread transmission and substantial disease burden in mainland China, even with vaccination coverage as high as 97% across the eligible age groups. Extending the vaccination roll-out to include children aged 3-11 years (as it was the case since the end of October 2021) is estimated to dramatically decrease the burden of symptomatic infections and hospitalisations within this age group (54% and 81%, respectively, when considering a vaccination coverage of 99%), but would have a low impact on protecting infants (aged 0-2 years). ConclusionsOur findings highlight the importance of including children among the target population and the need to strengthen vaccination efforts by increasing vaccine effectiveness.