In a recent study posted to the medRxiv* preprint server, researchers evaluated the impact of immunizing five-11-year-old children against severe acute respiratory distress syndrome coronavirus 2 (SARS-CoV-2) on coronavirus disease 2019 (COVID-19) burden and resilience to new variants in the United States (US).
Background
COVID-19 vaccinations in individuals aged 12 years or older have considerably decreased the disease burden in the US. The COVID-19 Scenario Modeling Hub summoned several modeling teams in September 2021 to project the effect of expanding vaccination to children aged five to 11 years on COVID-19 burden and resilience against new SARS-CoV-2 variants.
About the study
The present study assessed the potential impact of immunizing children five to 11 years old against COVID-19 in the US.
The COVID-19 Scenario Modeling Hub was established in December 2020 to provide six-month-long COVID-19 projections in the US under different epidemiological scenarios and assumptions. For every scenario, modeling groups were called to predict weekly deaths, cases, and hospitalizations at national and state levels. The present paper describes the ninth round involving predictions of nine teams for the period between September 12th, 2021, and March 12th, 2022.
This round considered four scenarios: children with or without vaccination commencing on November 1st, 2021, and those with and without a novel variant hypothetically with 50% higher transmissibility by November 15th, 2021. Among the immunized children, uptake rates reflected those of the Centers for Disease Control and Prevention (CDC) for children aged between 12 to 17 years.
If vaccine effectiveness (VE) estimates were absent for children when scenarios were developed, VE was assumed to match those of older ages and remained similar for the hypothetical and the Delta variants. Additional assumptions involving seasonal effects, waning immunity and non-pharmacological interventions were at the teams’ discretion.
Probability projections were reported by all teams for all scenarios, outcome metrics, location, and week over the 26-week prediction period. Ensemble projections were made by linear pooling. Additionally, the authors conducted a meta-analysis to summarize the predicted benefits of immunizing children.
Results
The multi-modal aggregation study findings indicate that if a new variant did not emerge, COVID-19 cases, deaths, and hospitalizations would decrease across ages nationally through March 2022. The models projected that childhood immunization would enhance overall immunity with lower COVID-19 incidence (7.2%), hospitalizations (8.7%), and deaths (9.2%) across ages. In the presence of a more transmissible variant, greater relative reductions in cumulative hospitalizations, deaths, and cases would occur among children relative to the total US population.
The ensemble predicted decreasing COVID-19 incidence rates from September through December 2021. State-level projections of cumulative cases for a scenario with vaccinated children without a new variant between September 12th and October 30th, 2021, correlated with reported data. However, the observed patterns deviated from the ensemble-projected decrease in November 2021. Particularly, the state-level findings exceeded model predictions for the deaths and cases during this period.
The ensemble scenarios that assumed the rise of a 50% more transmissible variant than the Delta variant in November 2021 would gradually and moderately increase cumulative deaths and cases by early 2022. If a new variant did not emerge, cases would decline to levels similar to those observed in June 2021, and the predicted deaths would decrease to lesser than one per 100,000 individuals weekly by March 12th, 2022.
Assuming robust VE against the Delta strain and the hypothetical novel variant, the model predicted that immunizing children would continue to decrease viral transmission, hospitalizations, and cases. From November 1st, 2021, to March 12th, 2022, in the absence and presence of a new variant, the models projected an aversion of 430,000 cases (7%) and 860,000 cases (10%) in the US by immunizing children, respectively.
Additionally, the models predicted that vaccinating children would reduce hospitalizations by 8.7% and 12% without and with a novel variant, respectively. These values corresponded to an absolute decline of 47,000 and 93,000 hospitalizations, respectively. Likewise, childhood immunization would decrease the overall US mortality by 12% and 9% with and without a new variant, respectively. These predicted effects varied substantially at the state level, with an average estimated decrease in cases of 5.8% and 11% without and with a new variant, respectively.
Conclusion
To summarize, using projected assumptions, expanding vaccination to children aged five to 11 would confer a significant direct advantage to them and indirect advantages to the entire US population with decreased COVID-19 severity and increased resilience.
*Important notice
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
