Impact of SARS-CoV-2 vaccination of children ages 5-11 years on COVID-19 disease burden and resilience to new variants in the United States, November 2021-March 2022: A multi-model study

Abstract

Background: The COVID-19 Scenario Modeling Hub convened nine modeling teams to project the impact of expanding SARS-CoV-2 vaccination to children aged 5-11 years on COVID-19 burden and resilience against variant strains.

Methods: Teams contributed state- and national-level weekly projections of cases, hospitalizations, and deaths in the United States from September 12, 2021 to March 12, 2022. Four scenarios covered all combinations of 1) vaccination (or not) of children aged 5-11 years (starting November 1, 2021), and 2) emergence (or not) of a variant more transmissible than the Delta variant (emerging November 15, 2021). Individual team projections were linearly pooled. The effect of childhood vaccination on overall and age-specific outcomes was estimated using meta-analyses.

Findings: Assuming that a new variant would not emerge, all-age COVID-19 outcomes were projected to decrease nationally through mid-March 2022. In this setting, vaccination of children 5-11 years old was associated with reductions in projections for all-age cumulative cases (7.2%, mean incidence ratio [IR] 0.928, 95% confidence interval [CI] 0.880-0.977), hospitalizations (8.7%, mean IR 0.913, 95% CI 0.834-0.992), and deaths (9.2%, mean IR 0.908, 95% CI 0.797-1.020) compared with scenarios without childhood vaccination. Vaccine benefits increased for scenarios including a hypothesized more transmissible variant, assuming similar vaccine effectiveness. Projected relative reductions in cumulative outcomes were larger for children than for the entire population. State-level variation was observed.

Interpretation: Given the scenario assumptions (defined before the emergence of Omicron), expanding vaccination to children 5-11 years old would provide measurable direct benefits, as well as indirect benefits to the all-age U.S. population, including resilience to more transmissible variants.

Funding: Various (see acknowledgments).

Keywords: COVID-19; Modeling; SARS-CoV-2; Scenario projection; Vaccination; Variant emergence.

Fig. 1

Projected cases, hospitalizations, and deaths for all ages at the national-level (September 12, 2021–March 12, 2022). Median ensemble projections for each scenario displayed as lines, 95% projection intervals displayed as shaded regions. Observed ground truth data available for model calibration (solid points) and after model fitting (open circles) through December 11, 2021 (after which Omicron became prevalent in the U.S., departing from specified scenarios). The start date for vaccination of children 5–11 years old, November 1, 2021, is indicated by a dashed line. See Fig. S1 for ensemble median and 50% projection intervals separated by scenario and the Round 9 tab of the COVID-19 SMH website for additional visualization functionality. Ensemble median, 50% and 95% credible intervals are provided for cumulative cases, hospitalizations, and deaths over the projection period in Supplemental Fig. S3.

Fig. 2

State-level ensemble projection performance from projection start date (September 12, 2021) through the observed weekly data available: A) before the assumed start of vaccination in 5–11 years old children (ending October 30, 2021; 6-week projection horizon) and B) after three months (ending December 11, 2021; 13-week horizon). Scenario A (childhood vaccination and no variant) projections are displayed. Projected cumulative cases vs. observed cumulative cases for all ages by state and normalized by state population. The red line marks where projected cumulative cases are equal to the corresponding state observations.

Fig. 3

Scenario comparison to evaluate vaccine benefits. Absolute difference in estimates for all age cases, hospitalizations, and deaths when vaccination of 5–11-year-olds occurs without (top) and with (bottom) the emergence of a more transmissible variant from meta-analysis with random effects. Projection results from each team are analyzed as separate studies and are identified by team name abbreviation (see Supplemental Information for full team names). The size of each model-specific square is proportionate to the weight given to that model in the meta analysis. Corresponding cumulative values from the end of the projection period (March 12, 2022) for each model are provided in Supplemental Table S3.

Fig. 4

Scenario comparison to evaluate vaccine benefits. Incidence ratio estimates for all age cases, hospitalizations, and deaths when vaccination of 5–11 year-olds occurs without (top – scenarios A and B) and with (bottom – scenarios C and D) the emergence of a more transmissible variant from meta-analysis with random effects. See Table 1 for scenario definitions. The size of each model-specific square is proportionate to the weight given to that model in the meta analysis. Corresponding cumulative values from the end of the projection period (March 12, 2022) for each model are provided in Supplemental Table S3.

Fig. 5

Comparison between younger-age projections and all-age projections for relative changes in cumulative cases where vaccination of 5–11-year-olds does not occur without (squares) and with (triangles) the emergence of a highly transmissible variant between November 1, 2021 and March 12, 2022. Younger-age groups considered are as follows: CU-AGE-ST (5–17 years), MOBS_NEU-GLEAM_COVID (0–11 years), USC-SlkJalpha (5–11 years), UVA-adaptive (0–17 years), UVA-EpiHiper (0–11 years).