Risk of Infection and Hospitalization Among Vaccinated and Unvaccinated Children and Adolescents in New York After the Emergence of the Omicron Variant

In the US, 12.3 million youth aged 18 years and younger were diagnosed with COVID-19 by April 7, 2022.¹ Studies conducted before the Omicron variant’s emergence indicated that the BNT162b2 vaccine is safe and effective in preventing COVID-19 outcomes in persons aged 5 years and older.^2-5 Compared with adolescents aged 12 to 17 years (30-μg doses), less is known about vaccination outcomes for children aged 5 to 11 years (10-μg doses), who were fully vaccinated only after the emergence of Omicron.

Linking 4 New York state databases for COVID-19 vaccinations, cases, and admissions, this analysis compared 2 outcomes among fully vaccinated (≥14 days after primary series completion) vs unvaccinated youth (partially vaccinated excluded) in the age groups 5 to 11 and 12 to 17 years: cases, defined as positive nucleic acid amplification test or antigen results; and hospitalizations (eMethods in the Supplement).

Cases and hospitalizations were enumerated for weekly cohorts of fully vaccinated and unvaccinated individuals for each age group from November 29, 2021, to January 30, 2022. Within each age group, incidence rate ratios (IRRs) were calculated, comparing unvaccinated vs vaccinated rates.

Case rates for youth achieving fully vaccinated status between December 13, 2021, and January 2, 2022, were estimated by time since vaccination across the period including January 3 through 30, 2022, and compared with unvaccinated with IRR during each period, separately for each age group (eFigure in the Supplement).

Statistical significance of IRRs was evaluated with exclusion of 1 in 95% CIs (eMethods in the Supplement). Boosted adolescents were included in weekly cohorts but not analyses of time since vaccination. Analyses were conducted with SAS version 9.4 (SAS Institute), with 95% CIs estimated with OpenEpi and Excel. The New York State Department of Health institutional review board determined this surveillance activity was exempt from review and the need for patient consent.

As of January 30, 2022, 365 502 children aged 5 to 11 years were fully vaccinated (mean [SD] age, 8.3 [2.0] years; 51% boys) and 997 554 were unvaccinated (mean [SD] age, 7.8 [2.0] years; 51% boys). Among adolescents aged 12 to 17 years, 852 384 were fully vaccinated (mean [SD] age, 14.6 [1.6] years; 50% boys) and 208 145 were unvaccinated (mean [SD] age, 14.6 [1.7] years; 53% boys). During observation, 140 680 cases of COVID-19 and 414 hospitalizations were observed among children aged 5 to 11 years; among adolescents aged 12 to 17 years, there were 154 555 cases and 671 hospitalizations (Table).

For adolescents aged 12 to 17 years, the unvaccinated vs vaccinated IRR against cases declined from 6.7 (95% CI, 6.2-7.2) the week of November 29 to 2.9 (95% CI, 2.8-3.0) the week of December 13 (Omicron 19% sequences), and declined further to 2.0 (95% CI, 1.9-2.2) by January 24 (Omicron >99% sequences) (Table). For unvaccinated vs fully vaccinated children aged 5 to 11 years, the IRR was 3.1 (95% CI, 2.7-3.6) the week of December 13 and declined to 1.1 (95% CI, 1.1-1.2) by January 24. Hospitalizations were higher in unvaccinated than fully vaccinated individuals by the week of January 24, with IRR of 1.9 (95% CI, 0.9-4.8) for children aged 5 to 11 years compared with 3.7 (95% CI, 2.1-6.5) for those aged 12 to 17 years.

For 13 or fewer days after full vaccination, the IRR for unvaccinated vs fully vaccinated children aged 12 to 17 years was 4.3 (95% CI, 3.4-5.3), but by 28 to 34 days it was 2.3 (95% CI, 1.9-2.7) (Figure). For children aged 5 to 11 years, the IRR at 13 days or fewer was 2.9 (95% CI, 2.7-3.1) and at 28 to 34 days it was 1.1 (95% CI, 1.1-1.2).

The risks of infection and hospitalization were elevated for unvaccinated vs vaccinated children aged 5 to 11 and 12 to 17 years, although the risk declined as Omicron became more prevalent. Protection declined with time since vaccination. These results complement recent findings of reduced vaccine effectiveness for adolescents against the Delta variant² and the dual effects of the variant and waning protection against infection, with sustained protection against hospitalizations.⁴

Study limitations include that home testing was not reported and could affect case numbers if testing practices differed by vaccination status. Booster doses were not accounted for in the weekly analysis but comprised a small percentage of vaccinations (12.5% of adolescents by January 31, 2022). In the analysis period of time since vaccination, children aged 5 to 11 years were vaccinated soon after vaccine approval; and those aged 12 to 17 years, relatively later. The 2 groups may differ in test seeking or exposures.

These findings support efforts to increase vaccination coverage in children and adolescents and review dosing strategies for children aged 5 to 11 years.⁶

Accepted for Publication: April 18, 2022.

Published Online: May 13, 2022. doi:10.1001/jama.2022.7319

Corresponding Author: Vajeera Dorabawila, PhD, Division of Epidemiology, Bureau of Surveillance & Data Systems (BSDS), Corning Tower Room 754, Empire State Plaza, Albany, NY 12237 (vajeera.dorabawila@health.ny.gov).

Author Contributions: Drs Dorabawila and Rosenberg had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

Concept and design: All authors.

Acquisition, analysis, or interpretation of data: Dorabawila, Rosenberg.

Drafting of the manuscript: Dorabawila, Bassett, Rosenberg.

Critical revision of the manuscript for important intellectual content: Dorabawila, Hoefer, Bauer, Lutterloh, Rosenberg.

Statistical analysis: Dorabawila, Rosenberg.

Administrative, technical, or material support: Dorabawila, Bauer.

Supervision: Hoefer, Bauer, Bassett, Rosenberg.

Conflict of Interest Disclosures: None reported.

Additional Contributions: We acknowledge Jia Ren, MPH, Sofia Aronowitz, MPH, and Michele Boulais, MPH, New York State Department of Health (funded by the New York State Department of Health), for preliminary investigation; and Maya Sternberg, PhD, from the Centers for Disease Control and Prevention, for feedback on the eMethods in the Supplement. Dr Sternberg did not receive financial compensation for her contributions.