Table 2.
Baseline cohort characteristics and model parameters for severe COVID-19 risk and vaccine effectiveness
| Cohort characteristics | Model input | Reference |
|---|---|---|
| Population size (N) | ||
| Each group | 1 million | |
| Group | ||
| Age group | 18–49, 50–64, 65–74, 75+ years | |
| Immune status | Immunocompetent, mild immunocompromised, moderate/severe immunocompromised | |
| Baseline vaccination status (%) | ||
| Boosted (1 dose) | 60% | 28 |
| Boosted (2+ doses) | 40% | |
| Seroprevalencea (%) | ||
| 18–49 years | 82.4% | 27 |
| 50–64 years | 65.8% | |
| 65–74 years | 46.8% | |
| 75+ years | 46.8% | |
| Severe COVID-19 monthly incidenceb (cases per 100,000 persons) | ||
| 18–49 years | 8 | 25 |
| 50–64 years | 16 | 25 |
| 65–74 years | 41 | 25 |
| 75+ years | 113 | 25 |
| Severe COVID-19 risk ratio for immunocompromised | ||
| Immunocompromised populations (all) | 2.8 | 25,29,32 |
| Relative vaccine effectiveness and waning over time (against infection and severe COVID-19) | ||
| Booster dose | Time-varying (See Appendix) | 1–4, 20, 30 |
aSeroprevalence estimated by nucleocapsid antibody to support history of natural infection, with adjustment for number of infections since the last survey to approximate September 2022.
bIncidence estimates for severe COVID-19 (defined by hospitalization or death) were generated using publicly available US CDC data, averaging over 6 months preceding September 2022, coinciding with introduction of the bivalent vaccine.
See Appendix for further methodologic description.