cdc.gov/coronavirus

Modeling Allocation Strategies for the Initial SARS-CoV-2 

Vaccine Supply 

Rachel B. Slayton, PhD, MPH

LCDR, USPHS

Data, Analytics, and Modeling Task Force

Advisory Committee on Immunization Practices 

Meeting

8/26/2020
Presentation Overview

 U.S. Population Stratification Model

 Nursing Home Model
Considerations for Mathematical Modeling

 Mathematical modeling is an iterative process 

 Models should be updated as new data become available 

 Sensitivity analyses enable systematic exploration of 

uncertainty 
U.S. Population Stratification Model
U.S. Population Stratification Model Methods

 Stratification based on National Health Interview Survey (NHIS) 2016-2018 

– Self-reported age, race/ethnicity, occupation, medical conditions

– Sample size 85,187 adults, 28,221 children (0-17 years old)

 Age groups:

– 0-17, 18-64, ≥65 years

 Race/ethnicity: 

– Non-Hispanic White

– Non-Hispanic Black

– Hispanic

– Other
U.S. Population Stratification Model Methods, Continued

 Risk Status (within each age group):

– Either 0 or ≥1 high-risk medical conditions

– NHIS-reported conditions: Obesity, chronic obstructive pulmonary 

disease (COPD), chronic cancer, weak/failing kidney, chronic heart 

problem, chronic diabetes

 Priority occupational groups: 

– Healthcare personnel (i.e., any individual working in a healthcare 

setting, paid or unpaid)

– Essential workers: food supply, emergency services, utilities, critical 

financial services, government, education
U.S. Population Stratification Model Methods, Continued

 Modeled a scenario including partial reopening and social distancing

– School contacts reduced by 70% from baseline

– Workplace contacts reduced by 50% from baseline (except for healthcare and 

essential workers)

 Assumed vaccine efficacy by age group per 2-dose course

– Analysis 1: 70% for persons 18-64 years old, 50% for persons ≥65 years old

– Analysis 2: 70% for persons 18-64 years old, 70% for persons ≥65 years old 

 Assumed immunity pre-vaccination 

– By age group: 0-17 years 2.8%, 18-64 7.9%, ≥65 years 4.4%

 Mortality 

– Unadjusted risk ratios by age, race/ethnicity and risk factors, adjusted to model 

strata by raking 
U.S. Population Stratification Model Methods, Continued

 Model considers incremental and relative impact of vaccination course

– Contact rates among the 72 strata in the model based on age and 

location structured contact rates (i.e., home, school, work, other) 

 Deterministic compartmental model framework

 Incremental impact estimated includes both direct and indirect benefits

– Assessed the impact on population-wide incidence 

– Derived from estimates of the rates of most probable transmission 

among groups before and after vaccination
Relative Impact from the U.S. Population Stratification 

Model: Analysis 1

Group vaccinated

Population -wide decrease in rate per 10 million courses

COVID-19 Infections COVID-19 Deaths

Healthcare personnel 3.5% 3.3%

Essential workers 3.1% 3.1%

With underlying conditions 3.8% 4.3%

Persons ≥65 years old 0.7% 6.1%

Vaccine Efficacy (VE) assumptions

 70% among persons 18-64 years old 

 50% among persons ≥65 years old
Relative Impact from the U.S. Population Stratification 

Model: Analysis 2

Group vaccinated

Population -wide decrease in rate per 10 million courses

COVID-19 Infections COVID-19 Deaths

Healthcare personnel 3.5% 3.4%

Essential workers 3.2% 3.2%

With underlying conditions 3.9% 4.8%

Persons ≥65 years old 1.0% 8.6%

Vaccine Efficacy (VE) assumptions

 70% among persons 18-64 years old 

 70% among persons ≥65 years old
Nursing Home Model
Nursing Home (NH) Model Overview

 Parametrized to mean nursing home characteristics from an analysis of 

Centers for Medicare & Medicaid Services (CMS) data

– 87 residents (mean length of stay 88 days)

– 41 healthcare personnel (HCP) who work in daily 8-hour shifts

 HCP interact at work with other HCP, and at home and in non-school 

settings with others in the community

 HCP self-isolate on symptom onset

 Prevalence of infection among admitted nursing home residents is assumed 

to follow community prevalence

 First vaccine dose is given before introduction of infection into a nursing 

home
Product Assumptions

 2 doses given 28 days apart

 Protection develops 14 days post-injection

 Vaccine Efficacy (VE) variable: 70%, 50%, 30% (among persons ≥65 years old)

 Assume that vaccination does not attenuate severity nor transmissibility of 

breakthrough infections

 Assume no waning of immunity over the analysis time horizon
SARS-CoV-2 Transmission Among Nursing Home Residents 

and Healthcare Staff Without Vaccination

Simulation of unmitigated outbreak in a typical skilled nursing facility
Potential Impact of Focused Vaccination at Nursing 

Homes

Residents assumed to be at higher risk of severe disease and death due to older age and presence of underlying conditions

 Vaccinating NH HCP 

results in greater 

reductions in both 

infections and deaths than 

vaccinating NH residents
Modeling Summary

 Vaccinating healthcare personnel, essential workers, or adults with underlying 

conditions resulted in reductions of COVID-19 infections and deaths

 Vaccinating adults ≥65 years old resulted in more modest declines in 

infections and larger declines in deaths

 Vaccinating nursing home healthcare personnel resulted in greater 

reductions in both infections and deaths than vaccinating nursing home 

residents
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TTY: 1-888-232-6348 www.cdc.gov

The findings and conclusions in this report are those of the authors and do not necessarily represent the 

official position of the Centers for Disease Control and Prevention.