cdc.gov/coronavirus

Modeling the Potential Impact of Vaccination Strategies for 

Nursing Home Residents and Staff

Rachel B. Slayton, PhD, MPH

LCDR, U.S. Public Health Service

Epidemiology Taskforce, Modeling Team

September 22, 2021
Model overview
Weekly rate of COVID-19 cases in communities and in nursing 

homes
Methods

Overview

 Model nursing home (NH): 

• 100 staff, 100 residents 

• Assumed 100% occupancy

• Resident turnover explicitly modeled

 Staff: daily probability of infection from community (NHSN)

 Transmission within the nursing home:

• Stochastic, based on the probability of transmission 

given contact, no. contacts per day, and total no. of 

infected individuals

 Non-outbreak screening testing of unvaccinated staff

• Twice per week (per guidelines in high community 

transmission settings)

Outcomes

 Total number of both infections and symptomatic cases in:

 Residents and entire NH (residents and staff)

 Over 2 months

 Results: 100 simulations

Extension of model: doi/10.1093/cid/ciab517/6292250

Parameter Values

R0 6 (Delta 

estimate)

Staff daily probability of community infection 0.001 - 0.003 

(NHSN)

Resident vaccination coverage 80%

Staff vaccination coverage 40% - 100%

2 dose vaccine efficacy (VE) against infection 

(staff)

70%

2 dose VE against infection (residents) 50% - 70%

2 dose VE against symptomatic disease(staff) 90%

2 dose VE against symptomatic disease 

(residents)

80% - 90%

VE against infectiousness (residents and staff) 50%

Booster dose VE against infection (residents, 

takes 2 weeks to take effect)

60% - 90%
50% 2

-dose 

VE against 

infection 

(residents)

Cumulative COVID-19 

incidence among residents 

after 2 months by symptom 

status (shading) and 

vaccination status (color) 

for 100 simulations

Resident coverage: 80%

Staff coverage: 60%

No boosters

Most cases in vaccinated 

residents are asymptomatic due 

to VE against symptomatic 

disease

While only 20% of residents 

areunvaccinated, they contribute a large share of symptomatic 

cases

Higher daily importation rate 

from community  more NH 

cases ● Increase in NH cases does 

not necessarily indicate 

lower or waning VE if 

community transmission is 

rising
50% 2

-dose 

VE against 

infection 

(residents)

70% 2-dose 

VE against 

infection 

(residents)

Cumulative COVID-19 

incidence among residents 

after 2 months by symptom 

status (shading) and 

vaccination status (color) 

for 100 simulations

Resident coverage: 80%

Staff coverage: 60%

No boosters

Most cases in vaccinated 

residents are asymptomatic due 

to VE against symptomatic 

disease

While only 20% of residents 

areunvaccinated, they contribute a large share of symptomatic 

cases

Higher daily importation rate 

from community  more NH 

cases ● Increase in NH cases does 

not necessarily indicate 

lower or waning VE if 

community transmission is 

rising
Assessing the impact of varying levels of staff 

COVID-19 vaccination coverage and providing all 

vaccinated residents a booster dose
Symptomatic COVID-19 cases among residents

• 217 unique residents in nursing 

home over 2 months

• Median duration of a nursing 

home stay is27 days

Findings

• Higher staff vaccination 

coverage (top rows) leads to 

fewer symptomatic cases • Cumulative cases highly 

dependent on community 

transmission rate (left vs. right 

panel)
Symptomatic COVID-19 cases among residents

Average vaccination coverage in U.S. nursing home staff: ~60%

• 217 unique residents in nursing 

home over 2 months

• Median duration of a nursing 

home stay is 27 days

Findings

• Higher staff vaccination 

coverage (top rows) leads to 

fewer symptomatic cases • Cumulative cases highly 

dependent on community 

transmission rate (left vs. right 

panel
Symptomatic COVID-19 cases among residents

• 217 unique residents in nursing 

home over 2 months

• Median duration of a nursing 

home stay is27 days

Findings

• Higher staff coverage and 

higher booster VE (top right) 

leads to fewer symptomatic 

cases • Cumulative cases highly 

dependent on community 

transmission rate (left vs. right 

panel)
Total symptomatic and asymptomatic COVID-19 infections 

among residents

Findings

• There are higher numbers of 

infections when looking at 

total infections (symptomatic 

and asymptomatic) 

compared to symptomatic 

cases only.

Trends remain the same:

• Higher staff coverage and 

higher booster VE (top right) 

leads to fewer infections • Cumulative cases highly 

dependent on community 

transmission rate (left vs. right 

panel)
Symptomatic COVID-19 cases in nursing home (residents and 

staff)

Findings

• Similar trends when looking 

at all symptomatic cases in NH 

(residents and staff) as in 

residents only

• This shows a larger impact of 

increasing staff coverage due 

to direct protection for staff
Total COVID-19 infections (symptomatic and asymptomatic) 

in nursing home (residents and staff)

Findings

• Similar trends when looking at 

all total infections in NH 

(residents and staff) as in 

residents only

• There are higher numbers 

of infections when looking at 

total infections (symptomatic 

and asymptomatic) 

compared to symptomatic 

cases only

• This shows a larger impact of 

increasing staff coverage due 

to direct protection for staff
Limitations

 We modeled VE against infection, VE against symptomatic disease, and VE 

against infectiousness as point estimates

– These estimates may vary (e.g., by vaccine type, age of vaccinated 

persons, immunocompromising conditions of vaccinated persons)

 We modeled an average nursing home and did not capture all facility-level 

heterogeneity

 Previous COVID-19 infections are not modeled which may underestimate 

the level of prior immune protection

 We do not explore the impact of vaccine supply shortages in this model
Summary

• Maximizing COVID-19 vaccination coverage among staff remains a critical 

tool for preventing cases in nursing homes

• Boosters for nursing home residents can help reduce cases

• Magnitude of their effect depends on their effectiveness and staff 

vaccine coverage

• Even with highly effective boosters, cases in nursing homes will 

persist when community transmission is high, highlighting the need 

for continued infection prevention and control strategies

• Community transmission remains a key driver of cases in nursing homes
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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.