Morbidity and Mortality Weekly Report

Outbreak of SARS-CoV-2 B.1.617.2 (Delta) Variant Infections Among
Incarcerated Persons in a Federal Prison — Texas, July–August 2021
Liesl M. Hagan, MPH1*; David W. McCormick, MD1,2*; Christine Lee, PhD1; Sadia Sleweon, MPH1; Lavinia Nicolae, PhD1; Thomas Dixon3;
Robert Banta, MSN3; Isaac Ogle, MSN3; Cristen Young3; Charles Dusseau3; Shawn Salmonson3; Charles Ogden, MPH3; Eric Godwin3;
TeCora Ballom, DO3; Tara Ross3; Hannah Browne1; Jennifer L. Harcourt, PhD1; Azaibi Tamin, PhD1; Natalie J. Thornburg, PhD1;
Hannah L. Kirking, MD1; Phillip P. Salvatore, PhD1; Jacqueline E. Tate, PhD1

On September 21, 2021, this report was posted as an MMWR
Early Release on the MMWR website (https://www.cdc.gov/mmwr).
Incarcerated populations have experienced disproportionately higher rates of COVID-19–related illness and death
compared with the general U.S. population, due in part to
congregate living environments that can facilitate rapid transmission of SARS-CoV-2, the virus that causes COVID-19,
and the high prevalence of underlying medical conditions
associated with severe COVID-19 (1,2). The SARS-CoV-2
B.1.617.2 (Delta) variant has caused outbreaks among vaccinated and unvaccinated persons in congregate settings and
large public gatherings (3,4). During July 2021, a COVID-19
outbreak involving the Delta variant was identified in a federal prison in Texas, infecting 172 of 233 (74%) incarcerated
persons in two housing units. The Federal Bureau of Prisons
(BOP) partnered with CDC to investigate. CDC analyzed data
on infection status, symptom onset date, hospitalizations, and
deaths among incarcerated persons. The attack rate was higher
among unvaccinated versus fully vaccinated persons (39 of 42,
93% versus 129 of 185, 70%; p = 0.002).† Four persons were
hospitalized, three of whom were unvaccinated, and one person
died, who was unvaccinated. Among a subset of 70 persons
consenting to an embedded serial swabbing protocol, the
median interval between symptom onset and last positive
reverse transcription–polymerase chain reaction (RT-PCR) test
result in fully vaccinated versus unvaccinated persons was similar (9 versus 11 days, p = 0.37). One or more specimens were
culture-positive from five of 12 (42%) unvaccinated and 14 of
37 (38%) fully vaccinated persons for whom viral culture was
attempted. In settings where physical distancing is challenging, including correctional and detention facilities, vaccination
and implementation of multicomponent prevention strategies
* These authors contributed equally to the report.
† All persons included in the vaccine coverage calculation categorized as vaccinated
were fully vaccinated. Persons were considered fully vaccinated if ≥14 days had
elapsed since they completed all recommended doses of a Food and Drug
Administration (FDA)-authorized COVID-19 vaccine series before symptom
onset or date of first positive test. Persons were considered partially vaccinated
if they had not completed all doses of an FDA-authorized COVID-19 vaccine
series or if they had received the final vaccine dose <14 days before symptom
onset or date of first positive test. Partially vaccinated persons were excluded
from statistical comparisons by vaccination status.

(e.g., testing, medical isolation, quarantine, and masking) are
critical to limiting SARS-CoV-2 transmission (5).

Investigation and Response
On July 12, 2021, 18 persons incarcerated in a federal prison
in Texas reported COVID-19–like symptoms to BOP health
services staff members. All 18 received positive SARS-CoV-2
test results using the Abbott BinaxNOW COVID-19 Ag
Card (rapid antigen) test; 11 were fully vaccinated. Three of
these persons had reported to the on-site clinic on July 8 with
symptoms including coryza, cough, headache, myalgia, or
rhinorrhea but did not receive SARS-CoV-2 testing at that
time.§ The 18 persons with positive test results lived in two
interconnected units (unit A and unit B) that operated as a
single cohort and housed 233 persons in 2- to 10-person cells
without doors. Standard COVID-19 prevention protocols that
were in place among incarcerated persons included mandatory
masking in common areas, cohorting of housing units for daily
activities, and head-to-toe sleeping arrangements. Among staff
members, prevention protocols included mandatory masking
and mandatory daily COVID-19 symptom screening and temperature checks (5).¶ Before the outbreak, incarcerated persons
moved freely between units A and B and were together for meals,
recreation, and work; they did not have contact with incarcerated persons housed in other units. After initial identification of
COVID-19 cases, unit A was designated as a quarantine unit for
persons with negative test results, and unit B was designated as
§ These persons were identified by a review of on-site clinic records. Clinic records

and discussions with on-site staff members suggested that clinicians thought
symptoms were likely due to other causes, given a lack of known cases in the
prison since January 2021.
¶ Alcohol-based hand sanitizer was provided in staff-only areas. Mitigation
measures among incarcerated persons beyond mandatory masking in common
areas included on-site voluntary vaccination provided by BOP; prompt medical
isolation of persons testing positive for SARS-CoV-2 and quarantine of exposed
persons testing negative; consistent cohorting of housing units for daily activities
including meals, recreation, and work assignments; and head-to-toe sleeping
arrangements. Signs encouraging frequent hand hygiene were posted throughout
the prison, and soap was provided without cost to incarcerated persons.
Environmental mitigation measures included regular disinfection of common
areas and high-touch surfaces and provision of individual bottles of disinfectant
to incarcerated persons for use in their personal spaces. Hard plastic barriers
were installed in visitation areas to prevent physical contact between incarcerated
persons and visitors.

US Department of Health and Human Services/Centers for Disease Control and Prevention

MMWR / September 24, 2021 / Vol. 70 / No. 38

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Morbidity and Mortality Weekly Report

a medical isolation unit for COVID-19 patients. Staff members
assigned to units A and B rotated between these two units and to
other units on the basis of daily staffing needs.
During July 12–August 14, 2021, BOP staff members offered
same-day SARS-CoV-2 rapid antigen testing to all 233 persons
in units A and B reporting symptoms or known exposures; the
entire quarantined cohort received testing from BOP during
July 12–13 and again on July 14, July 19, July 22, August 2, and
August 10 with a combination of rapid antigen and RT-PCR
tests.** SARS-CoV-2 testing among staff members was voluntary and was performed off-site by staff members’ health
care providers. A subset of 70 incarcerated persons in units A
and B consented to a secondary investigation for which they
reported symptom data through a questionnaire and provided
nasal midturbinate swabs daily for up to 20 days after symptom
onset. Specimens were tested by RT-PCR.†† Viral culture was
attempted for RT-PCR–positive specimens from a nonrandom
subset of participants.§§ Genomic sequencing was attempted
for one RT-PCR–positive specimen from each participant,
when possible.
COVID-19 vaccination was voluntary for BOP staff and
incarcerated persons. In 2020, BOP worked with CDC to
develop a vaccine prioritization plan in which all staff members
were offered vaccination first, followed by incarcerated persons.
Among incarcerated persons, those aged ≥65 years and those
with underlying medical conditions associated with severe
COVID-19 were the first to receive a COVID-19 vaccine. In
this prison, the Pfizer-BioNTech vaccine was the first available, with first doses administered to incarcerated persons in
January 2021.¶¶ Staff vaccination coverage in this report includes
only doses administered as part of the BOP occupational health
program. BOP was unable to determine the number of staff
members who were vaccinated through other providers.
Information on vaccination, demographic characteristics, and
underlying medical conditions was extracted from BOP electronic medical records for all 233 persons living in units A and B.
Demographic characteristics, underlying medical conditions, and
COVID-19–associated hospitalizations and deaths were compared
by vaccination status and, among vaccinated persons, by vaccine
** Rapid antigen testing was used during the early and middle phases of the
outbreak to identify cases quickly and facilitate timely separation of infected
persons from those with negative test results. RT-PCR testing was used in the
late phase of the outbreak to confirm no new cases had occurred before lifting
quarantine precautions.
†† https://www.fda.gov/media/139743/download
§§ RT-PCR–positive specimens were chosen for viral culture to include both
vaccinated and unvaccinated participants and to represent different points in
time since first positive diagnostic test. All specimens chosen for culture from
vaccinated and unvaccinated participants had a cycle threshold value of <38
and were collected from 3 days before through 13 days after symptom onset.
¶¶ h t t p s : / / w w w . s c i e n c e d i r e c t . c o m / s c i e n c e / a r t i c l e / p i i
S0264410X21010781?via%3Dihub

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MMWR / September 24, 2021 / Vol. 70 / No. 38

product received. Attack rates were compared by demographic and
medical characteristics, vaccination status and vaccine product,
and time since vaccination. Descriptive statistics were calculated.
Differences between groups were assessed using chi-square or Fisher’s
exact tests. P-values <0.05 were considered statistically significant,
adjusted for multiple comparisons using the Bonferroni correction
method. Statistical analyses were performed using SAS (version 9.4;
SAS Institute). This activity was reviewed and approved by the BOP
Research Review Board and CDC and conducted consistent with
applicable federal law and CDC policy.***
Among 233 incarcerated persons, 185 (79%) of whom were
fully vaccinated, 172 (74%) received positive SARS-CoV-2
test results during July 12–August 14 (Supplementary Figure,
https://stacks.cdc.gov/view/cdc/109901). Among a subset of
70 symptomatic persons providing swabs for serial testing,
no significant difference was found in the median interval
between reported symptom onset and last positive RT-PCR
result in vaccinated versus unvaccinated persons (9 versus 11
days, respectively; p = 0.37) (Figure). Virus was cultured from
one or more specimens from five of 12 (42%) unvaccinated
and 14 of 37 (38%) fully vaccinated persons for whom viral
culture was attempted. Genomic sequencing confirmed the
AY.3 sublineage of the Delta variant in 58 specimens from
58 persons.
Vaccination coverage was 79% among incarcerated persons
in units A and B. Among fully vaccinated persons, 93 of 122
(76%) Pfizer-BioNTech recipients and 0 of 50 (0%) Moderna
recipients had been vaccinated ≥4 months before the outbreak
(p<0.001). A larger proportion of Pfizer-BioNTech recipients
had diabetes (p = 0.02) or hypertension (p<0.001) than Moderna
or Janssen COVID-19 vaccine recipients, and a higher proportion of Pfizer-BioNTech and Janssen recipients had a history of
smoking (p<0.001) than Moderna recipients (Table 1).
Attack rates were higher among unvaccinated persons (39 of
42; 93%) than among fully vaccinated persons (129 of 185;
70%) (p = 0. 002) and among persons vaccinated ≥4 months
before the outbreak (83 of 93; 89%) than among those vaccinated 2 weeks to 2 months before the outbreak (19 of 31; 61%)
(p<0.001) (Table 2).
Among both persons with and without a previous
SARS-CoV-2 infection, the attack rate was lower among
fully vaccinated versus unvaccinated persons (1 of 21 [5%]
versus 4 of 7 [57%], p = 0.008; 128 of 164 [78%] versus 35
of 35 [100%], p<0.001) (Supplementary Table, https://stacks.
cdc.gov/view/cdc/109901). Among fully vaccinated persons
without a previous SARS-CoV-2 infection, the attack rate was
*** 45 C.F.R. part 46, 21 C.F.R. part 56; 42 U.S.C. Sect. 241(d); 5 U.S.C. Sect.
552a; 44 U.S.C. Sect. 3501 et seq.

US Department of Health and Human Services/Centers for Disease Control and Prevention

h Options
ide = 7.5”
tats = 5.0”
mns = 4.65”
mn = 3.57”

Morbidity and Mortality Weekly Report

FIGURE. Number of days* between COVID-19 symptom onset and
last positive SARS-CoV-2 reverse transcription–polymerase chain
reaction test result among incarcerated persons† in a federal prison,
by vaccination status§ — Texas, July 19–August 9, 2021

•

Fully vaccinated (N = 60)
0 Unvaccinated (N = 10)

Vaccinated

• • 1

1!tf1i1!··

. +

Unvaccinated

I

0

I

2

I

4

.
I

6

I .. t

8
I

8

I

10

I

12

I

14

•
I

16

I

18

I

20

No. of days between symptom
onset and last positive test
Abbreviation: FDA = Food and Drug Administration.
* Vertical lines indicate median number of days; horizontal lines indicate
interquartile ranges.
† A subset of 70 persons who consented to an embedded serial swabbing protocol.
§ Persons were considered fully vaccinated if ≥14 days had elapsed since they
completed all recommended doses of an FDA-authorized COVID-19 vaccine
series before symptom onset or date of first positive test.

higher among Pfizer-BioNTech recipients (99 of 117; 85%)
than among Moderna recipients (19 of 35; 54%) (p<0.001).
Among 172 infected persons, four (2%) were hospitalized for
COVID-19, including three (8%) of 39 unvaccinated patients,
and one (1%) of 129 fully vaccinated patients (p = 0.04).
One (3%) of the unvaccinated hospitalized patients required
endotracheal intubation and mechanical ventilation and died
in the hospital (Table 1).†††
Nine of 275 (3%) staff members, four of whom worked in units A
or B, reported a positive SARS-CoV-2 test result during the outbreak
and were restricted from work per BOP policy. BOP administered
COVID-19 vaccine to 37% of staff members in the prison.
Discussion

This study demonstrates the potential for SARS-CoV-2 Delta
variant outbreaks in congregate settings including correctional
and detention facilities, even among resident populations with
†††

The unvaccinated hospitalized patient who died was aged 50–59 years and
had obesity, hypertension, and a history of smoking. Among the remaining
two hospitalized unvaccinated patients, one was aged 40–49 years and had
obesity, and the other was aged 40–49 years and had overweight and moderate
to severe asthma. The vaccinated hospitalized patient was aged 50–59 years
and had obesity, type II diabetes, hypertension, and a history of smoking.

high vaccination coverage. In this outbreak involving almost
three fourths of the incarcerated population in the affected housing units, fewer hospitalizations and deaths occurred among
vaccinated than unvaccinated persons, highlighting vaccination
as an important strategy to reduce serious COVID-19–related
illness and death in congregate settings. In addition, the high
number of infections in vaccinated persons, comparable duration
of positive RT-PCR test results after symptom onset regardless of
vaccination status, and presence of infectious virus in specimens
from both unvaccinated and vaccinated infected persons underscore the importance of implementing and maintaining multiple
COVID-19 prevention strategies in settings where physical distancing is challenging, even when vaccination coverage is high.
Prevention strategies that were in place during this outbreak,
including promptly separating infected and exposed persons and
cohorting housing units for daily activities, might have prevented
the outbreak from spreading to other areas of the prison.
Three of the four hospitalizations and the only death
occurred in unvaccinated persons. These findings are consistent
with a previous study in which vaccination with a COVID-19
mRNA vaccine (Pfizer-BioNTech or Moderna) reduced the risk
for hospitalization associated with Delta variant infection (6).
These findings reinforce the critical importance of vaccination
in reducing risk for severe illness and death from SARS-CoV-2
Delta variant infections, particularly in congregate settings.
Natural infection with SARS-CoV-2 confers some degree of
immunity, although the duration of protection is unknown (7).
In this outbreak, the lowest attack rate occurred among fully vaccinated persons with previous infection, highlighting the importance
of vaccination, even among persons with previous infection. In
addition, attack rates in persons without previous infection were
higher among Pfizer-BioNTech recipients than among Moderna
recipients. In a recent study, the Moderna vaccine was found to be
more effective at preventing COVID-19–related hospitalizations
among U.S. adults without immunocompromising conditions
(6). In this outbreak, attack rates were also higher in persons who
were vaccinated ≥4 months before the outbreak compared with
persons vaccinated more recently. Because all persons vaccinated
≥4 months before the outbreak received the Pfizer-BioNTech
vaccine, determining the independent impact of vaccine product
versus time since vaccination was not possible. Additional research
is warranted to assess the duration of vaccine-induced and natural
immunity, as well as the duration of infectious virus shedding by
vaccinated and unvaccinated infected persons.
BOP records indicate that nearly two thirds of staff members
in this prison were unvaccinated, and at least nine were infected
during this outbreak. In addition, during the 2 weeks before the

US Department of Health and Human Services/Centers for Disease Control and Prevention

MMWR / September 24, 2021 / Vol. 70 / No. 38

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Morbidity and Mortality Weekly Report

TABLE 1. Vaccination status* among incarcerated persons in a federal
prison, by demographic characteristics, underlying conditions, and
COVID-19–associated hospitalizations and deaths — Texas,
July 12–August 14, 2021

TABLE 1. (Continued) Vaccination status* among incarcerated persons
in a federal prison, by demographic characteristics, underlying
conditions, and COVID-19–associated hospitalizations and deaths —
Texas, July 12–August 14, 2021

No. (%)
Characteristic

Total

Fully
Unvaccinated vaccinated

No. (%)
p-value†

Total
233 (100)
42 (18)
185 (79)
—
Sex
Male
233 (100)
42 (18)
185 (79)
—
Age group, yrs
—
—
—
0.17
18–29 (Ref.)
10 (4)
3 (33)
6 (67)
Ref.
30–39
63 (27)
16 (26)
46 (74)
0.69
40–49
68 (29)
11 (17)
53 (83)
0.36
50–59
65 (28)
10 (15)
55 (85)
0.19
≥60
27 (12)
2 (7)
25 (93)
0.09
Race/Ethnicity
—
—
—
0.02
American Indian/
5 (2)
0 (—)
5 (100)
1.0
Alaska Native
Asian
3 (1)
0 (—)
2 (100)
1.0
Black, non-Hispanic
47 (20)
16 (36)
29 (64)
<0.001§
Hispanic
34 (15)
7 (22)
25 (78)
0.22
White, non-Hispanic
144 (62)
19 (13)
124 (87)
Ref.
Country of birth
Outside the
10 (4)
3 (33)
6 (67)
United States
0.37
United States
223 (96)
39 (18)
179 (82)
Vaccination status
Fully vaccinated
185 (79)
—
185 (100)
—
Partially vaccinated
6 (3)
—
—
Unvaccinated
42 (18)
42 (100)
—
Vaccine product received (among fully vaccinated)
Janssen
—
—
13 (100)
—
(Johnson & Johnson)
Moderna
—
—
50 (100)
Pfizer-BioNTech
—
—
122 (100)
Time from full vaccination to outbreak (among fully vaccinated)
≥2 wks to 2 mos
—
—
31 (100)
2–4 mos
—
—
61 (100)
—
4–6 mos
—
—
93 (100)
Documented previous SARS-CoV-2 infection
No
204 (88)
35 (18)
164 (82)
0.34
Yes
29 (12)
7 (25)
21 (75)
Housing unit before outbreak
A
146 (63)
25 (18)
116 (82)
0.70
B
87 (37)
17 (20)
69 (80)

outbreak, community transmission was high.§§§ SARS-CoV-2
can be introduced into correctional facility populations and
back into the community through daily entry and exit of staff
members and interfacility transfers of incarcerated persons, and
the identification of a single viral lineage among all sequenced
§§§

https://www.cdc.gov/coronavirus/2019-ncov/covid-data/covidview/index.
html. CDC defines community transmission as high when ≥10.0% of nucleic
acid amplification tests (NAATs) in the previous 7 days have been positive
or when ≥100 new cases per 100,000 persons have occurred in the previous
7 days. In the 2 weeks before the outbreak described in this report, median
NAAT test positivity was 17.8% (range = 5%–39.5%) in counties
surrounding the affected federal prison.

1352

MMWR / September 24, 2021 / Vol. 70 / No. 38

Characteristic

Total

Fully
Unvaccinated vaccinated

Underlying medical conditions¶
History of smoking**
121 (52)
Overweight††
89 (38)
Obesity††
101 (43)
Severe obesity††
19 (8)
Hypertension
90 (39)
Diabetes
29 (12)
Moderate to
25 (11)
severe asthma
Chronic obstructive
16 (7)
pulmonary disease
Immunocompromised
4 (2)
state
Chronic kidney disease
3 (1)
Cancer
2 (1)
Liver disease
2 (1)
Serious cardiac
1 (0)
condition
HIV infection
1 (0)
COVID-19 outcomes
Hospitalization
4 (2)
Death
1 (0)

p-value†
0.006§

14 (12)
22 (25)
13 (13)
1 (6)
13 (15)
2 (7)
3 (12)

105 (88)
66 (75)
84 (87)
17 (94)
75 (85)
27 (93)
21 (88)

1 (7)

14 (93)

0.32

0 (—)

4 (100)

1.0

0 (—)
0 (—)
1 (50)
1 (0)

3 (100)
2 (100)
1 (50)
0 (—)

1.0
1.0
0.34
0.19

0 (—)

1 (100)

1.0

3 (75)
1 (100)

1 (25)
0 (—)

0.07
0.25
0.12
0.58

0.04§
0.23

Abbreviations: BMI = body mass index; FDA = Food and Drug Administration;
Ref. = referent group.
* Descriptive statistics were not calculated for partially vaccinated persons. Partially
vaccinated persons were excluded from statistical comparisons by vaccination
status. Persons were considered fully vaccinated if ≥14 days had elapsed since
they completed all recommended doses of an FDA-authorized COVID-19 vaccine
series before symptom onset or date of first positive test. Persons were considered
partially vaccinated if they had not completed all doses of an FDA-authorized
COVID-19 vaccine series or if they had received the final vaccine dose <14 days
before symptom onset or date of first positive test.
† P-values from chi-square test (when all cell sizes ≥5) or Fisher’s exact test
(when any cell size <5).
§ Statistically significant difference; p-values <0.05 were considered
statistically significant, adjusted for multiple comparisons using the
Bonferroni correction method.
¶ No persons had pulmonary fibrosis or history of solid organ or stem
cell transplant.
** Information on the type of product smoked was not available.
†† Overweight: BMI >25 kg/m2 but <30 kg/m2; obesity: BMI ≥30 kg/m2 but
<40 kg/m2; severe obesity: BMI ≥40 kg/m2.

specimens in this outbreak suggests a single introduction
of the virus into the prison (8). Bidirectional connections
between correctional facilities and communities highlight the
importance of high vaccination coverage among both staff
members and incarcerated persons, early diagnostic testing,
routine screening testing when community transmission is
high, maintaining consistent assignments of staff members for
each housing unit, and excluding staff members from work
when they are symptomatic or have COVID-19 (5,9).
The findings in this report are subject to at least five limitations. First, although rapid antigen testing can identify cases

US Department of Health and Human Services/Centers for Disease Control and Prevention

Morbidity and Mortality Weekly Report

TABLE 2. SARS-CoV-2 attack rates among incarcerated persons in a
federal prison, by demographic characteristics, vaccination status,
COVID-19 vaccine product, and underlying conditions — Texas,
July 12–August 14, 2021
Characteristic

Total
(column %)

No. of
cases

Attack
rate, %

Total
233 (100)
172
74
Vaccination status†
—
—
—
Unvaccinated
42 (18)
39
93
Partially vaccinated
6 (3)
4
67
Fully vaccinated
185 (79)
129
70
Vaccine product
—
—
—
(among fully
vaccinated)
Janssen
13 (7)
10
77
(Johnson & Johnson)
Moderna
50 (27)
20
40
Pfizer-BioNTech
122 (66)
99
81
Time from full vaccination to outbreak (among fully
vaccinated)
≥2 wks to 2 mos
31 (17)
19
61
2–4 mos
61 (33)
27
44
4–6 mos
93 (50)
83
89
Sex
Male
233 (100)
172
74
Age group, yrs
—
—
—
18–29
10 (4)
6
60
30–39
63 (27)
43
68
40–49
68 (29)
50
74
50–59
65 (28)
52
80
≥60
27 (12)
21
78
Race/Ethnicity
—
—
—
American Indian/
5 (2)
3
60
Alaska Native
Asian
3 (1)
3
100
Black, non-Hispanic
47 (20)
31
66
Hispanic
34 (15)
22
65
White, non-Hispanic
144 (62)
113
78
Country of birth
Outside United States
10 (4)
9
90
United States
223 (96)
163
73
Housing unit before outbreak
Unit A
146 (63)
107
73
Unit B
87 (37)
65
75

p-value*
—
0.003§
0.002§
1.0
Ref.
<0.001§
0.03
Ref.
<0.001§
<0.001§
Ref.
0.12
<0.001§
—
0.46
Ref.
0.72
0.46
0.22
0.41
0.16
0.31
1.0
0.08
0.09
Ref.
0.46

0.81

quickly, its limited sensitivity for detecting infections in asymptomatic patients can underestimate attack rates (10). Second,
transmission might have preceded initial identification of cases,
resulting in an underestimation of total cases. Third, it is uncertain whether lower attack rates by vaccine product were caused
by differences in waning vaccine-induced immunity, varying
levels of protection among vaccine products, or differences in
exposure level among persons who received different vaccine
products. Fourth, testing was not mandatory for BOP staff
members, limiting the ability to confirm the total numbers
of COVID-19 cases. Finally, RT-PCR–positive specimens
were not selected randomly for viral culture and thus are not
representative of all vaccinated and unvaccinated participants.

TABLE 2. (Continued) SARS-CoV-2 attack rates among incarcerated
persons in a federal prison, by demographic characteristics,
vaccination status, COVID-19 vaccine product, and underlying
conditions — Texas, July 12–August 14, 2021
Characteristic

Total
(column %)

Underlying medical conditions
History of smoking¶
121 (52)
Hypertension
90 (39)
Overweight**
89 (38)
Obesity**
101 (43)
Severe obesity**
19 (8)
Moderate to severe
25 (11)
asthma
Diabetes
29 (12)
Chronic obstructive
16 (7)
pulmonary disease
Chronic kidney disease
3 (1)
Immunocompromised
4 (2)
state
Liver disease
2 (1)
Cancer
2 (1)
Serious cardiac
1 (0.4)
condition
HIV infection
1 (0.4)

No. of
cases

Attack
rate, %

88
73
64
76
16
21

73
81
72
75
84
84

0.34

26
15

90
94

0.04§
0.08

3
3

100
75

0.57
1.0

2
1
1

100
50
100

1.0
0.46
1.0

1

100

1.0

p-value*
0.69
0.05
0.55

Abbreviations: BMI = body mass index; FDA = Food and Drug Administration;
Ref. = referent group.
* P-values from chi-square test (when all cell sizes ≥5) or Fisher’s exact test
(when any cell size <5).
† Persons were considered fully vaccinated if ≥14 days had elapsed since they
completed all recommended doses of an FDA-authorized COVID-19 vaccine
series before symptom onset or date of first positive test. Persons were
considered partially vaccinated if they had not completed all doses of an
FDA-authorized COVID-19 vaccine series or if they had received the final
vaccine dose <14 days before symptom onset or date of first positive test.
§ Statistically significant difference; p-values <0.05 were considered
statistically significant, adjusted for multiple comparisons using the
Bonferroni correction method.
¶ Information on type of product smoked was not available.
** Overweight: BMI >25 kg/m2 but <30 kg/m2; obesity: BMI ≥30 kg/m2 but
<40 kg/m2; severe obesity: BMI ≥40 kg/m2.

During a COVID-19 outbreak in a federal prison involving
the highly transmissible SARS-CoV-2 Delta variant, transmission was high among vaccinated and unvaccinated persons.
Although hospitalizations, deaths, and attack rates were higher
among unvaccinated than vaccinated persons, the duration of
positive serial test results was similar between these two groups,
and infectious virus was cultured from both vaccinated and
unvaccinated participants. Widespread vaccination among incarcerated persons and staff members in coordination with other
prevention strategies, including early diagnostic testing for all
persons with any COVID-19–like symptoms, screening testing,
medical isolation, quarantine, masking, and physical distancing
where possible, remain critical to limiting SARS-CoV-2 transmission and COVID-19–related illness and death in congregate
settings, including correctional and detention facilities (5).

US Department of Health and Human Services/Centers for Disease Control and Prevention

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Morbidity and Mortality Weekly Report

References

Summary
What is already known about this topic?
Incarcerated populations have experienced disproportionately
higher rates of COVID-19–related illness and death.
What is added by this report?
During a COVID-19 outbreak involving the Delta variant in a
highly vaccinated incarcerated population, transmission rates
were high, even among vaccinated persons. Although attack
rates, hospitalizations, and deaths were higher among unvaccinated than among vaccinated persons, duration of positive
serial test results was similar for both groups. Infectious virus
was cultured from vaccinated and unvaccinated infected
persons.
What are the implications for public health practice?
Even with high vaccination rates, maintaining multicomponent
prevention strategies (e.g., testing and masking for all persons
and prompt medical isolation and quarantine for incarcerated
persons) remains critical to limiting SARS-CoV-2 transmission in
congregate settings where physical distancing is challenging.

Acknowledgments
Mario Cordova, Torrey Haskins, Jennifer Jackson, Joshua Jett,
Barbara Swopes, Tammy Winbush, Federal Bureau of Prisons; Raydel
Anderson, Adam K. Wharton, Kay W. Radford, Gimin Kim, Dexter
Thompson, Benton Lawson, Congrong Miao, Bettina Bankamp,
Suganthi Suppiah, Michael Bowen, Baoming Jiang, Jan Vinjé, Amy
Hopkins, Kenny Nguyen, Leslie Barclay, Sung-Sil Moon, Leeann
Smart, Courtnee Wright, Mary Casey-Moore, Boris Relja, Michelle
Honeywood, Rashi Gautam, Theresa Bessey, Jennifer M. Folster,
Shannon Rogers, Nhien T. Wynn, John Michael Metz, Ebenezer David,
Madina Jumabaeva, Justin Runac, Min-shin Chen, Maria Solano,
Joyce Peterson, Diagnostics Testing Laboratories, CDC COVID-19
Response Team; Dhwani Batra, Andrew Beck, Jason Caravas, Victoria
Caban-Figueroa, Eric Chirtel, Roxana Cintron-Moret, Peter W. Cook,
Jonathan Gerhart, Christopher Gulvik, Norman Hassell, Dakota
Howard, Yunho Jang, Tymeckia Kendall, Rebecca J. Kondor, Nicholas
Kovacs, Kristine Lacek, Brian R. Mann, Laura K. McMullan, Kara
Moser, Roopa Nagilla, Clinton R. Paden, Benjamin Rambo-Martin,
Adam Retchless, Matthew Schmerer, Sandra Seby, Samuel Shepard,
Phillip Shirk, Catherine Smith, Richard Stanton, Thomas Stark, Erisa
Sula, Yvette Unoarumhi, Xiao-yu Zheng, Jonathan Zhong, CDC Strain
Surveillance and Emerging Variant Work Group.

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Corresponding author: Liesl M. Hagan, vqf8@cdc.gov.
1CDC COVID-19 Response Team; 2Epidemic
3Bureau of Prisons, U.S. Department of Justice.

Intelligence Service, CDC;

All authors have completed and submitted the International
Committee of Medical Journal Editors form for disclosure of potential
conflicts of interest. No potential conflicts of interest were disclosed.

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US Department of Health and Human Services/Centers for Disease Control and Prevention