Residents of long-term care facilities (LTCFs), particularly those in skilled nursing
facilities (SNFs), have experienced disproportionately high levels of COVID-19–associated
morbidity and mortality and were prioritized for early COVID-19 vaccination (
1
,
2
). However, this group was not included in COVID-19 vaccine clinical trials, and limited
postauthorization vaccine effectiveness (VE) data are available for this critical
population (
3
). It is not known how well COVID-19 vaccines protect SNF residents, who typically
are more medically frail, are older, and have more underlying medical conditions than
the general population (
1
). In addition, immunogenicity of the Pfizer-BioNTech vaccine was found to be lower
in adults aged 65–85 years than in younger adults (
4
). Through the CDC Pharmacy Partnership for Long-Term Care Program, SNF residents
and staff members in Connecticut began receiving the Pfizer-BioNTech COVID-19 vaccine
on December 18, 2020 (
5
). Administration of the vaccine was conducted during several on-site pharmacy clinics.
In late January 2021, the Connecticut Department of Public Health (CT DPH) identified
two SNFs experiencing COVID-19 outbreaks among residents and staff members that occurred
after each facility’s first vaccination clinic. CT DPH, in partnership with CDC, performed
electronic chart review in these facilities to obtain information on resident vaccination
status and infection with SARS-CoV-2, the virus that causes COVID-19. Partial vaccination,
defined as the period from >14 days after the first dose through 7 days after the
second dose, had an estimated effectiveness of 63% (95% confidence interval [CI] = 33%–79%)
against SARS-CoV-2 infection (regardless of symptoms) among residents within these
SNFs. This is similar to estimated effectiveness for a single dose of the Pfizer-BioNTech
COVID-19 vaccine in adults across a range of age groups in noncongregate settings
(
6
) and suggests that to optimize vaccine impact among this population, high coverage
with the complete 2-dose series should be recommended for SNF residents and staff
members.
After identification of the first infected SNF resident or staff member through weekly
surveillance testing, expanded facility-wide outbreak SARS-CoV-2 testing was performed
frequently for residents and staff members at both facilities in accordance with CDC
and CT DPH guidelines (
7
). All residents who had not received a positive test result in the preceding 90 days,
regardless of symptoms, received a once-weekly (facility A) or twice-weekly (facility
B) polymerase chain reaction (PCR) test. Staff members were also tested regularly
(once-weekly antigen and once-weekly PCR test at facility A, and once-weekly PCR test
at facility B). At both facilities, supplementary antigen testing was performed immediately
for any resident or staff member who developed COVID-19 symptoms and for residents
who had known COVID-19 exposures.
A retrospective cohort investigation using data from electronic medical record chart
abstraction was conducted to assess vaccine effectiveness. This activity was reviewed
by CDC and was conducted consistent with applicable federal law and CDC policy.
§
The investigation period started on the date of each SNF’s first vaccination clinic
(December 29, 2020 for facility A and December 21, 2020 for facility B) and ended
on February 9, 2021 and February 12, 2021, respectively. Residents were included if
they were admitted at either facility during one or more rounds of facility-wide SARS-CoV-2
testing during the week before or any time after their facility’s first vaccination
clinic. Data on residents were abstracted starting on the date of their SNF’s first
vaccination clinic or their admission into the facility, whichever occurred later.
Electronic medical record data included demographic characteristics, facility admission
and discharge dates, vaccination dates, symptoms of COVID-19 occurring within 7 days
before or 14 days after a positive test result, presence of underlying medical conditions
associated with potential increased risk for severe COVID-19 illness,
¶
and measures of outcome, including hospitalization and death. SARS-CoV-2 test dates,
test types, and results were also obtained from the electronic medical record.
A case was defined as any positive PCR- or antigen-based SARS-CoV-2 test result during
the investigation period in a resident meeting the cohort inclusion criteria. Case
date was defined as either the date of symptom onset or positive SARS-CoV-2 test result,
whichever occurred earlier. Positive SARS-CoV-2 test results received before the investigation
period were identified for each resident using the Connecticut Electronic Disease
Surveillance System.
Person-time began on the date of the facility’s first vaccination clinic or the date
the resident was admitted, whichever occurred later. Residents stopped contributing
person-time to the investigation on the case date, the final facility discharge date
or date of death if applicable, or the final day of the investigation period, whichever
occurred earlier. Resident person-time was categorized as 1) unvaccinated (days from
cohort entry until receipt of first vaccine dose), 2) time before first vaccine dose
effect (day 0 [date of vaccination] through day 14 after first dose), 3) partially
vaccinated (>day 14 after first dose through day 7 after second dose), or 4) fully
vaccinated (>7 days after second dose).
Assuming a common VE against SARS-CoV-2 infection at both facilities, a Cox proportional
hazards model with baseline hazard rates stratified by facility was applied to estimate
the VE, with VE = 100% × (1−hazard ratio); 95% CIs were calculated using robust CI
methods.** Use of a time-to-event analysis was necessary to adjust for expected heterogeneity
in risk for infection across the investigation period attributable to underlying outbreak
dynamics. Kaplan-Meier curves of SARS-CoV-2 infection were constructed to visualize
the cumulative infection-free proportion of residents; 95% CIs were calculated using
Greenwood’s method.
††
Sensitivity analyses were conducted with exclusion of residents with past confirmed
SARS-CoV-2 infection and using two alternative endpoints for partial vaccination (ending
on second dose +0 days and second dose +14 days). The time before first dose vaccine
effect was excluded from the analysis, because immune status could not be clearly
categorized. Small sample sizes precluded separate analyses of VE against symptomatic
or severe disease. R statistical software (version 4.0.2; The R Foundation) was used
to conduct all analyses.
A total of 463 residents were enrolled, including 142 (31%) from facility A and 321
(69%) from facility B. Demographic characteristics such as age and race were similar
in residents at each facility (although ethnicity could not be reported because ethnicity
data were missing for 30% of residents); prevalences of underlying conditions that
increase the risk for severe COVID-19 illness were also similar in residents at each
facility (Table). The median number of high-risk conditions per resident was three;
five (1.1%) residents had no underlying high-risk conditions. Among the 463 residents,
115 (24.8%) had confirmed SARS-CoV-2 infection before the investigation period; two
of 34 (6%) residents at facility A and 68 of 81 (84%) residents at facility B with
past confirmed SARS-CoV-2 infection had a positive test result ≤3 months prior to
investigation start.
TABLE
Demographic characteristics, COVID-19 vaccination status, and SARS-CoV-2 infection,
symptom, and outcome information among residents of two skilled nursing facilities
— Connecticut, December 21, 2020–February 12, 2021
Characteristic
No. (%) of residents*
Total
Facility A
Facility B
p-value†,§
(N = 463)
(n = 142)
(n = 321)
Sex
Female
294 (63.5)
82 (57.8)
212 (66.0)
0.09
Male
169 (36.5)
60 (42.3)
109 (34.0)
Age group, yrs
<60
23 (5.0)
18 (12.7)
5 (1.6)
<0.001
60–64
19 (4.1)
12 (8.5)
7 (2.2)
65–69
34 (7.3)
16 (11.3)
18 (5.6)
70–74
46 (9.9)
14 (9.9)
32 (10.0)
75–79
56 (12.1)
17 (12.0)
39 (12.2)
80–84
54 (11.7)
15 (10.6)
39 (12.2)
≥85
231 (49.9)
50 (35.2)
181 (56.4)
Race¶
American Indian/Alaska Native
1 (0.2)
0 (0.0)
1 (0.3)
0.57§
Asian
5 (1.1)
1 (0.7)
4 (1.3)
Black
16 (3.5)
5 (3.5)
11 (3.4)
Native Hawaiian/Pacific Islander
1 (0.2)
0 (0.0)
1 (0.3)
White
428 (92.4)
135 (95.1)
293 (91.3)
Unknown
12 (2.6)
1 (0.7)
11 (3.4)
High-risk medical conditions**
Obesity
44 (9.5)
16 (11.3)
28 (8.7)
0.39
Chronic kidney disease
92 (19.9)
32 (22.5)
60 (18.7)
0.34
End-stage renal disease requiring dialysis
3 (0.7)
2 (1.4)
1 (0.3)
0.22§
Diabetes mellitus (type I or II)
131 (28.3)
51 (35.9)
80 (24.9)
0.02
Cancer (not in remission)
28 (6.1)
9 (6.3)
19 (5.9)
0.86
Autoimmune disease
33 (7.1)
13 (9.2)
20 (6.2)
0.26
Chronic heart or cardiovascular disease
186 (40.2)
55 (38.7)
131 (40.8)
0.67
Hypertension
352 (76.0)
103 (72.5)
249 (77.6)
0.24
COPD/Sleep apnea/Other chronic respiratory condition
94 (20.3)
34 (23.9)
60 (18.7)
0.20
Immunocompromising conditions††
9 (1.9)
4 (2.8)
5 (1.6)
0.47§
Neurologic/Neurodevelopmental disorders§§
346 (74.7)
105 (73.9)
241 (75.1)
0.80
Other chronic diseases
66 (14.3)
7 (4.9)
59 (18.4)
0.001
None of these conditions
5 (1.1)
1 (0.7)
4 (1.2)
0.10§
History of past COVID-19
Yes
115 (24.8)
34 (23.9)
81 (25.2)
0.76
>3 months before investigation start
45 (9.7)
32 (22.5)
13 (4.0)
<0.001
≤3 months before investigation start
70 (15.1)
2 (1.4)
68 (21.2)
Vaccination coverage among all residents¶¶
None
87 (18.8)
32 (22.5)
55 (17.1)
0.09
1 dose only
72 (15.6)
27 (19.0)
45 (14.0)
2 doses
304 (65.7)
83 (58.5)
221 (68.8)
Interval between vaccine doses
Days between doses 1 and 2, median (range)
21 (21–42)
21 (21–42)
21 (21–32)
N/A
Cases
All cases
97 (21.0)
40 (28.2)
57 (17.8)
0.01
Symptomatic, no. (% of cases)
86 (88.7)
33 (82.5)
53 (93.0)
0.19§
Reported symptoms, no. (% of cases)
None
11 (11.3)
7 (17.5)
4 (7.0)
0.19§
Fever and chills
24 (24.7)
5 (12.5)
19 (33.3)
0.02
Cough
63 (65.0)
21 (52.5)
42 (73.7)
0.03
Shortness of breath/Difficulty breathing
18 (18.6)
8 (20.0)
10 (17.5)
0.76
Myalgias
7 (7.2)
0 (0.0)
7 (12.3)
0.04§
Headaches
3 (3.1)
2 (5.0)
1 (1.8)
0.57§
Sore throat
5 (5.2)
0 (0.0)
5 (8.8)
0.08§
New loss of taste or smell
1 (1.0)
0 (0.0)
1 (1.8)
N/A
Congestion/Rhinorrhea
16 (16.5)
6 (15.0)
10 (17.5)
0.74
Abdominal pain
3 (3.1)
2 (5.0)
1 (1.8)
0.57§
Nausea/Vomiting
12 (12.4)
2 (5.0)
10 (17.5)
0.11§
Diarrhea
6 (6.2)
1 (2.5)
5 (8.8)
0.40§
Confusion/Altered mental status
21 (21.7)
11 (27.5)
10 (17.5)
0.24
Other***
65 (67.0)
26 (65.0)
39 (68.4)
0.72
Vaccination status on case date, no. (% of cases)
Unvaccinated
39 (40.2)
15 (37.5)
24 (42.1)
0.16§
Before dose 1 effect (day 0 through day 14 after dose 1)
26 (26.8)
15 (37.5)
11 (19.3)
Partially vaccinated (>day 14 after dose 1 through day 7 after dose 2)
25 (25.8)
9 (22.5)
16 (28.1)
Fully vaccinated (>7 days after dose 2)
7 (7.2)
1 (2.5)
6 (10.5)
Outcomes,††† no. (% of cases)
Hospitalization
15 (15.5)
4 (10.0)
11 (19.3)
0.21
Vital status dead or unknown
Death from COVID-19
17 (17.5)
7 (17.5)
10 (17.5)
0.55§
Death after diagnosis (no cause specified)
4 (4.1)
1 (2.5)
3 (5.3)
Vital status unknown
3 (3.1)
0 (0.0)
3 (5.3)
Abbreviations: COPD = chronic obstructive pulmonary disease; N/A = not applicable.
* Percentages might not sum to 100% because of rounding.
† P-values for the comparisons between facilities apply Pearson’s chi-square test
for independence unless marked. For mutually exclusive categories of a characteristic
a single p-value is reported. For characteristics for which more than one category
might be true for a resident (e.g., symptoms), individual p-values are reported for
each category.
§ In cases with cell counts <5, Fisher’s exact test was used to calculate the p-value.
¶ Ethnicity is not reported because data were missing for 30% of residents.
** Conditions associated with potential increased risk for severe COVID-19 illness
per CDC guidelines.
†† HIV coinfection (not virally suppressed), chemotherapy within past 12 months, solid-organ
or bone marrow transplant, long-term steroid use (20 mg per day for >1 month), taking
immunosuppressants, or taking tumor necrosis factor-alpha inhibitors.
§§ Examples include seizure disorders such as epilepsy, Alzheimer disease, dementia,
traumatic brain injuries, and stroke.
¶¶ Vaccination is reported as the percentage of all residents included in the investigation
that received no dose, 1 dose, or 2 doses of Pfizer-BioNTech COVID-19 vaccine by the
date of their discharge from the facility or the end of the investigation if they
were still admitted to the facility. Absolute coverage in the facility changed daily
because of changes in census.
*** Other symptoms included lethargy, fatigue, generalized weakness, malaise, decreased
appetite or loss of appetite, and agitation.
††† Case outcomes include minimum number of confirmed COVID-19–related hospitalizations
and COVID-19 deaths confirmed by the Office of the Chief Medical Examiner. Hospitalizations
and deaths that occurred after the investigation period were not ascertained.
During the investigation period, 97 cases of SARS-CoV-2 infection occurred, including
40 (41%) at facility A and 57 (59%) at facility B (Figure 1). Including nonspecific
symptoms such as malaise, lethargy, and decreased appetite, at least one COVID-19
symptom was reported in 86 (88.7%) cases.
§§
By the date of discharge or the last day of the investigation, 304 residents (65.7%)
had received 2 vaccine doses, 72 (15.6%) had received 1 dose only, and 87 (18.8%)
had not received any doses. A total of 16,969 person-days were observed during the
investigation period, with 39 cases occurring during 3,573 days categorized as unvaccinated
person-time, 26 cases during 4,588 days of person-time before first vaccine dose effect,
25 cases during 4,147 days of partially vaccinated person-time, and seven cases during
4,661 days of fully vaccinated person-time.
FIGURE 1
New SARS-CoV-2 cases* among residents of two skilled nursing facilities, by case date
†
— Connecticut, December 21, 2020–February 12, 2021§
* Any positive SARS-CoV-2 polymerase chain reaction or antigen test result.
† Symptom onset date or positive test result date, whichever occurred earlier.
§ Investigation period was December 29, 2020–February 9, 2021 for facility A and December
21, 2020–February 12, 2021 for facility B.
The figure is a histogram, an epidemiologic curve showing new SARS-CoV-2 cases among
residents of two skilled nursing facilities, by case date, in Connecticut, during
December 21, 2020–February 12, 2021.
Estimated effectiveness of partial vaccination in preventing SARS-CoV-2 infection
was 63% (95% CI = 33%–79%) and was similar when residents with past SARS-CoV-2 were
excluded (VE = 60%, 95% CI = 30%–77%). VE estimates were also similar in both partial
vaccination endpoint sensitivity analyses (second dose +0 days VE = 66%, 95% CI = 29%–83%;
second dose +14 days VE = 60%, 95% CI = 33%–77%). As a result of the course of the
outbreaks at both facilities, most cases occurred toward the start of the investigation
period (Figure 2), and because the cohort began at the first vaccination clinic, most
of the unvaccinated person-time also occurred toward the start of the investigation
period. Thus, once residents became fully vaccinated (second dose +7 days) toward
the end of the investigation period, there were insufficient new cases and remaining
person-time in the unvaccinated group to serve as a comparator for estimation of full
2-dose VE.
FIGURE 2
Proportion of skilled nursing facility residents who remained uninfected with SARS-CoV-2
during the investigation period,* by COVID-19 vaccination status
†
and facility — Connecticut, December 21, 2020–February 12, 2021
* Investigation period was December 29, 2020–February 9, 2021 for facility A and December
21, 2020–February 12, 2021 for facility B.
† Vaccination status is classified as unvaccinated or partially vaccinated. Partially
vaccinated refers to the time from day 14 after first dose of Pfizer-BioNTech COVID-19
vaccine through day 7 after the second dose. Greenwood’s method was used to estimate
confidence intervals around the Kaplan-Meier estimator.
The figure is a line chart showing the proportion of skilled nursing facility residents
who remained uninfected with SARS-CoV-2 during the investigation period, by COVID-19
vaccination status and facility, in Connecticut, during December 21, 2020–February
12, 2021.
Discussion
Partial vaccination with the Pfizer-BioNTech COVID-19 vaccine was 63% effective in
preventing new SARS-CoV-2 infections in SNF residents, a disproportionately affected
population excluded from initial preauthorization vaccine clinical trials. Even during
a large disease outbreak in a long-term care setting, the Pfizer-BioNTech vaccine
provided protection against SARS-CoV-2 infection, including in older adults aged ≥65
years with a high prevalence of underlying medical conditions. The findings in this
report are comparable to other first-dose vaccine efficacy and effectiveness estimates
for the Pfizer-BioNTech vaccine for the broader adult population in noncongregate
settings. In the phase 3 clinical trial, efficacy during the interval between first
and second doses was estimated at 52% (95% CI = 30%–68%) (
8
). In a recent study of the Pfizer-BioNTech vaccine in Israel, effectiveness against
PCR-confirmed infection in the general adult population during days 14–20 and 21–27
after the first dose was 46% (95% CI = 40%–51%) and 60% (95% CI = 53%–66%, respectively)
(
6
). Effectiveness was somewhat lower during days 14–20 and 21–27 among persons aged
≥70 years (22%; 95% CI = −9%–44% and 50%; 95% CI = 19%–72%, respectively) and among
those with three or more underlying medical conditions (37%; 95% CI = 12%–55% and
37%; 95% CI = −1%–62%) (
6
).
In this investigation, nearly 25% of residents had confirmed past SARS-CoV-2 infection.
Serologic studies have indicated that preexisting immunity might strengthen the response
to a single dose of COVID-19 vaccine (
9
). A sensitivity analysis excluding person-time contributed by residents with confirmed
past infections did not substantially alter VE estimates for residents receiving the
first vaccine dose. Among residents in this investigation with past confirmed SARS-CoV-2
infection, first-dose vaccination rates were >90%, and only one reinfection was documented,
limiting the ability to determine the impact of past infection.
The findings in this report are subject to at least seven limitations. First, because
there were no clear factors that would differentially affect the risk for infection
among residents within either facility, such as units with higher attack rates or
different infection prevention practices, each observation in the model was treated
as independent. If risk was not independent, this could have biased the VE estimates.
Second, 2-dose VE estimates were not possible because unvaccinated cases and person-time
after second-dose vaccination clinics were insufficient. Third, small sample sizes
did not allow for analyses of secondary endpoints, such as effectiveness against symptomatic
illness, hospitalization, or death. Fourth, although there was no change in guidance
around outbreak control measures such as cohorting and other infection prevention
and control strategies concurrent with vaccine introduction, had these measures been
implemented differently for vaccinated and unvaccinated residents, VE estimates could
have been biased. Fifth, racial minority groups were underrepresented in this investigation
compared with the general population of older adults, and ethnicity data were missing
for approximately one third of residents, which might affect generalizability to other
SNF populations. Sixth, although excluding person-time from residents with known past
confirmed SARS-CoV-2 infection did not influence VE estimates in this analysis, there
could have been residents with unknown past infection who could still have acted as
a source of potential bias. Finally, unrecognized underlying differences between vaccinated
and unvaccinated residents might have confounded the effectiveness estimates. Strengths
of the investigation include accurate collection of vaccination data through direct
abstraction from resident electronic medical records and active ascertainment of SARS-CoV-2
infection through frequent, facility-wide resident testing.
Findings from this retrospective cohort analysis demonstrate that partial vaccination
with the Pfizer-BioNTech COVID-19 vaccine was associated with a significant reduction
in the risk for SARS-CoV-2 infection among SNF residents. These results, coupled with
the findings from a previous study among comparable older adult populations in Israel
that reported more robust protection after the second dose (
6
), suggest that complete 2-dose vaccination is an important strategy for preventing
COVID-19 in this disproportionately affected population. Further study of this population
should continue as larger sample sizes become available. LTCFs and jurisdictions should
actively ensure that they have plans in place for continued allocation and administration
of COVID-19 vaccines to residents and staff members (
10
).
Summary
What is already known about this topic?
Skilled nursing facility (SNF) residents, generally older and with more underlying
medical conditions than community-dwelling adults, were not included in COVID-19 vaccine
clinical trials. Little is known about COVID-19 vaccine effectiveness in SNF residents.
What is added by this report?
A retrospective cohort analysis in two Connecticut SNFs found partial vaccination
with Pfizer-BioNTech COVID-19 vaccine (from >14 days after dose 1 through 7 days after
dose 2) to be 63% (95% confidence interval = 33%–79%) effective against SARS-CoV-2
infection.
What are the implications for public health practice?
Even with partial vaccination, Pfizer-BioNTech COVID-19 vaccine provides protection
to SNF residents. To optimize vaccine impact among this population, high coverage
with the complete 2-dose series is recommended.