Table 4. Estimated Effectiveness of mRNA Vaccines among Health Care Personnel in Subgroups Defined According to Risk Factors, Age Group, and Race and Ethnic Group.*.
| Variable | Case Participants (N=1472) |
Control Participants (N=3420) |
Vaccine Effectiveness (95% CI) | |
|---|---|---|---|---|
| Unadjusted Analysis | Adjusted Analysis† | |||
| no./total no. (%) | percent | |||
| Risk factors | ||||
| Underlying condition or risk factor that increases risk of severe Covid-19‡ | ||||
| ≥1 Underlying condition or risk factor | ||||
| Partial vaccination | 110/1126 (10) | 627/2561 (24) | 79.3 (73.2 to 84.0) | 76.4 (69.0 to 82.0) |
| Complete vaccination | 118/1126 (10) | 784/2561 (31) | 90.1 (85.8 to 92.7) | 90.3 (86.4 to 93.0) |
| ≥2 Underlying conditions or risk factors | ||||
| Partial vaccination | 69/697 (10) | 409/1639 (25) | 81.1 (72.7 to 85.5) | 76.7 (67.4 to 83.3) |
| Complete vaccination | 80/697 (11) | 500/1639 (31) | 88.8 (84.0 to 92.2) | 88.5 (83.2 to 92.2) |
| ≥3 Underlying conditions or risk factors | ||||
| Partial vaccination | 43/407 (11) | 235/944 (25) | 79.6 (69.5 to 86.4) | 76.1 (63.4 to 84.3) |
| Complete vaccination | 50/407 (12) | 298/944 (32) | 89.5 (83.7 to 93.3) | 89.4 (83.1 to 93.4) |
| No underlying condition or risk factor | ||||
| Partial vaccination | 30/346 (9) | 236/859 (27) | 87.0 (79.4 to 91.8) | 87.5 (79.7 to 92.3) |
| Complete vaccination | 49/346 (14) | 288/859 (34) | 91.0 (85.8 to 94.3) | 91.1 (85.5 to 94.6) |
| Any immunocompromising condition, assessed for partial and complete vaccination§¶ | 23/64 (36) | 58/124 (47) | 52.4 (−6.4 to 78.7) | 39.1 (−45.0 to 74.4) |
| Obesity‖ | ||||
| Partial vaccination | 47/529 (9) | 254/1068 (24) | 81.6 (72.9 to 87.5) | 80.2 (70.3 to 86.8) |
| Complete vaccination | 49/529 (9) | 321/1068 (30) | 91.2 (86.6 to 94.2) | 92.1 (87.6 to 95.0) |
| Obesity or overweight‖ | ||||
| Partial vaccination | 97/954 (10) | 490/2022 (24) | 78.2 (71.2 to 83.5) | 76.5 (68.4 to 82.5) |
| Complete vaccination | 93/954 (10) | 633/2022 (31) | 90.7 (87.0 to 93.4) | 91.0 (87.0 to 93.7) |
| Hypertension | ||||
| Partial vaccination | 17/215 (8) | 120/485 (25) | 85.8 (74.1 to 92.2) | 83.1 (68.1 to 91.0) |
| Complete vaccination | 22/215 (10) | 148/485 (31) | 91.3 (83.7 to 95.3) | 91.8 (83.9 to 95.8) |
| Asthma | ||||
| Partial vaccination | 20/207 (10) | 155/616 (25) | 81.8 (67.6 to 89.7) | 77.8 (59.5 to 87.8) |
| Complete vaccination | 21/207 (10) | 175/616 (28) | 90.7 (82.8 to 94.9) | 90.5 (81.9 to 95.0) |
| Diabetes | ||||
| Partial vaccination | 4/69 (6) | 42/159 (26) | 89.0 (64.9 to 96.5) | 85.5 (52.3 to 95.6) |
| Complete vaccination | 10/69 (14) | 42/159 (26) | 79.2 (48.2 to 91.7) | 80.2 (45.8 to 92.7) |
| Pregnancy, assessed for partial and complete vaccination¶ | 6/62 (10) | 28/91 (31) | 83.8 (54.5 to 94.2) | 77.1 (32.2 to 92.2) |
| Age | ||||
| <50 yr | ||||
| Partial vaccination | 106/1128 (9) | 644/2568 (25) | 81.5 (76.1 to 85.7) | 80.3 (74.2 to 85.0) |
| Complete vaccination | 130/1128 (12) | 810/2568 (32) | 90.2 (86.6 to 92.7) | 90.3 (86.5 to 93.0) |
| ≥50 yr | ||||
| Partial vaccination | 34/331 (10) | 205/816 (25) | 78.6 (66.1 to 86.5) | 77.0 (62.7 to 85.8) |
| Complete vaccination | 36/331 (11) | 256/816 (31) | 89.0 (82.0 to 93.3) | 90.7 (84.2 to 94.6) |
| Race and ethnic group | ||||
| White, non-Hispanic | ||||
| Partial vaccination | 103/973 (11) | 641/2478 (26) | 79.7 (73.4 to 84.5) | 79.3 (72.5 to 84.4) |
| Complete vaccination | 127/973 (13) | 815/2478 (33) | 89.5 (85.5 to 92.3) | 90.1 (86.2 to 93.0) |
| Black, non-Hispanic | ||||
| Partial vaccination | 7/188 (4) | 40/259 (15) | 85.3 (64.9 to 93.9) | 85.7 (64.7 to 94.2) |
| Complete vaccination | 6/188 (3) | 44/259 (17) | 94.4 (82.7 to 98.2) | 94.8 (83.3 to 98.4) |
| Hispanic or Latino | ||||
| Partial vaccination | 12/157 (8) | 69/281 (25) | 81.3 (61.1 to 91.0) | 81.6 (60.5 to 91.5) |
| Complete vaccination | 16/157 (10) | 74/281 (26) | 86.4 (73.1 to 93.1) | 89.4 (78.0 to 94.9) |
| Asian or Pacific Islander, non-Hispanic | ||||
| Partial vaccination | 9/84 (11) | 74/268 (28) | 80.5 (54.3 to 91.7) | 79.6 (50.4 to 91.6) |
| Complete vaccination | 11/84 (13) | 99/268 (37) | 90.3 (77.4 to 95.9) | 89.3 (74.2 to 95.6) |
| American Indian or Alaska Native, non-Hispanic | ||||
| Partial vaccination | 5/34 (15) | 13/47 (28) | 78.3 (5.8 to 95.0) | 75.9 (−7.7 to 94.6) |
| Complete vaccination | 6/34 (18) | 1/47 (2) | 91.0 (57.3 to 98.1) | 93.7 (69.4 to 98.7) |
Vaccine effectiveness was calculated as 1 minus the matched odds ratio (×100%) for partial or complete vaccination, as compared with no vaccination, and was estimated with the use of a conditional logistic-regression model with accounting for matching according to site of enrollment and week of test date. The reference group in the analysis of effectiveness in all categories was the group of unvaccinated participants. For partial vaccination, the effectiveness of a single dose was assessed during the interval from 14 days after receipt of the first dose through 6 days after receipt of the second dose. For complete vaccination, the effectiveness of two doses was assessed at least 7 days after the receipt of the second dose (consistent with the Pfizer–BioNTech clinical trial7).
The odds ratio was adjusted for age, race and ethnic group, presence of underlying conditions, and close contact with patients with Covid-19 in the workplace or persons with Covid-19 outside the workplace.
We defined conditions as being associated with a definite or potential increased risk of severe Covid-19 according to the definitions of the Centers for Disease Control and Prevention (https://www.cdc.gov/coronavirus/2019-ncov/need-extra-precautions/people-with-medical-conditions.html).
Immunocompromising conditions included receipt of immunosuppressive medication (e.g., glucocorticoids, chemotherapy, or other immunosuppressive medication), solid-organ transplantation, hematopoietic stem-cell transplantation, human immunodeficiency virus infection, or active cancer (current cancer or treatment for cancer or receipt of diagnosis in the preceding 12 months).
The sample size was limited for the evaluation of effectiveness according to vaccination status. Therefore, vaccine effectiveness was assessed in the interval from at least 14 days after receipt of the first dose through the receipt of the second dose or later.
Obesity was defined as a body-mass index (BMI; the weight in kilograms divided by the square of the height in meters) of 30 or higher, and overweight as a BMI of 25 to 29.