Table 2. Effectiveness of CoronaVac Vaccine in Preventing Covid-19 Outcomes in Overall Study Cohort, According to Immunization Status.*.
| Outcome and Immunization Status | Study Cohort | Persons with Covid-19 | Vaccine Effectiveness (95% CI) | |||
|---|---|---|---|---|---|---|
| No. of Person-Days |
No. of Persons |
Incidence Rate |
Analysis Adjusted for Sex and Age |
Analysis Adjusted for All Covariates† |
Stratified Analysis‡ |
|
| no. of events/ 1000 person-days |
percent | |||||
| Covid-19 | ||||||
| Unvaccinated | 614,868,240 | 185,633 | 0.3019 | — | — | — |
| Partially immunized | 69,788,352 | 20,865 | 0.2990 | 8.0 (6.5–9.4) |
15.5 (14.2–16.8) |
17.2 (15.8–18.6) |
| Fully immunized | 91,671,797 | 12,286 | 0.1340 | 61.2 (60.3–62.0) |
65.9 (65.2–66.6) |
63.7 (62.8–64.6) |
| Hospitalization | ||||||
| Unvaccinated | 620,894,706 | 18,034 | 0.0290 | — | — | — |
| Partially immunized | 70,690,796 | 3,370 | 0.0477 | 31.4 (28.6–34.0) |
37.4 (34.9–39.9) |
40.3 (37.6–42.8) |
| Fully immunized | 92,445,333 | 1,462 | 0.0158 | 86.0 (85.1–86.8) |
87.5 (86.7–88.2) |
86.5 (85.6–87.4) |
| Admission to ICU | ||||||
| Unvaccinated | 621,226,431 | 6,359 | 0.0102 | — | — | — |
| Partially immunized | 70,836,597 | 1,154 | 0.0163 | 37.5 (33.1–41.5) |
44.7 (40.8–48.3) |
45.3 (41.2–49.2) |
| Fully immunized | 92,622,083 | 360 | 0.0039 | 88.8 (87.4–90.0) |
90.3 (89.1–91.4) |
90.2 (88.9–91.4) |
| Confirmed death | ||||||
| Unvaccinated | 621,426,477 | 2,786 | 0.0045 | — | — | — |
| Partially immunized | 70,854,187 | 847 | 0.0120 | 39.8 (34.4–44.7) |
45.7 (40.9–50.2) |
46.0 (40.7–50.8) |
| Fully immunized | 92,514,261 | 409 | 0.0044 | 84.4 (82.4–86.2) |
86.3 (84.5–87.8) |
86.7 (84.9–88.3) |
Participants were classified into three groups: those who were unvaccinated, those who were partially immunized (≥14 days after receipt of the first vaccine dose and before receipt of the second dose), and those who were fully immunized (≥14 days after receipt of the second dose). The 13 days between vaccine administration and partial or full immunization were excluded from the at-risk person-time. ICU denotes intensive care unit.
The analysis was adjusted for age, sex, region of residence, income, nationality, and whether the patient had underlying conditions that have been associated with severe Covid-19.
A stratified version of the extended Cox proportional-hazards model was fit to test the robustness of the estimates to model assumptions, with stratification according to age, sex, region of residence, income, nationality, and whether the patient had underlying conditions that have been associated with severe Covid-19.