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. 2021 Jul 7:NEJMoa2107715. doi: 10.1056/NEJMoa2107715

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.

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