Table 2. Incident COVID-19 Cases and Vaccine Efficacy 14 Days After 2 Doses of Immunization^a.

Outcome	WIV04 vaccine group	HB02 vaccine group	Alum-only group
Primary analysis: incident symptomatic cases
No. of participants	12 743	12 726	12 737
No. of incident cases	26	21	95
Person-years	2140.2	2143.3	2125.6
Incidence density per 1000 person-years (95% CI)	12.1 (8.3-17.8)	9.8 (6.4-15.0)	44.7 (36.6-54.6)
Vaccine efficacy (95% CI), %	72.8 (58.1-82.4)	78.1 (64.8-86.3)	[Reference]
Secondary analysis: incident severe cases
No. of participants	12 743	12 726	12 737
No. of incident cases	0	0	2
Person-years	2140.2	2143.3	2125.6
Incidence density per 1000 person-years (95% CI)	0 (NA)	0 (NA)	9 (1.0-34.0)
Vaccine efficacy (95% CI), %	100 (NA)	100 (NA)	[Reference]
Post hoc analysis: incident symptomatic and asymptomatic casesb
No. of participants	12 727	12 713	12 722
No. of incident cases	42	31	116
Person-years	2135.5	2139.6	2121.0
Incidence density per 1000 person-years (95% CI)	19.7 (14.5-26.6)	14.5 (10.2-20.6)	54.7 (45.6-65.6)
Vaccine efficacy (95% CI), %	64.0 (48.8-74.7)	73.5 (60.6-82.2)	[Reference]

Abbreviations: alum, aluminum hydroxide; NA, not applicable.

^aThe analyses were conducted in the modified full analysis population-1, which included those who received 2 doses, contributed at least 1 efficacy follow-up visit, and had negative polymerase chain reaction test results at enrollment. A Poisson regression model with log-link function was used, with the number of incident cases as the dependent variable, treatment group as the independent variable, and person-years as the offset. Incidence density with its 95% CI was estimated using the least-square method. If the number of cases in any of the groups was less than 5, the exact method was used to estimate the incidence rate, vaccine efficacy, and 95% CI using StatXact software.

^bForty-four participants were excluded from the analysis because they had asymptomatic COVID-19 between the first dose and 14 days after the second dose.