Effectiveness of BNT162b2 and CoronaVac vaccines in preventing SARS-CoV-2 Omicron infections, hospitalizations, and severe complications in the pediatric population in Hong Kong: a case-control study

Figures & data

Figure 1. Selection of cases and controls.

Table 1. Baseline characteristics of cases and controls.

Outcomes	Infection		Hospitalization		Severe COVID-19
	Cases	Controls	Cases	Controls	Cases	Controls
Number of individuals	36,434	109,004	2231	21,788	1918	18,823
Age, years (mean (SD))	10.35 (4.00)	10.35 (4.00)	8.70 (4.38)	8.67 (4.38)	8.53 (4.31)	8.50 (4.30)
Sex, male (%)	20766 (57.0)	62211 (57.1)	1283 (57.5)	12561 (57.7)	1106 (57.7)	10871 (57.8)
Charlson Comorbidity Index (mean (SD))	0.03 (0.19)	0.03 (0.18)	0.07 (0.34)	0.03 (0.20)	0.05 (0.30)	0.03 (0.19)
Time since recent dose (mean (SD))	88.72 (80.59)	75.75 (80.79)	85.07 (67.14)	81.05 (72.60)	84.41 (66.22)	79.38 (69.90)
Comorbidities – no. (%)
Asthma	789 (2.2)	1955 (1.8)	53 (2.4)	467 (2.1)	40 (2.1)	333 (1.8)
Diabetes	45 (0.1)	251 (0.2)	9 (0.4)	46 (0.2)	7 (0.4)	32 (0.2)
Epilepsy	237 (0.7)	1961 (1.8)	83 (3.7)	200 (0.9)	77 (4.0)	180 (1.0)
Medication use within 90 days – no. (%)
Immunosuppressants	36 (0.1)	223 (0.2)	13 (0.6)	43 (0.2)	9 (0.5)	37 (0.2)

Figure 2. Vaccine effectiveness among children and adolescents with different vaccination status.

Table 2. Vaccine effectiveness among children and adolescents with different vaccination status.

Vaccination status	Case	Control	Crude OR (95% CI)	Adjusted OR (95% CI)	VE% (95% CI)
COVID-19
Unvaccinated	17,825	48,738	(Ref)	(Ref)	(Ref)
1 dose
BNT162b2	4100	13,241	0.733 (0.700–0.769)	0.721 (0.688–0.756)	27.9 (24.4; 31.2)
CoronaVac	6011	20,016	0.800 (0.772–0.828)	0.793 (0.766–0.821)	20.7 (17.9; 23.4)
2 doses
All BNT162b2	5401	17,121	0.704 (0.670–0.741)	0.687 (0.653–0.722)	31.3 (27.8; 34.7)
All CoronaVac	2522	7595	0.793 (0.748–0.842)	0.783 (0.738–0.830)	21.7 (17.0; 26.2)
3 doses
All BNT162b2	389	1660	0.449 (0.392–0.514)	0.440 (0.384–0.504)	56.0 (49.6; 61.6)
All CoronaVac	130	463	0.619 (0.505–0.759)	0.606 (0.494–0.744)	39.4 (25.6; 50.6)
B-B-C	55	161	0.674 (0.492–0.922)	0.656 (0.480–0.899)	34.4 (10.1; 52.0)
C-C-B	1	9	0.229 (0.029–1.814)	0.225 (0.028–1.783)	77.5 (−78.3; 97.2)
COVID-19-related hospitalization
Unvaccinated	1188	11,181	(Ref)	(Ref)	(Ref)
1 dose
BNT162b2	157	1631	0.758 (0.619–0.928)	0.796 (0.650–0.975)	20.4 (2.5; 35.0)
CoronaVac	290	2993	0.902 (0.781–1.042)	0.919 (0.795–1.062)	8.1 (−6.2; 20.5)
2 doses
All BNT162b2	202	2494	0.588 (0.480–0.720)	0.624 (0.509–0.766)	37.6 (23.4; 49.1)
All CoronaVac	343	2753	1.147 (0.975–1.348)	1.175 (0.998–1.383)	−17.5 (−38.3; 0.2)
3 doses
All BNT162b2	29	478	0.385 (0.248–0.599)	0.411 (0.264–0.639)	58.9 (36.1; 73.6)
All CoronaVac	12	213	0.477 (0.261–0.872)	0.483 (0.264–0.884)	51.7 (11.6; 73.6)
B-B-C	10	43	1.511 (0.727–3.140)	1.563 (0.751–3.250)	−56.3 (−225.0; 24.9)
C-C-B	0	2	–	–	–
Severe COVID-19
Unvaccinated	1044	9956	(Ref)	(Ref)	(Ref)
1 dose
BNT162b2	128	1307	0.780 (0.623–0.976)	0.809 (0.646–1.013)	19.1 (−1.3; 35.4)
CoronaVac	247	2596	0.897 (0.767–1.049)	0.912 (0.779–1.068)	8.8 (−6.8; 22.1)
2 doses
All BNT162b2	165	2079	0.586 (0.469–0.732)	0.609 (0.488–0.762)	39.1 (23.8; 51.2)
All CoronaVac	294	2306	1.231 (1.029–1.474)	1.249 (1.042–1.497)	−24.9 (−49.7; −4.2)
3 doses
All BNT162b2	22	360	0.379 (0.228–0.631)	0.398 (0.239–0.663)	60.2 (33.7; 76.1)
All CoronaVac	12	182	0.584 (0.318–1.072)	0.578 (0.314–1.062)	42.2 (−6.2; 68.6)
B-B-C	6	35	1.107 (0.444–2.764)	1.120 (0.448–2.799)	−12.0 (−179.9; 55.2)
C-C-B	0	2	–	–	–

OR: odds ratio, VE: vaccine effectiveness, CI: confidence interval, B-B-C: two doses of BNT162b2 followed by CoronaVac, C-C-B: two doses of CoronaVac followed by BNT162b2.

Figure 3. Vaccine effectiveness for different time-since-vaccination intervals after second dose.

Table 3. Vaccine effectiveness for different time-since-vaccination intervals.

Days since vaccine dose	VE % (95% CI)
	0–13	14–60	61–120	121–180	≥180
COVID-19
Unvaccinated	(Ref)	(Ref)	(Ref)	(Ref)	(Ref)
1 dose
BNT162b2	57.9 (53.7–61.8)	28.9 (21.3–35.8)	−6.0 (−26.1–10.8)	−34.1 (−50.4 to −19.5)	−5.6 (−21.7–8.4)
CoronaVac	35.1 (32.0–38.0)	−6.3 (−12.5 to −0.5)	29.3 (−1.7–50.8)	26.9 (−6.2–49.6)	–
2 doses
All BNT162b2	58.7 (47.8–67.3)	39.7 (29.0–48.7)	20.0 (3.2–33.9)	−7.4 (−20.7–4.4)	16.5 (8.7–23.6)
All CoronaVac	43.0 (35.2–49.8)	29.5 (20.1–37.7)	−10.3 (−26.5–3.8)	−35.2 (−63.3 to −12.0)	–
3 doses
All BNT162b2	78.3 (63.4–87.1)	39.1 (13.1–57.3)	24.8 (−2.3–44.7)	15.6 (−26.8–43.8)	–
All CoronaVac	38.6 (−26.9–70.3)	−1.4 (−57.6–34.8)	33.9 (−49.4–70.8)	76.7 (−97.5–97.3)	–
B-B-C	49.3 (−53.3–83.2)	54.8 (−21.7–83.2)	−13.6 (−118.7–41.0)	11.0 (−158.8–69.4)	–
C-C-B	–	–	–	–	–
COVID-19-related hospitalization
Unvaccinated	(Ref)	(Ref)	(Ref)	(Ref)	(Ref)
1 dose
BNT162b2	19.2 (−25.2–47.8)	45.7 (18.2–64.0)	0.0 (−64.1–39.1)	−0.4 (−42.7–29.4)	26.8 (−52.6–64.9)
CoronaVac	7.5 (−13.7–24.7)	−3.4 (−27.3–15.9)	55.1 (9.7–77.6)	70.6 (34.7 to −86.8)	–
2 doses
All BNT162b2	81.0 (35.2–94.4)	45.5 (−0.2–70.3)	27.1 (−14.9–53.7)	30.4 (0.4–51.3)	33.6 (5.5–53.3)
All CoronaVac	22.0 (−20.0–49.3)	55.8 (34.9–70.0)	−39.0 (−77.4 to −8.9)	−66.9 (−137.3 to −17.3)	–
3 doses
All BNT162b2	91.9 (36.4–99.0)	58.9 (−15.4–85.4)	46.7 (−11.0–74.4)	62.0 (−43.3–89.9)	–
All CoronaVac	22.4 (−190.8–79.3)	69.5 (12.8–89.3)	−91.0 (−745.5–56.8)	–	–
B-B-C	–	–	–	–	–
C-C-B	–	–	–	–	–
Severe COVID-19
Unvaccinated	(Ref)	(Ref)	(Ref)	(Ref)	(Ref)
1 dose
BNT162b2	10.9 (−40.6–43.6)	47.8 (15.0–68.0)	23.2 (−32.7–55.6)	−6.9 (−55.4–26.5)	20.2 (−80.3–64.7)
CoronaVac	3.0 (−20.2–21.7)	−6.5 (−35.6–16.3)	39.8 (−22.7–70.5)	65.7 (22.0–84.9)	–
2 doses
All BNT162b2	70.5 (−9.4–92.1)	67.3 (34.1–83.8)	48.0 (13.4–68.8)	21.4 (−13.6–45.7)	29.2 (−4.9–52.2)
All CoronaVac	6.5 (−53.4–43.0)	57.6 (32.8–73.2)	−42.5 (−84.6 to −10.1)	−48.8 (−120.0 to −0.7)	–
3 doses
All BNT162b2	–	73.3 (20.5–91.0)	75.9 (43.6–89.7)	76.2 (−37.9–95.9)	–
All CoronaVac	58.8 (−58.5–89.3)	75.7 (23.7–92.3)	−33.8 (−463.6–68.2)	–	–
B-B-C	–	–	–	–	–
C-C-B	–	–	–	–	–

OR: odds ratio, VE: vaccine effectiveness, CI: confidence interval, B-B-C: two doses of BNT162b2 followed by CoronaVac, C-C-B: two doses of CoronaVac followed by BNT162b2.

Table 4. Subgroup analyses by age.

Vaccination status	Aged 3–11			Aged 12–17
	Case	Control	VE % (95% CI)	Case	Control	VE% (95% CI)
COVID-19
Unvaccinated	14,560	40,045	(Ref)	3265	8693	(Ref)
1 dose
BNT162b2	579	3256	55.0 (50.6; 59.0)	3521	9985	11.9 (6.3; 17.1)
CoronaVac	4766	16,069	22.3 (19.1; 25.3)	1245	3947	17.7 (11.1; 23.8)
2 doses
All BNT162b2	174	742	45.3 (34.1; 54.5)	5227	16,379	23.1 (18.4; 27.5)
All CoronaVac	1571	4587	17.5 (10.5; 24.0)	951	3008	23.5 (16.3; 30.1)
3 doses
All BNT162b2	0	0	–	389	1660	52.0 (44.8; 58.2)
All CoronaVac	67	259	39.1 (19.3; 54.1)	63	204	35.6 (13.2; 52.2)
B-B-C	0	0	–	55	161	28.0 (1.3; 47.5)
C-C-B	1	2	−16.0 (−1184.2; 89.5)	0	7	–
COVID-19-related hospitalization
Unvaccinated	1009	9817	(Ref)	179	1364	(Ref)
1 dose
BNT162b2	36	460	23.3 (−10.1; 46.5)	121	1171	23.1 (0.2; 40.8)
CoronaVac	249	2612	6.3 (−9.7; 20.0)	41	381	19.4 (−16.9; 44.4)
2 doses
All BNT162b2	15	273	44.7 (3.4; 68.4)	187	2221	40.3 (23.6; 53.3)
All CoronaVac	270	2225	−23.9 (−49.8; −2.5)	73	528	3.8 (−34.0; 31.0)
3 doses
All BNT162b2	0	0	–	29	478	61.9 (39.3; 76.0)
All CoronaVac	7	141	51.9 (−5.3; 78.0)	5	72	54.0 (−19.5; 82.3)
B-B-C	0	0	–	10	43	−45.9 (−207.1; 30.7)
C-C-B	0	0	–	0	2	–
Severe COVID-19
Unvaccinated	899	8826	(Ref)	145	1130	(Ref)
1 dose
BNT162b2	32	378	17.1 (−22.0; 43.7)	96	929	20.3 (−6.8; 40.6)
CoronaVac	217	2279	6.0 (−11.4; 20.7)	30	317	27.8 (−11.2; 53.2)
2 doses
All BNT162b2	14	276	48.4 (8.1; 71.0)	151	1803	39.5 (20.6; 53.9)
All CoronaVac	235	1936	−24.4 (−53.1; −1.1)	59	370	−20.0 (−75.7; 18.1)
3 doses
All BNT162b2	0	0	–	22	360	60.7 (32.6; 77.0)
All CoronaVac	7	127	47.6 (−15.3; 76.2)	5	55	35.5 (−70.8; 75.6)
B-B-C	0	0	–	6	35	−8.7 (−177.6; 57.5)
C-C-B	0	0	–	0	2	–

OR: odds ratio, VE: vaccine effectiveness, CI: confidence interval, B-B-C: two doses of BNT162b2 followed by CoronaVac, C-C-B: two doses of CoronaVac followed by BNT162b2.