Effectiveness of inactivated SARS-CoV-2 vaccines against the Delta variant infection in Guangzhou: a test-negative case–control real-world study

Figures & data

Figure 1. Flowchart of selection of study participants.

Table 1. Characteristics of all the cases identified in the outbreak in Guangzhou.

	Overall (n = 153)	Vaccinated (n = 38)	Unvaccinated (n = 115)	p-Value
Age
Median [IQR]	48.0 [30.0, 67.0]	45.5 [39.5, 51.7]	56.0 [21.5, 71.5]	0.157
Age group (years)				<0.001
≤17	26 (17.0%)	0	26 (22.6%)
18∼59	74 (48.4%)	37 (97.4%)	37 (32.2%)
≥60	53 (34.6%)	1 (2.6%)	52 (45.2%)
Gender				0.806
Male	63 (41.2%)	15 (39.5%)	48 (41.7%)
Female	90 (58.8%)	23 (60.5%)	67 (58.3%)
Clinical severity				0.009
Mild	32 (21.0%)	6 (15.8%)	26 (22.6%)
Moderate	105 (68.6%)	32 (84.2%)	73 (63.5%)
Severe	6 (3.9%)	0	6 (5.2%)
Critical	10 (6.5%)	0	10 (8.7%)
Time from symptom onset to viral RNA detection, days				0.957
−3 to 0	91 (59.5%)	23 (60.5%)	68 (59.1%)
1–3	47 (30.7%)	11 (29.0%)	36 (31.3%)
≥4	15 (9.8%)	4 (10.5%)	11 (9.6%)
Time from vaccination to symptom onset, days (Median, IQR)	29 (17.8∼57.0)	29 (17.8∼57.0)	–
Time from vaccination to hospitalisation, days				–
≤14	6 (15.8%)	6 (15.8%)	–
15–27	10 (26.3%)	10 (26.3%)	–
≥28	22 (57.9%)	22 (57.9%)	–
Time from onset to clinical cure, days				0.079
≤10	4 (2.6%)	0	4 (3.48%)
11–19	48 (31.4%)	17 (44.7%)	31 (27.0%)
≥20	101 (66.0%)	21 (55.3%)	80 (69.7%)
PCR cycle threshold (ct value)				0.226
<24	74 (48.4%)	17 (44.7%)	57 (49.6%)
24–40	62 (40.5%)	20 (52.6%)	42 (36.5%)
Symptoms
Fever	61 (39.87%)	20 (52.6%)	41 (47.4%)	0.064
Cough	41 (26.8%)	12 (31.6%)	29 (25.2%)	0.443

Note: p-Values were estimated by χ² tests or t-test. The “–” indicated no data.

Time from vaccination to hospitalisation: Some of the patients in our study were hospitalized after the onset of illness, and the remaining were hospitalized after large-scale nucleic acid screening (who might not have developed clinical symptoms at screening) for once the cases were confirmed as SARS-CoV-2 positive, admission to the designated hospital was mandatory.

Table 2. Characteristics of SARS-CoV-2 cases and controls for vaccine effectiveness estimation.

	Test-positive cases (n = 74)	Test-negative controls (n = 292)	p Value
Age
Median [IQR]	44.0 [36.2, 51.7]	39.0 [27.0, 48.0]	0.005
Age group (years)			0.055
18–29	12 (16.3%)	88 (30.1%)
30–45	32 (43.2%)	108 (37.0%)
46–59	30 (40.5%)	96 (32.9%)
Gender			0.001
Male	29 (39.2%)	177 (60.6%)
Female	45 (60.8%)	115 (39.4%)
Clinical severity
Mild	12 (16.2%)	–
Common	60 (81.1%)	–
Severe	2 (2.7%)	–
Critical	0	–
SARS-CoV-2 vaccination history			0.024
Unvaccinated	37 (50.0%)	107 (36.6%)
1 dose < 14 days	7 (9.5%)	40 (13.7%)
1 dose ≥ 14 days	18 (24.3%)	48 (16.4%)
2 doses < 14 days	2 (2.7%)	18 (6.2%)
2 doses ≥ 14 days	10 (13.5%)	79 (27.1%)

Note: p-Values were estimated by χ² tests or t-test. The “–” indicated no data.

Figure 2. Effectiveness of the inactivated vaccines against different severity of COVID-19 associated with the Delta variant strain. (A) Effectiveness in the whole population. The abscissa is VE (%) and the ordinate are different severity of clinical manifestations. The bars represent the estimated value of VE. Different colors indicate different vaccination doses. (B) Effectiveness in the study participants aged 18–39 years. (C) Effectiveness in study participants aged 40–59 years. (D) Effectiveness in males. (E) Effectiveness in females.

Table 3. Estimates of the association between vaccination and SARS-CoV-2 infection and effectiveness of inactivated SARS-CoV-2 vaccines.

	Vaccinated	Unvaccinated	1 dose ORadj (95%CI)	1 dose VEadj (%, 95%CI)	Vaccinated	Unvaccinated	2 doses ORadj (95%CI)	2 doses VEadj (%, 95%CI)
The whole population
Control	66	147	Reference	–	79	147	Reference	–
Overall cases	20	44	0.86 (0.45–1.60)	13.8 (−60.2, 54.8)	10	44	0.41 (0.19–0.84)	59.0 (16.0, 81.6)
Mild cases	2	6	1.13 (0.16–5.53)	−13.4 (−452.5, 84.3)	4	6	1.29 (0.32–4.69)	−29.4 (−369.4, 67.9)
Moderate cases	18	36	0.89 (0.45–1.73)	11.2 (−72.5, 55.5)	6	36	0.30 (0.11–0.70)	70.2 (29.6, 89.3)
Severe cases	0	2	–	–	0	2	–	100
18–39 years
Control	28	86	Reference	–	39	86	Reference	–
Overall cases	4	18	0.63 (0.17–1.90)	36.9 (−89.9, 83.1)	5	18	0.63 (0.20–1.74)	37.0 (−73.9, 80.5)
Mild cases	2	5	1.54 (0.21–8.14)	−53.7 (−714.3, 79.5)	2	5	0.91 (0.13–4.47)	9.3 (−346.9, 87.5)
Moderate cases	2	13	0.38 (0.06–1.54)	62.2 (−54.1, 94.5)	3	13	0.54 (0.12–1.85)	46.1 (−85.2, 88.4)
Severe cases	0	0	–	–	0	0	–	–
40–59 years
Control	38	61	Reference	–	40	61	Reference	–
Overall cases	16	26	0.98 (0.44–2.15)	1.8 (−115.3, 56.0)	5	26	0.26 (0.08–0.76)	72.5 (23.9–91.6)
Mild cases	0	1	–	–	2	1	2.62 (0.23–59.03)	−161.9 (−5803.3, 76.8)
Moderate cases	16	23	1.11 (0.49–2.47)	−11.0 (−147.3, 50.8)	3	23	0.19 (0.04–0.63)	80.6 (37.1, 95.7)
Severe cases	0	2	–	–	0	2	–	100
Males^a
Control	40	91	Reference	–	46	91	Reference	–
Overall cases	7	17	0.89 (0.32–2.27)	11.2 (−126.7, 68.2)	5	17	0.58 (0.18–1.58)	41.9 (−57.5, 81.8)
Mild cases	1	4	0.72 (0.04–5.39)	27.8 (−438.9, 96.4)	2	4	1.00 (0.13–5.37)	−0.1 (−437.4, 86.6)
Moderate cases	6	13	0.93 (0.30–2.58)	7.2 (−157.6, 69.8)	3	13	0.45 (0.10–1.49)	54.8 (−49.2, 90.0)
Severe cases	0	0	–	–	0	0	–	–
Females^a
Control	26	56	Reference	–	33	56	Reference	–
Overall cases	13	27	0.85 (0.36–1.98)	14.6 (−97.8, 64.3)	5	27	0.30 (0.09–0.82)	70.4 (18.4, 91.0)
Mild cases	1	2	1.08 (0.05–11.74)	−8.0 (−1074.0, 95.0)	2	2	1.78 (0.20–15.76)	−78.4 (−1476.2, 79.7)
Moderate cases	12	23	0.87 (0.35–2.11)	13.2 (−111.2, 65.5)	3	23	0.21 (0.05–0.69)	79.1 (30.9, 95.4)
Severe cases	0	2	–	–	0	2	–	100

Note: OR were adjusted for age and gender. The “–” indicated no data.

^a OR only adjusted for age.