Table 4.
Effectiveness of COVID-19 vaccines against severe SARS-CoV-2 infection by Delta variant in individuals aged >45 years by dose and time since vaccination, and interval between two doses, India, May - July 2021.
| Vaccination status | Casesc (%) | Controlsd(%) | Crude odds ratio (95% CI) | Adjuste dodds ratioe(95% CI) | Vaccine effectiveness (%) (95% CI) | Power(%) |
|---|---|---|---|---|---|---|
| AZD1222 (Covishield)/ BBV152 (Covaxin) | (n = 511) | (n = 2541) | ||||
| Unvaccinated | 368 (72.0) | 1116 (43.9) | 1 | 1 | ||
| Partial vaccinationa | 75 (14.7) | 714 (21.8) | 0.29 (0.22-0.38) | 0.29 (0.22-0.39) | 71 (61-78) | 100 |
| Complete vaccinationb | 46 (9.0) | 554 (21.8) | 0.23 (0.17-0.32) | 0.19 (0.14-0.28) | 81 (72-86) | 100 |
| Interval between 2 doses ( ≥14 days after second dose) of AZD1222 (Covishield)/ BBV152 (Covaxin) | (n = 414) | (n = 1670) | ||||
| Unvaccinated | 368 (88.9) | 1116 (66.8) | 1 | 1 | ||
| <6 weeks | 35 (8.4) | 383 (22.9) | 0.26 (0.18-0.39) | 0.24 (0.16-0.35) | 76 (65-84) | 100 |
| 6-8 weeks | 3 (0.7) | 114 (6.8) | 0.07 (0.02-0.23) | 0.06 (0.02-0.18) | 94 (82-98) | 100 |
| 9-11 weeks | 5 (1.2) | 42 (2.5) | 0.30 (0.12-0.77) | 0.20 (0.08-0.54) | 80 (46-92) | 55.6 |
| ≥12 weeks | 3 (0.7) | 15 (0.9) | 0.45 (0.13-1.62) | 0.41 (0.11-1.49) | 59 (0-89) | 3.4 |
| AZD1222/Covishield | (n = 476) | (n = 2263) | ||||
| Unvaccinated | 368(77.3) | 1116 (49.3) | 1 | 1 | ||
| Partial vaccinationa | 62 (13.0) | 641 (28.3) | 0.26 (0.19-0.35) | 0.26 (0.19-0.36) | 74 (64-81) | 100 |
| Complete vaccinationb | 26(5.5) | 388 (17.2) | 0.19 (0.12-0.29) | 0.15 (0.10-0.23) | 85 (77-90) | 100 |
| Interval between 2 doses( ≥14 days after second dose) of AZD1222/Covishield | (n = 394) | (n = 1504) | ||||
| Unvaccinated | 368 (93.4) | 1116 (74.1) | 1 | 1 | ||
| <6 weeks | 16 (4.1) | 236 (15.7) | 0.20 (0.12-0.34) | 0.17 (0.09-0.29) | 83 (71-91) | 100 |
| 6-8 weeks | 3 (0.8) | 102 (6.8) | 0.08 (0.02-0.26) | 0.06 (0.02-0.20) | 94 (80-98) | 100 |
| 9-11 weeks | 4 (1.0) | 36 (2.4) | 0.28 (0.10-0.81) | 0.19 (0.06-0.57) | 81 (43-94) | 47.3 |
| ≥12 weeks | 3 (0.8) | 14 (0.9) | 0.49 (0.14-1.76) | 0.43 (0.12-1.61) | 67 (0-88) | 1.3 |
| BBV152/Covaxin | (n = 403) | (n = 1384) | ||||
| Unvaccinated | 368 (91.3) | 1116 (80.6) | 1 | 1 | ||
| Partial vaccinationa | 13 (3.2) | 73 (5.3) | 0.60 (0.32-1.13) | 0.59 (0.30-1.13) | 41 (0-70) | 46.7 |
| Complete vaccinationb | 20 (5.0) | 156 (11.3) | 0.37 (0.22-0.61) | 0.34 (0.20-0.58) | 66 (42-80) | 99.3 |
| Interval between 2 doses ( ≥14 days after second dose) of BBV152/Covaxin | (n = 388) | (n=1272) | ||||
| Unvaccinated | 368 (94.8) | 1116 (87.7) | 1 | 1 | ||
| <6 weeks | 19 (4.9) | 137 (10.8) | 0.42 (0.25-0.70) | 0.40 (0.23-0.69) | 60 (31-77) | 96.2 |
| 6-8 weeks | 0 (0.0) | 12 (0.9) | - | - | - | - |
| 9-11 weeks | 1 (0.3) | 6 (0.5) | 0.41 (0.05-3.43) | 0.28 (0.03-2.35) | 72 (0-97) | 3.7 |
| ≥12 weeks | 0 (0.0) | 1 (0.1) | - | - | - | - |
Partial vaccination: One dose with an interval between second dose and COVID-19 testing/hospitalization ≥21 days.
Complete vaccination: Two doses with an interval between second dose and COVID-19 testing/hospitalization ≥14 days.
Case: Laboratory confirmed COVID-19 patients hospitalized with severe COVID-19 (One of the following: fever, cough, dyspnoea, fast breathing plus one of the following: respiratory rate > 30 breaths/min; severe respiratory distress; or SpO2 < 90% on room air) infected with Delta variant.
Control: RT-PCR negative individuals who remained negative up to 7 days after initial RT-PCR test.
Adjusted for age, any pre-existing comorbidities, participation in social/religious events, frequency of mask use, and rural/urban residence.