Table 3.
Effectiveness of COVID-19 vaccines against severe SARS-CoV-2 infection 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) | Adjusted odds ratioe(95% CI) | Vaccine effectiveness (%) (95% CI) | Power(%) |
|---|---|---|---|---|---|---|
| AZD1222 (Covishield)/ BBV152 (Covaxin) | (n = 1143) | (n = 2541) | ||||
| Unvaccinated | 815 (71.3) | 1116 (43.9) | 1 | 1 | ||
| Partial vaccinationa | 201 (17.6) | 714 (28.1) | 0.34 (0.29-0.41) | 0.35 (0.29-0.43) | 65 (57-71) | 100 |
| Complete vaccinationb | 94 (8.2) | 554 (21.8) | 0.20 (0.16-0.26) | 0.17 (0.13-0.22) | 83 (78-87) | 100 |
| Interval between 2 doses ( ≥14 days after second dose) - AZD1222(Covishield)/ BBV152 (Covaxin) | (n = 909) | (n = 1670) | ||||
| Unvaccinated | 815 (89.7) | 1116 (66.8) | 1 | 1 | ||
| <6 weeks | 75 (8.2) | 383 (22.9) | 0.24 (0.18 - 0.31) | 0.23 (0.17-0.31) | 77 (69 - 83) | 100 |
| 6-8 weeks | 8 (0.9) | 114 (6.8) | 0.08 (0.04 - 0.18) | 0.06 (0.03 - 0.14) | 94 (86-97) | 100 |
| 9-11 weeks | 7 (0.8) | 42 (2.5) | 0.19 (0.09 - 0.44) | 0.15 (0.06 - 0.34) | 85 (66 - 94) | 98.2 |
| ≥12 weeks | 4 (0.4) | 15 (0.9) | 0.28 (0.09 - 0.86) | 0.28 (0.09 - 0.88) | 72 (12-91) | 32.3 |
| AZD1222/Covishield | (n = 1072) | (n = 2263) | ||||
| Unvaccinated | 815 (76.0) | 1116 (49.3) | 1 | 1 | ||
| Partial vaccinationa | 172 (16.0) | 641 (28.3) | 0.32 (0.27-0.4) | 0.33 (0.27-0.41) | 67 (59-73) | 100 |
| Complete vaccinationb | 58 (5.4) | 388 (17.1) | 0.18 (0.13-0.24) | 0.15 (0.11-0.21) | 85 (79-89) | 100 |
| Interval between 2 doses ( ≥14 days after second dose) - AZD1222/Covishield | (n = 873) | (n = 1504) | ||||
| Unvaccinated | 815 (93.4)) | 1116 (74.2) | 1 | 1 | ||
| <6 weeks | 41 (4.7) | 236 (15.7) | 0.21 (0.15 - 0.30) | 0.19 (0.13 - 0.28) | 81 (72 - 87) | 100 |
| 6-8 weeks | 7 (0.8) | 102 (6.8) | 0.08 (0.04 - 0.18) | 0.06 (0.03 -0.14) | 94 (86 - 97) | 100 |
| 9-11 weeks | 6 (0.7) | 36 (2.4) | 0.19 (0.08 - 0.47) | 0.15 (0.06 - 0.37) | 85 (63 - 94) | 95.7 |
| ≥12 weeks | 4 (0.5) | 14 (0.9) | 0.30 (0.10 - 0.93) | 0.30 (0.10 - 0.95) | 70 (5 - 90) | 25.6 |
| BBV152/Covaxin | (n = 886) | (n = 1382) | ||||
| Unvaccinated | 815 (92.0) | 1116 (80.6) | 1 | 1 | ||
| Partial vaccinationa | 29 (3.3) | 71 (5.1) | 0.57 (0.36-0.90) | 0.61 (0.38-0.98) | 39 (2-62) | 72.9 |
| Complete vaccinationb | 36 (4.1) | 156 (11.3) | 0.30 (0.20-0.44) | 0.29 (0.19-0.43) | 71 (57-81) | 100 |
| Interval between 2 doses ( ≥14 days after second dose) - BBV152/Covaxin | (n = 851) | (n = 1272) | ||||
| Unvaccinated | 815 (95.8) | 1116 (87.7) | 1 | 1 | ||
| <6 weeks | 34 (4.0) | 137 (10.8) | 0.33 (0.22-0.49) | 0.33 (0.21-0.50) | 67 (50-79) | 100 |
| 6-8 weeks | 1 (0.1) | 12 (0.9) | 0.11 (0.01-0.85) | 0.07 (0.01-0.66) | 93 (34-99) | 61.4 |
| 9-11 weeks | 1 (0.1) | 6 (0.5) | 0.20 (0.02-1.70) | 0.14 (0.02-1.16) | 86 (0-98) | 15.4 |
| ≥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).
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.