Table 3. Incidence Rate Ratios and Booster Effectiveness Estimates of Severe COVID-19 According to Vaccine Type, Vaccine Combination, and Time Since Last Vaccine Dose During Omicron Wave.
| Vaccine group | Time since last dose, d | Person-days at riska | Severe COVID-19, No. | Univariate | Multivariate | ||||
|---|---|---|---|---|---|---|---|---|---|
| Risk infection, IRR (95% CI)b | Booster effectiveness, % (95% CI) | P value | Risk infection, IRR (95% CI)c | Booster effectiveness, % (95% CI)c | P value | ||||
| PP/MM | 15-60 | 839 558 | 41 | 1.92 (1.35 to 2.72) | NA | <.001 | 1.16 (0.82 to 1.65) | NA | .40 |
| PP/MM | 61-120 | 3 772 331 | 158 | 1.57 (1.25 to 1.98) | NA | <.001 | 1.27 (1.01 to 1.59) | NA | .04 |
| PP/MM | 121-150 | 7 075 876 | 136 | 1 [Reference] | NA | NA | 1 [Reference] | NA | NA |
| PP/MM | 151-240 | 16 929 879 | 227 | 0.41 (0.33 to 0.50) | NA | <.001 | 0.83 (0.67 to 1.03) | NA | .09 |
| PP/MM | 241-330 | 1 918 398 | 49 | 0.90 (0.65 to 1.25) | NA | .53 | 0.78 (0.56 to 1.08) | NA | .13 |
| PPP | 15-60 | 22 808 781 | 69 | 0.07 (0.06 to 0.10) | 92.6 (90.1 to 94.5) | <.001 | 0.15 (0.11 to 0.20) | 85.2 (80.2 to 88.9) | <.001 |
| PPP | 61-120 | 42 090 860 | 210 | 0.13 (0.11 to 0.16) | 86.9 (83.7 to 89.4) | <.001 | 0.19 (0.15 to 0.24) | 81.0 (76.3 to 84.7) | <.001 |
| PPP | 121-330 | 16 220 264 | 244 | 0.186 (0.15 to 0.23) | 81.4 (76.9 to 85.0) | <.001 | 0.13 (0.10 to 0.16) | 87.3 (84.2 to 89.8) | <.001 |
| MMM | 15-60 | 6 922 113 | 2 | 0.01 (0.001 to 0.03) | 99.2 (96.9 to 99.8) | <.001 | 0.03 (0.01 to 0.10) | 97.5 (89.7 to 99.4) | <.001 |
| MMM | 61-120 | 7 317 875 | 10 | 0.02 (0.01 to 0.05) | 97.6 (95.4 to 98.7) | <.001 | 0.06 (0.03 to 0.12) | 93.8 (88.2 to 96.8) | <.001 |
| MMM | 121-330 | 716 656 | 10 | 0.16 (0.08 to 0.30) | 84.2 (69.8 to 91.7) | <.001 | 0.11 (0.058 to 0.21) | 89.0 (78.9 to 94.2) | <.001 |
| PPM | 15-60 | 6 906 443 | 7 | 0.02 (0.01 to 0.05) | 97.7 (95.2 to 98.9) | <.001 | 0.127 (0.06 to 0.27) | 87.3 (72.8 to 94.1) | <.001 |
| PPM | 61-120 | 5 512 680 | 11 | 0.04 (0.02 to 0.07) | 96.3 (93.2 to 98.0) | <.001 | 0.12 (0.06 to 0.22) | 88.0 (77.8 to 93.6) | <.001 |
| PPM | 121-330 | 1 030 897 | 15 | 0.17 (0.10 to 0.30) | 82.7 (70.4 to 89.9) | <.001 | 0.16 (0.09 to 0.27) | 84.4 (73.4 to 90.9) | <.001 |
| MMP | 15-60 | 2 216 635 | 0 | 0 (0 to ∞) | 1 (−∞ to 1) | .95 | 0 (0 to ∞) | 1 (−∞ to 1) | .95 |
| MMP | 61-120 | 2 100 563 | 6 | 0.0477 (0.0210 to 0.108) | 95.2 (89.2 to 97.9) | <.001 | 0.13 (0.06 to 0.30) | 87.0 (70.4 to 94.3) | <.001 |
| MMP | 121-330 | 122 192 | 2 | 0.17 (0.04 to 0.69) | 82.9 (30.6 to 95.8) | .01 | 0.14 (0.03 to 0.55) | 86.3 (44.7 to 96.6) | .005 |
| SS | 15-60 | 517 589 | 27 | 2.01 (1.33 to 3.03) | NA | <.001 | 1.81 (1.20 to 2.74) | NA | .005 |
| SS | 61-330 | 1 046 507 | 26 | 0.64 (0.42 to 0.97) | NA | .04 | 0.85 (0.56 to 1.29) | NA | .45 |
| SSS | 15-330 | 2 068 163 | 16 | 0.15 (0.09 to 0.25) | 85.0 (74.8 to 91.1) | <.001 | 0.30 (0.18 to 0.51) | 69.7 (48.9 to 82.0) | <.001 |
Abbreviations: IRR, incidence rate ratio; M, mRNA-1273 (Moderna); P, BNT162b2 (Pfizer-BioNTech); S, CoronaVac (Sinovac) or BBIBP-CorV (Sinopharm).
The person-days at risk for severe COVID-19 was less than that of confirmed infection as the final 7 days of data in the period under study were omitted from the severe COVID-19 analysis.
Univariate IRR was derived using model which adjusted for calendar day to account for varying daily infection pressure.
Multivariate analysis was adjusted for age, sex, race, housing status (surrogate for socioeconomic status), vaccine type and combination, number of days since the last dose and calendar day to account for varying daily infection pressure. Two-dose mRNA vaccine 121 to 150 days (5 months) after the second dose was the reference group.