Table 2. Incidence Rate Ratios and Booster Effectiveness of Confirmed Infections According to Vaccine Type, Vaccine Combination, and Number of Days After Last Vaccine Dose During Omicron Wave.
| Vaccine group | Time since last dose, d | Person-days at risk | Infections, No. | Univariate | Multivariate | ||||
|---|---|---|---|---|---|---|---|---|---|
| Risk infection, IRR (95% CI)a | Estimated booster effectiveness, % (95% CI) | P value | Risk infection, IRR (95% CI)b | Estimated booster effectiveness, % (95% CI)b | P value | ||||
| PP/MM | 15-60 | 863 483 | 743 | 0.66 (0.61-0.71) | NA | <.001 | 0.67 (0.62-0.72) | NA | <.001 |
| PP/MM | 61-120 | 3 910 455 | 4703 | 0.86 (0.83-0.90) | NA | <.001 | 0.88 (0.84-0.91) | NA | <.001 |
| PP/MM | 121-150 | 7 221 831 | 7218 | 1 [Reference] | NA | NA | 1 [Reference] | NA | NA |
| PP/MM | 151-240 | 17 800 226 | 35 379 | 1.16 (1.13-1.19) | NA | <.001 | 1.16 (1.13-1.19) | NA | <.001 |
| PP/MM | 241-330 | 1 991 028 | 3364 | 1.16 (1.11-1.20) | NA | <.001 | 1.25 (1.20-1.31) | NA | <.001 |
| PPP | 15-60 | 24 664 888 | 35 831 | 0.68 (0.66-0.70) | 32.2 (30.5-33.9) | <.001 | 0.68 (0.67-0.70) | 31.7 (30.0-33.4) | <.001 |
| PPP | 61-120 | 45 086 042 | 73 191 | 0.82 (0.80-0.84) | 18.4 (16.4-20.3) | <.001 | 0.88 (0.86-0.90) | 11.9 (9.71-14.0) | <.001 |
| PPP | 121-330 | 20 457 351 | 72 447 | 0.90 (0.88-0.92) | 9.96 (7.73-12.1) | <.001 | 1.03 (1.00-1.05) | −2.83 (−5.43–0.287) | .03 |
| MMM | 15-60 | 7 324 592 | 8591 | 0.61 (0.59-0.63) | 39.3 (37.4-41.2) | <.001 | 0.58 (0.57-0.61) | 41.3 (39.4-43.1) | <.001 |
| MMM | 61-120 | 8 312 353 | 16 828 | 0.70 (0.68-0.72) | 30.3 (28.4-32.2) | <.001 | 0.74 (0.72-0.76) | 26.3 (24.2-28.3) | <.001 |
| MMM | 121-330 | 1 073 471 | 3440 | 0.77 (0.74-0.80) | 23.0 (19.8-26.0) | <.001 | 0.85 (0.82-0.89) | 14.6 (11.0-18.0) | <.001 |
| PPM | 15-60 | 7 403 155 | 11 065 | 0.65 (0.63-0.67) | 34.9 (32.9-36.8) | <.001 | 0.65 (0.63-0.67) | 34.9 (33.0-36.8) | <.001 |
| PPM | 61-120 | 6 341 973 | 13 025 | 0.73 (0.71-0.76) | 26.6 (24.5-28.7) | <.001 | 0.82 (0.79-0.84) | 18.3 (15.9-20.7) | <.001 |
| PPM | 121-330 | 1 370 351 | 4648 | 0.84 (0.80-0.87) | 16.5 (13.4-19.6) | <.001 | 0.96 (0.93-1.00) | 3.69 (0.03-7.21) | .048 |
| MMP | 15-60 | 2 354 758 | 3047 | 0.66 (0.64-0.69) | 33.6 (30.7-36.4) | <.001 | 0.64 (0.62-0.67) | 35.6 (32.8-38.3) | <.001 |
| MMP | 61-120 | 2 409 500 | 5 416 | 0.74 (0.71-0.76) | 26.3 (23.7-28.9) | <.001 | 0.77 (0.74-0.79) | 23.4 (20.7-26.1) | <.001 |
| MMP | 121-330 | 210 409 | 751 | 0.83 (0.77-0.89) | 17.3 (10.9-23.3) | <.001 | 0.90 (0.84-0.97) | 9.72 (2.66-16.3) | .008 |
| SS | 15-60 | 529 415 | 661 | 0.95 (0.88-1.03) | NA | .19 | 1.03 (0.95-1.11) | NA | .49 |
| SS | 61-120 | 1 016 233 | 2265 | 1.13 (1.08-1.18) | NA | <.001 | 1.25 (1.20-1.31) | NA | <.001 |
| SS | 121-330 | 103 071 | 249 | 0.96 (0.844-1.09) | NA | .50 | 1.09 (0.96-1.24) | NA | .18 |
| SSS | 15-60 | 1 366 994 | 2293 | 0.82 (0.79-0.86) | 17.6 (13.7-21.4) | <.001 | 0.93 (0.89-0.97) | 7.26 (2.79-11.5) | .002 |
| SSS | 61-330 | 977 370 | 2696 | 0.77 (0.74-0.81) | 23.0 (19.5-26.3) | <.001 | 0.88 (0.84-0.92) | 12.5 (8.54-16.3) | <.001 |
Abbreviations: IRR, incidence rate ratio; NA, not applicable; M, mRNA-1273 (Moderna); P, BNT162b2 (Pfizer-BioNTech); S, CoronaVac (Sinovac) or BBIBP-CorV (Sinopharm).
a
Univariate IRR was adjusted for calendar day to account for varying daily infection pressure.
b
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.