Table 2. Effectiveness of mRNA Vaccines in Preventing SARS-CoV-2 Infection with Full and Partial Vaccination.*.
| Characteristic and Vaccination Status | Contributing Participants† | Person-Days | SARS-CoV-2 Infections | Vaccine Effectiveness‡ | ||
|---|---|---|---|---|---|---|
| Unadjusted | Adjusted | |||||
| no. | total no. | median (IQR) | no. | percent (95% CI) | ||
| Overall | ||||||
| Unvaccinated | 3964 | 127,971 | 19 (8–41) | 156 | — | — |
| Partially vaccinated | 3001 | 81,168 | 22 (21–28) | 11 | 86 (74–93) | 81 (64–90) |
| Fully vaccinated | 2510 | 161,613 | 69 (53–81) | 5 | 92 (80–97) | 91 (76–97) |
| mRNA vaccine product | ||||||
| BNT162b2 vaccine | ||||||
| Unvaccinated | 3964 | 127,971 | 19 (8–41) | 156 | — | — |
| Partially vaccinated | 2005 | 49,516 | 21 (21–22) | 8 | 85 (69–93) | 80 (60–90) |
| Fully vaccinated | 1731 | 120,653 | 77 (64–82) | 3 | 94 (82–98) | 93 (78–98) |
| mRNA-1273 vaccine | ||||||
| Unvaccinated | 3964 | 127,971 | 19 (8–41) | 156 | — | — |
| Partially vaccinated | 982 | 31,231 | 28 (28–31) | 3 | 88 (61–96) | 83 (40–95) |
| Fully vaccinated | 770 | 40,394 | 58 (44–66) | 2 | 84 (31–96) | 82 (20–96) |
| Age group | ||||||
| <50 yr | ||||||
| Unvaccinated | 2838 | 90,768 | 18 (8–42) | 107 | — | — |
| Partially vaccinated | 2116 | 57,064 | 22 (21–28) | 8 | 87 (72–94) | 81 (59–91) |
| Fully vaccinated | 1760 | 114,676 | 72 (55–81) | 4 | 91 (75–97) | 90 (69–97) |
| ≥50 yr | ||||||
| Unvaccinated | 1126 | 37,203 | 21 (9–40) | 49 | — | — |
| Partially vaccinated | 885 | 24,104 | 22 (21–28) | 3 | 84 (46–95) | 78 (28–93) |
| Fully vaccinated | 750 | 46,937 | 68 (50–80) | 1 | 95 (59–99) | 94 (51–99) |
At the time of specimen collection, participants were considered to be fully vaccinated (≥14 days after dose 2), partially vaccinated (≥14 days after dose 1 and <14 days after dose 2), or unvaccinated or to have indeterminate vaccination status (<14 days after dose 1). The 32 participants with SARS-CoV-2 infection who had indeterminate vaccination status were excluded, as were all person-days associated with indeterminate vaccination status.
The number of contributing participants does not equal the total number of participants in the study because contributing participants were required to be in active surveillance and to have met the vaccination criteria.
Vaccine effectiveness was calculated with the following formula: 100%×(1−hazard ratio for SARS-CoV-2 infection in vaccinated vs. unvaccinated participants). Adjusted vaccine effectiveness was inversely weighted for the propensity to be vaccinated, with doubly robust adjustment for local viral circulation, site, and occupation.