Table 3. Estimated Effectiveness of mRNA Vaccines among Health Care Personnel, According to Covid-19 Vaccination Status among Case and Control Participants.*.
| Variable | Case Participants (N=1472) |
Control Participants (N=3420) |
Vaccine Effectiveness (95% CI) | |
|---|---|---|---|---|
| Unadjusted Analysis | Adjusted Analysis† | |||
| number (percent) | percent | |||
| Receipt of any Covid-19 vaccine | ||||
| One dose <10 days before test date | 249 (17) | 375 (11) | 25.0 (7.3 to 39.3) | 12.8 (−9.4 to 30.5) |
| One dose 10–13 days before test date | 104 (7) | 220 (6) | 44.1 (26.2 to 57.7) | 36.8 (14.8 to 53.1) |
| Partial vaccination | 140 (10) | 863 (25) | 81.3 (76.5 to 85.1) | 79.7 (74.1 to 84.1) |
| Complete vaccination | 167 (11) | 1072 (31) | 90.2 (87.0 to 92.6) | 90.4 (87.0 to 92.9) |
| BNT162b2 vaccine | ||||
| Partial vaccination | 122 (8) | 707 (21) | 79.4 (73.7 to 83.9) | 77.6 (70.9 to 82.7) |
| Complete vaccination | 149 (10) | 882 (26) | 88.9 (85.1 to 91.7) | 88.8 (84.6 to 91.8) |
| mRNA-1273 vaccine | ||||
| Partial vaccination | 18 (1) | 156 (5) | 89.8 (81.1 to 94.4) | 88.9 (78.7 to 94.2) |
| Complete vaccination | 18 (1) | 190 (6) | 95.7 (90.4 to 98.0) | 96.3 (91.3 to 98.4) |
Effectiveness of the messenger RNA (mRNA) vaccines was calculated as 1 minus the matched odds ratio (×100%) for partial or complete vaccination, as compared with no vaccination, and was estimated with the use of a conditional logistic-regression model with accounting for matching according to site of enrollment and week of test date. Vaccine effectiveness for all categories was estimated with the use of unvaccinated participants as a reference group. For partial vaccination, the effectiveness of a single dose was assessed during the interval from 14 days after receipt of the first dose through 6 days after receipt of the second dose. For complete vaccination, the effectiveness of two doses was assessed at least 7 days after receipt of the second dose (consistent with the Pfizer–BioNTech clinical trial7). CI denotes confidence interval.
The odds ratio was adjusted for age, race and ethnic group, presence of underlying conditions, and close contact with patients with Covid-19 in the workplace or persons with Covid-19 outside the workplace.