Table 3.
Hazard of COVID-19 (healthcare workers relative to community referents) by infection wave adjusted for number of vaccines and/or number of PCR tests
| COVID-19 | ||||||
|---|---|---|---|---|---|---|
| From physician record | From PCR test | |||||
| HR | 95% CI | p-value | HR | 95% CI | p-value | |
| HCWs relative to controls by Wave* | ||||||
| 1: March–June 2020 | 1.30 | 1.17 to 1.45 | <0.001 | 1.67 | 0.60 to 4.61 | 0.323 |
| 2: July 2020–Feb 2021 | 1.31 | 1.15 to 1.50 | <0.001 | 0.51 | 0.37 to 0.71 | <0.001 |
| 3: March–June 2021 | 0.93 | 0.75 to 1.17 | 0.553 | 0.41 | 0.24 to 0.69 | 0.001 |
| 4: July–October 2021 | 0.78 | 0.55 to 1.10 | 0.158 | 0.77 | 0.52 to 1.14 | 0.196 |
| 5: Nov 2021–March 2022 | 1.31 | 1.03 to 1.66 | 0.026 | 2.45 | 2.00 to 3.01 | <0.001 |
| Number of vaccine doses | ||||||
| 0 | 1.00 | – | – | 1.00 | – | |
| 1 | 1.48 | 1.27 to 1.71 | <0.001 | 0.99 | 0.89 to 1.24 | 0.961 |
| 2 | 1.27 | 1.10 to 1.46 | 0.001 | 0.55 | 0.45 to 0.68 | <0.001 |
| 3 | 1.31 | 1.05 to 1.62 | 0.016 | 0.74 | 0.58 to 0.94 | 0.016 |
| 4 | 3.80 | 1.55 to 9.29 | 0.003 | 0.32 | 0.06 to 1.69 | 0.178 |
| Number of PCR tests | – | – | – | 6.45 | 6.09 to 6.83 | <0.001 |
| N observations | 102,145 | 152,140 | ||||
| Individuals | 17,505 | 17,505 | ||||
| Groups | 2959 | 2959 | ||||
| Number of failures | 4772 | 2288 | ||||
*Wave-specific hazard ratios of healthcare workers relative to community referents obtained from linear combinations in the multiple multilevel piecewise exponential proportional hazards regression model shown in Supplementary information