Table 3.
Mixed effects Cox proportional hazards model for death within 28 days from positive test for SARS-CoV-2 in the full cohort and the known variant cohort
|
Overall (n=2264, 259 clusters) |
Known variant cohort (n=937, 176 clusters) |
|||
|---|---|---|---|---|
| Adjusted HR (95% CI) | p value | Adjusted HR (95% CI) | p value | |
| Period or variant | ||||
| Pre-omicron (delta) | 1 (ref) | .. | 1 (ref) | .. |
| Omicron | 0·68 (0·44–1·04) | 0·076 | 0·61 (0·32–1·16) | 0·13 |
| Sex | ||||
| Male | 1 (ref) | .. | 1 (ref) | .. |
| Female | 0·54 (0·38–0·76) | <0·0001 | 0·65 (0·27–1·12) | 0·099 |
| Age | ||||
| Age (per year increase) | 1·04 (1·02–1·07) | <0·0001 | 1·04 (1·01–1·08) | 0·025 |
| Primary vaccine course* | ||||
| Unvaccinated | 1 (ref) | .. | 1 (ref) | .. |
| AstraZeneca (ChAdOx1) | 0·82 (0·49–1·36) | 0·61† | 0·63 (0·29–1·36) | 0·61† |
| Pfizer (BNT162b2) | 0·70 (0·39–1·24) | .. | 0·40 (0·15–1·03) | .. |
| Type not known | 0·63 (0·50–1·60) | .. | 0·56 (0·12–2·70) | .. |
| Booster vaccine status* | ||||
| No booster | 1 (ref) | .. | 1 (ref) | .. |
| Booster more than 1 week before positive test | 0·60 (0·38–0·93) | 0·023 | 0·55 (0·27–1·12) | 0·099 |
| Past infection status | ||||
| No past infection | 1 (ref) | .. | 1 (ref) | .. |
| Past infection | 0·90 (0·50–1·60) | 0·72 | 0·45 (0·11–1·86) | 0·27 |
Models are adjusted for median-centred age and all other variables listed in the model (sex, primary vaccine course, time from primary booster, history of previous infection) and have frailty term for long-term care facility clustering. HR=hazard ratio.
The adjusted HRs for boosting are the additional effects of boosting in those with primary vaccination—for example, the HR for an unboosted Pfizer recipient relative to an unvaccinated individual is 0·70, but for a boosted individual with initial Pfizer vaccination relative to an unvaccinated person is 0·70 × 0·60=0·42.
p value indicates difference between unvaccinated individuals and any vaccinated individual, regardless of which vaccine was administered.