Table 2.
IRR and protective immunity of previous SARS-CoV-2 infection and vaccination against medically attended symptomatic omicron BA.4, BA.5, and XBB reinfection
|
Omicron BA.4 or BA.5 |
Omicron XBB |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Person-days at risk | Number of cases | Incidence per million person-days | IRR* (95% CI) | Protective immunity† (95% CI) | Person-days at risk | Number of cases | Incidence per million person-days | IRR* (95% CI) | Protective immunity† (95% CI) | ||
| SARS-CoV-2-naive | 53 076 623 | 3298 | 62·1 | 1·00 (reference value) | Reference | 24 498 337 | 36 510 | 1490 | 1·00 (reference value) | Reference | |
| Pre-omicron | |||||||||||
| Unvaccinated or partially vaccinated (0 or 1 dose) | 134 615 | 7 | 52·0 | 2·00 (0·90 to 4·43) | .. | 62 426 | 56 | 897 | 2·81 (2·11 to 3·75) | .. | |
| Completed primary series | 489 732 | 20 | 40·8 | 1·08 (0·66 to 1·79) | .. | 226 313 | 313 | 1383 | 1·82 (1·58 to 2·08) | .. | |
| Boosted | 2 777 207 | 134 | 48·2 | 0·87 (0·73 to 1·05) | 13% (−5 to 27) | 1 277 769 | 2369 | 1854 | 1·29 (1·23 to 1·35) | .. | |
| Omicron BA.1 | |||||||||||
| Unvaccinated or partially vaccinated (0 or 1 dose) | 63 887 | 5 | 78·3 | 2·77 (1·10 to 6·99) | .. | 29 701 | 23 | 774 | 2·43 (1·59 to 3·72) | .. | |
| Completed primary series | 662 962 | 12 | 18·1 | 0·45 (0·24 to 0·83) | 55% (17 to 76) | 308 506 | 243 | 788 | 0·97 (0·84 to 1·13) | 3% (−13 to 16) | |
| Boosted | 5 903 384 | 146 | 24·7 | 0·39 (0·33 to 0·46) | 61% (54 to 67) | 2 738 726 | 3034 | 1108 | 0·70 (0·68 to 0·73) | 30% (27 to 32) | |
| Omicron BA.2 | |||||||||||
| Unvaccinated or partially vaccinated (0 or 1 dose) | 117 811 | 6 | 50·9 | 2·07 (0·88 to 4·87) | .. | 55 004 | 28 | 509 | 1·80 (1·22 to 2·66) | .. | |
| Completed primary series | 782 089 | 6 | 7·7 | 0·20 (0·09 to 0·47) | 80% (53 to 91) | 365 077 | 214 | 586 | 0·78 (0·67 to 0·91) | 22% (9 to 33) | |
| Boosted | 12 772 414 | 150 | 11·7 | 0·22 (0·18 to 0·26) | 78% (74 to 82) | 5 969 416 | 3963 | 664 | 0·49 (0·47 to 0·51) | 51% (49 to 53) | |
IRR=incidence rate ratio.
*
Adjusted for age, sex, ethnicity, housing type, calendar date, vaccination status of SARS-CoV-2-naive group, days since last vaccine dose, and days since previous infection.
†
Negative protective immunity estimates are not presented.