Table 4.
Incidence of SARS-CoV-2 from 4 June 2022 to 31 January 2023 (due to BA.4/5 and later subvariants) in those with and without RT-PCR confirmed SARS-CoV-2 infection prior to 30 September 2020 (early infection)
| Early Infection (EI) |
No Early Infection (non-EI) |
EI vs. non -EI IRR (95% CI) |
EI vs. Non-EI Hazard Ratio2 (95% CI) | |
|---|---|---|---|---|
| No BA.1/BA.2 infection | ||||
| Number of COVID-19 infections | 89 | 42 | ||
| Participant-days | 121,623 | 28,779 | ||
| COVID-19 rate/1000 participant days | 0.73 | 1.46 | 0.50 (0.35–0.72) | 0.47 (0.32–0.68) |
| With BA.1/BA.2 infection1 | ||||
| Number of COVID-19 infections | 4 | 5 | ||
| Participant-days | 20,665 | 9413 | ||
| COVID-19 rate/1000 participant days | 0.19 | 0.53 | 0.36 (0.10–1.36) | 0.20 (0.03–1.21) |
1Comparing participants with no early or BA.1/BA.2 infection (42 cases during 28779 participant days) to those with both an early infection and a BA.1/BA.2 infection (4 cases during 20665 participant days), the IRR is 0.13 (95%CI 0.04–0.34) and the hazard ratio is 0.07 (95%CI 0.03–0.21)
2Hazard ratios from the primary analysis: multivariable Cox regression adjusted for age, COVID-19 vaccination, severity of 2020 illness, neighborhood income quantile, ethnicity, education, work status during omicron and presence of children in the household