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. 2025 Feb 7;153:e30. doi: 10.1017/S0950268825000172

Table 2.

Comparison of Omicron cases with one and two infections in Hong Kong from 31 December 2021 to 29 January 2023

N (%, 95%CI) Cases with one infection
2,891,019		 Cases with two infections
99,236		 P value
Female: Male 1.18: 1 1.30: 1 <0.001
  • • Female
 1,561,010 (54.00%, 53.94%–54.05%) 56,080 (56.51%, 56.20%–56.82%)
  • • Male
 1,317,858 (45.58%, 45.53%–45.64%) 43,136 (43.47%, 43.16%–43.78%)
• Sex information unavailable 12,151 (0.42%, 0.41%–0.43%) 20 (0.02%, 0.02%–0.03%)
Median age (Range, IQR), years 44 (0–112, 29–60) 43 (0–108, 29–62) <0.001
Age group, years <0.001
  • 0–9
 187,105 (6.47%, 6.44%–6.50%) 5,289 (5.33%, 5.19%–5.47%)
  • 10–19
 211,119 (7.30%, 7.27%–7.33%) 6,720 (6.77%, 6.62%–6.93%)
  • 20–29
 328,744 (11.37%, 11.33%–11.41%) 13,526 (13.63%, 13.42%–13.85%)
  • 30–39
 476,310 (16.48%, 16.43%–16.52%) 18,389 (18.53%, 18.29%–18.77%)
  • 40–49
 474,261 (16.40%, 16.36%–16.45%) 15,134 (15.25%, 15.03%–15.48%)
  • 50–59
 459,355 (15.89%, 15.85%–15.93%) 12,477 (12.57%, 12.37%–12.78%)
  • 60–69
 409,140 (14.15%, 14.11%–14.19%) 11,214 (11.30%, 11.10%–11.50%)
  • 70–79
 198,826 (6.88%, 6.85%–6.91%) 6,743 (6.79%, 6.64%–6.95%)
  • > = 80
 132,035 (4.57%, 4.54%–4.59%) 9,723 (9.80%, 9.61%–9.98%)
  • Age information unavailable
 14,124 (0.49%, 0.48%–0.50%) 21 (0.02%, 0.01%–0.03%)
Importation status at the last infection <0.001
  • • Local
 2,813,766 (97.33%, 97.31%–97.35%) 95,844 (96.58%, 96.47%–96.69%)
  • • Imported
 77,253 (2.67%, 2.65%–2.69%) 3,392 (3.42%, 3.31%–3.53%)
With available symptoms information at the last infection: 2,437,433 94,834 <0.001
  • • Symptomatic
 1,381,749 (56.69%, 56.63%–56.75%) 50,414 (53.16%, 52.84%–53.48%)
  • • Asymptomatic
 1,055,684 (43.31%, 43.25%–43.37%) 44,420 (46.84%, 46.52%–47.16%)
Cases with chronic diseases 788,457 (27.27%, 27.22%–27.32%) 33,297 (33.55%, 33.26%–33.85%) <0.001
Residential care home (RCH) residents 40,669 (1.41%, 1.39%–1.42%) 11,138 (11.22%, 11.03%–11.42%) <0.001
Severe clinical outcomes at the last infection 16,817 (0.58%, 0.57%–0.59%) 559 (0.56%, 0.52%–0.61%) 0.500
  • Deaths
 9,914 (0.34%, 0.34%–0.35%) 146 (0.15%, 0.12%–0.17%) <0.001
Time interval between primary and the 2nd infection (median days) NA 31–371 days (281 days)
Vaccination ≥2 valid doses at the last infection 2,324,762 (80.41%, 80.37%–80.46%) 81,332 (81.96%, 81.72%–82.20%) <0.001
Vaccination ≥3 valid doses at the last infection 1,442,721 (49.90%, 49.85%–49.96%) 46,783 (47.14%, 46.83%–47.45%) <0.001

Note: The sub-cohort of Omicron cases referred to those individuals who were recruited (got the primary infection) after the start of Omicron wave (31 December 2021) in Hong Kong. NA: Not applicable; IQR: Interquartile range.