Table 2. Univariate analysis on the associated factors of SARS-CoV-2 reinfection, according to primary infection strain (n=368).
| Factor | Wild type infection, n (%) (N=68) | Alpha/Delta infection, n (%) (N=88) | Omicron infection, n (%) (N=212) | |||||||||||||||||
| Reinfection cases | Non-reinfection cases | χ 2 | P | Reinfection cases | Non-reinfection cases | χ 2 | P | Reinfection cases | Non-reinfection cases | χ 2 | P | |||||||||
| Confirmed case | Probable case | Sub-total | Confirmed case | Probable case | Sub-total | Confirmed case | Probable case | Sub-total | ||||||||||||
| Note: “−” means not applicable. Abbreviation: SARS-CoV-2=severe acute respiratory syndrome coronavirus 2. * The interval between non-cases is the time from the first infection to the investigation date. † Only 325 respondents had access to detailed vaccination information. | ||||||||||||||||||||
| Gender | ||||||||||||||||||||
| Male | 11 (30.6) | 4 (11.1) | 15 (41.7) | 21 (58.3) | 2.13 | 0.145 | 14 (31.1) | 2 (4.4) | 16 (35.6) | 29 (64.4) | 0.01 | 0.947 | 9 (8.8) | 13 (12.7) | 22 (21.6) | 80 (78.4) | 1.32 | 0.251 | ||
| Female | 16 (50.0) | 3 (9.4) | 19 (59.4) | 13 (40.6) | 11 (25.6) | 4 (9.3) | 15 (34.9) | 28 (65.1) | 9 (8.2) | 8 (7.3) | 17 (15.5) | 93 (84.5) | ||||||||
| Age, years | ||||||||||||||||||||
| 0–17 | 0 (0) | 1 (14.3) | 1 (14.3) | 6 (85.7) | 9.04 | 0.011 | 4 (28.6) | 0 (0) | 4 (28.6) | 10 (71.4) | 3.50 | 0.173 | 1 (5.6) | 2 (11.1) | 3 (16.7) | 15 (83.3) | 0.74 | 0.692 | ||
| 18–59 | 25 (51.0) | 5 (10.2) | 30 (61.2) | 19 (38.8) | 17 (33.3) | 5 (9.8) | 22 (43.1) | 29 (56.9) | 16 (8.7) | 19 (10.4) | 35 (19.1) | 148 (80.9) | ||||||||
| ≥60 | 2 (16.7) | 1 (8.3) | 3 (25.0) | 9 (75.0) | 4 (17.4) | 1 (4.3) | 5 (21.7) | 18 (78.3) | 1 (9.1) | 0 (0) | 1 (9.1) | 10 (90.9) | ||||||||
| Occupation | ||||||||||||||||||||
| Medical worker | 4 (100.0) | 0 (0) | 4 (100.0) | 0 (0) | 2.39 | 0.122 | 1 (33.3) | 0 (0) | 1 (33.3) | 2 (66.7) | 0.30 | 0.586 | 5 (25.0) | 4 (20.0) | 9 (45.0) | 11 (55.0) | 8.55 | 0.004 | ||
| Other | 23 (35.9) | 7 (10.9) | 30 (46.9) | 34 (53.1) | 24 (28.2) | 6 (7.1) | 30 (35.3) | 55 (64.7) | 13 (6.8) | 17 (8.9) | 30 (15.6) | 162 (84.4) | ||||||||
| Clinical manifestation of primary infection | ||||||||||||||||||||
| Asymptomatic | 6 (46.2) | 2 (15.4) | 8 (61.5) | 5 (38.5) | 0.86 | 0.355 | 6 (42.9) | 2 (14.3) | 8 (57.1) | 6 (42.9) | 2.46 | 0.117 | 2 (4.3) | 6 (12.8) | 8 (17.0) | 39 (83.0) | 0.08 | 0.783 | ||
| Symptomatic | 21 (38.2) | 5 (9.1) | 26 (47.3) | 29 (52.7) | 19 (25.7) | 4 (5.4) | 23 (31.1) | 51 (68.9) | 16 (9.7) | 15 (9.1) | 31 (18.8) | 134 (81.2) | ||||||||
| Interval since last infection* | ||||||||||||||||||||
| 3 to 6 months | 0 (0) | 0 (0) | 0 (0) | 0 (0) | − | − | 0 (0) | 0 (0) | 0 (0) | 0 (0) | − | − | 0 (0) | 1 (4.0) | 1 (4.0) | 24 (96.0) | 2.90 | 0.089 | ||
| >6 months | 27 (39.7) | 7 (10.3) | 34 (50.0) | 34 (50.0) | 25 (28.4) | 6 (6.8) | 31 (35.2) | 57 (64.8) | 18 (9.6) | 20 (10.7) | 38 (20.3) | 149 (79.7) | ||||||||
| Interval since last vaccination† | ||||||||||||||||||||
| Unvaccinated | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0.02 | 0.893 | 1 (25.0) | 0 (0) | 1 (25.0) | 3 (75.0) | 2.22 | 0.329 | 0 (0) | 1 (25.0) | 1 (25.0) | 3 (75.0) | 0.06 | 0.972 | ||
| <12 months | 11 (42.3) | 2 (7.7) | 13 (50.0) | 13 (50.0) | 23 (31.1) | 5 (6.8) | 28 (37.8) | 46 (62.2) | 4 (8.0) | 6 (12.0) | 10 (20.0) | 40 (80.0) | ||||||||
| ≥12 months | 9 (33.3) | 4 (14.8) | 13 (48.1) | 14 (51.9) | 1 (12.5) | 0 (0) | 1 (12.5) | 7 (87.5) | 14 (10.6) | 13 (9.8) | 27 (20.5) | 105 (79.5) | ||||||||