Table 2.
Seroprevalence of SARS-CoV-2 anti-spike or anti-nucleocapsid immunoglobulin G and risk factors for seropositivity in Gauteng Province stratified by sex, age group, and district.
| Pre-BA.1-Dominant Wave Serosurvey 1 | Post-BA.1-Dominant Wave Serosurvey | |||
|---|---|---|---|---|
| Category | Number Sampled N (%) | Seroprevalence 2 n (%; 95% CI 3) (%; 95% CI) |
Number Sampled N (%) | Seroprevalence 2 n (%; 95% CI 3) |
| All participants | 7010 | 5124 (73.1; 72.0–74.1) | 7510 | 6823 (90.9; 90.2–91.5) |
| Sex | ||||
| Male | 2941 (42%) | 1999 (68; 66.3–69.6) | 3096 (41.4%) | 2726 (88; 86.9–89.1) |
| Female | 4065 (58%) | 3123 (76.8; 75.5–78.1) | 4390 (58.6%) | 4075 (92.8; 92.0–93.6) |
| Age group–years | ||||
| <12 | 753 (10.7%) | 423 (56.2; 52.6–59.7) | 584 (7.8%) | 491 (84.1; 80.9–86.8) |
| 12–18 | 622 (8.9%) | 459 (73.8; 70.2–77.1) | 553 (7.4%) | 523 (94.6; 92.4–96.2) |
| >18 to 50 | 4047 (57.7%) | 2978 (73.6; 72.2–74.9) | 4614 (61.6%) | 4204 (91.1; 90.3–91.9) |
| >50 | 1588 (22.7%) | 1264 (79.6; 77.5–81.5) | 1739 (23.2%) | 1587 (91.3; 89.8–92.5) |
| Vaccination status | ||||
| Not vaccinated (all age groups) | 4938 (70.4%) | 3473 (70.3; 69.0–71.6) | 4891 (65.5%) | 4377 (89.5; 88.6–90.3) |
| Vaccinated | 1319 (18.8%) | 1228 (93.1; 91.6–94.3) | 1995 (26.7%) | 1918 (96.1; 95.2–96.9) |
| <12 yrs | 753 (10.7%) | 423 (56.2; 52.6–59.7) | 584 (7.8%) | 491 (84.1; 80.9–86.8) |
| Vaccination by age group | ||||
| <12 unvaccinated | 753 (10.7%) | 423 (56.2; 52.6–59.7) | 584 (7.8%) | 491 (84.1; 80.9–86.8) |
| 12–18 unvaccinated | 603 (8.6%) | 443 (73.5; 69.8–76.8) | 442 (5.9%) | 412 (93.2; 90.5–95.2) |
| 12–18 vaccinated | 19 (0.3%) | 16 (84.2; 62.4–94.5) | 106 (1.4%) | 106 (100; 96.5–100.0) |
| >18 to 50 unvaccinated | 3356 (47.9%) | 2335 (69.6; 68.0–71.1) | 3470 (46.5%) | 3109 (89.6; 88.5–90.6) |
| >18 to 50 vaccinated | 691 (9.9%) | 643 (93.1; 90.9–94.7) | 1130 (15.1%) | 1082 (95.8; 94.4–96.8) |
| >50 unvaccinated | 979 (14%) | 695 (71; 68.1–73.7) | 979 (13.1%) | 856 (87.4; 85.2–89.4) |
| >50 vaccinated | 609 (8.7%) | 569 (93.4; 91.2–95.1) | 759 (10.2%) | 730 (96.2; 94.6–97.3) |
| Reported previous COVID-19-positive test | ||||
| Never tested | 5956 (85%) | 4272 (71.7; 70.6–72.9) | 7209 (96.4%) | 6547 (90.8; 90.1–91.5) |
| Tested positive | 195 (2.8%) | 172 (88.2; 82.9–92.0) | 43 (0.6%) | 43 (100; 91.8–100.0) |
| Tested negative | 859 (12.3%) | 680 (79.2; 76.3–81.7) | 229 (3.1%) | 207 (90.4; 85.9–93.6) |
| Smoking status | ||||
| Non-smoker | 4086 (58.3%) | 3172 (77.6; 76.3–78.9) | 4336 (58%) | 3986 (91.9; 91.1–92.7) |
| Daily | 1115 (15.9%) | 741 (66.5; 63.6–69.2) | 1331 (17.8%) | 1173 (88.1; 86.3–89.8) |
| Once or twice a week | 238 (3.4%) | 178 (74.8; 68.9–79.9) | 393 (5.3%) | 361 (91.9; 88.7–94.2) |
| Occasionally | 196 (2.8%) | 151 (77; 70.7–82.4) | 278 (3.7%) | 257 (92.4; 88.7–95.0) |
| <18 yrs | 1375 (19.6%) | 882 (64.1; 61.6–66.6) | 1137 (15.2%) | 1014 (89.2; 87.2–90.9) |
| Comorbidities | ||||
| None | 4631 (66.1%) | 3432 (74.1; 72.8–75.4) | 5233 (70%) | 4758 (90.9; 90.1–91.7) |
| 1 or more | 1004 (14.3%) | 810 (80.7; 78.1–83.0) | 1111 (14.9%) | 1025 (92.3; 90.5–93.7) |
| <18 yrs (not assessed) | 1375 (19.6%) | 882 (64.1; 61.6–66.6) | 1137 (15.2%) | 1014 (89.2; 87.2–90.9) |
| HIV status | ||||
| HIV-negative | 6460 (92.2%) | 4728 (73.2; 72.1–74.3) | 6850 (91.6%) | 6232 (91; 90.3–91.6) |
| HIV-positive | 550 (7.8%) | 396 (72; 68.1–75.6) | 631 (8.4%) | 565 (89.5; 86.9–91.7) |
Note: Missing in current serosurvey 3: sex = 24; age group = 20; vaccination status = 40; ever tested COVID = 29, smoke = 35; co-morbidities = 29, and self-reported HIV = 29. Missing in previous serosurvey 2: sex = 4. n, number with outcome. N, denominator of population sampled. 1 Madhi et al., 2022 [10]. 2 Seroprevalence was defined as seropositive for anti-S or anti-N IgG, irrespective of vaccination status. 3 CI, confidence interval; confidence intervals have not been adjusted for multiplicity and should not be used for inference.