Table 1. Characteristics of SARS-CoV-2 Delta infected individuals and their close contacts in Hunan Province, China, 2021.
| Characteristics |
Infections
(n=129) |
Close contacts
(n=2,118) |
Secondary infection attack rate (%, 95% CI)* |
| Note: “−” means data not available.The last column provided the secondary infection attack rates across different groups of age, sex, and vaccination history. Abbreviation: IQR=interquartile range; CI=confidence interval; SARS-CoV-2=severe acute respiratory syndrome coronavirus 2; COVID-19=coronavirus disease 2019. * The secondary infection attack rate was calculated by dividing the number of infections by the total number of close contacts. † Vaccination history: 1) unvaccinated (i.e., individuals who did not receive any COVID-19 vaccines or received 1 dose of COVID-19 vaccine less than 14 days before the date of the last known contact); 2) partially vaccinated (i.e., individuals who had received either 1 dose of a COVID-19 vaccine or received 2 doses of vaccines with the date of the second dose less than 14 days before the date of the last known contact) and 3) fully vaccinated (i.e., individuals who completed the full 2-dose course vaccination more than 14 days before the date of the last known contact). § For the asymptomatic subjects and the cases diagnosed by imaging characteristics, we used the date of the first sample collection with a positive test instead of the date of symptom onset. | |||
| Age, years | |||
| Median (IQR) | 34 (15, 48) | 34 (20, 46) | |
| Age group, years | |||
| 0–9 | 19 (14.7%) | 140 (6.6%) | 10.7 (6.1, 17.1) |
| 10–17 | 19 (14.7%) | 293 (13.8%) | 4.8 (2.6, 7.9) |
| 18–64 | 87 (67.4%) | 1,595 (75.3%) | 3.2 (2.4, 4.2) |
| >65 | 4 (3.1%) | 90 (4.2%) | 4.4 (1.2, 11) |
| Sex | |||
| Male | 58 (45.0%) | 920 (43.4%) | 4.6 (3.3, 6.1) |
| Female | 71 (55.0%) | 1,198 (56.6%) | 3.5 (2.5, 4.7) |
| Clinical outcome | |||
| Not infected | − | 2,034 (96.0%) | |
| Confirmed asymptomatic infection | 19 (14.7%) | 9 (0.4%) | |
| Confirmed symptomatic infection | 110 (85.3%) | 75 (3.5%) | |
| Mild | 48 (43.6%) | 39 (52.0%) | |
| Moderate | 61 (55.5%) | 35 (46.7%) | |
| Severe | 1 (0.9%) | 1 (1.3%) | |
| Vaccination history† | |||
| Unvaccinated | 66 (51.2%) | 993 (46.9%) | 5.2 (3.9, 6.8) |
| Partially vaccinated | 27 (20.9%) | 290 (13.7%) | 4.8 (2.7, 8.0) |
| Time interval between last vaccination and symptoms onset or last exposure, days§ | |||
| Median (IQR) | 26 (21, 35) | 25 (21, 28) | |
| Fully vaccinated | 36 (27.9%) | 835 (39.4%) | 2.2 (1.3, 3.4) |
| Time interval between last vaccination and symptoms onset or last exposure, days§ | |||
| Median (IQR) | 49 (40, 54) | 48 (41, 56) | |
| Mode of detection | |||
| Passive surveillance | 14 (10.9%) | − | |
| Contact tracing | 80 (62.0%) | − | |
| Community screening | 35 (27.1%) | − | |