Characteristics of study participants
Of the positive cases, 239 (57.7%) were asymptomatic patients, and the
remaining 42.3% were symptomatic. Among the symptomatic patients,
symptoms reportedly included fever (n = 76, 43.4%), cough (n = 66,
37.7%), pharyngitis (n = 45, 25.7%), rhinitis (n = 21, 12%), fatigue
(n = 16, 9.1%), diarrhea (n = 2, 1.1%) and chest discomfort (n = 1,
0.6%) (Table 1). Among the 414 cases and 828 controls, 255 (61.6%) and
394 (47.6%) individuals were female, respectively. The mean “time
since the last dose of vaccination” was 6.8 months (3.0–8.0 months)
for cases and 3.8 months (2.9–7.5 months) for controls. There was a
significant difference between the two groups in terms of “gender” and
“time since the last dose of vaccination” (P < 0.001,P = 0.01). The median age was 38 years (18–55 years) in the case
group, and 40 years (25–56 years) in the control group, and no
statistical difference was observed (P = 0.353) ( Table
2).