Objective To describe clinical and epidemiological characteristics of cases infected with novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant diagnosed during February – May, 2023 in a district of Beijing city for effective containment of coronavirus disease 2019 (COVID-19) epidemic.
Methods The surveyed cases were 110 laboratory-confirmed novel SARS-CoV-2 variant infections diagnosed in sampling inspection and surveillance at customs departments and medical institutions and reported to health agency of Chaoyang district of Beijing city during February – May, 2023. The collected data were analyzed with descriptive statistics. The novel SARS-CoV-2 variant refers to the SARS-CoV-2 strains not detected previously in the district (except for BA.5.2/ BF.7 and their sub-variants).
Results The 110 cases were consisted of 64 males and 46 females, with a median age of 32 years; compared to those in the local cases, significantly higher median age and proportions of COVID19 vaccination and secondary attack were observed in the 72 (65.45% of all the cases) imported cases (P < 0.05 for all). Among all the cases, 100 (90.91%) were identified as having infections of SARS-CoV-2 XBB variant and subvariants based on whole-genome sequencing analysis. The number of symptomatic cases was 100 (90.91% of all cases) and main clinic symptoms were fever (66.00% in proportion), sore throat (53.00%), and cough (52.00%); and 35.00% of the symptomatic cases could be diagnosed as influenza-like illness. Significantly more symptomatic cases were observed in initial infections than in the reinfections (P = 0.004). For all the cases, The duration of negative seroconversion of SARS-CoV-2 nucleic acid or antigen was 5.92 ± 2.95 days and the disease course of was 5.00 (percentile 25∶4.00, percentile 75∶8.75) days. Compared to the cases with initial infection, the cases with reinfection had significant shorter duration (5.08 ± 2.60 days vs. 6.49 ± 3.06 days) of negative seroconversion of SARS-CoV-2 nucleic acid or antigen (P = 0.026). Prevalence of clinical symptoms and the duration of negative seroconversion of SARS-CoV-2 nucleic acid or antigen were not significantly different between the cases with SARS-CoV-2 XBB variant infection and the cases with non-XBB infection (P > 0.05). The epidemiological survey among the 110 cases identified totally 252 intimately close contacts and the secondary attack rate in the close contacts was 12.70%; the secondary attack rate was higher in the contacts of non-XBB variant infections than in the contacts of XBB variant infections.
Conclusion During February to May 2023 in a district of Beijing, the majority of reported novel SARS-CoV-2 variant cases were imported cases; most of the local cases were initial infections; the proportion of symptomatic cases was higher in initial infections than that in the reinfections but the initial infections had a longer duration of negative seroconversion of SARS-CoV-2 nucleic acid or antigen than the reinfections; the secondary attack rate was higher in the contacts of non-XBB variant infections than in the contacts of XBB variant infections.
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