A school cluster outbreak of COVID-19 caused by SARS-CoV-2 Omicron variant

  Objective  To analyze a cluster outbreak of coronavirus disease 2019 (COVID-19) caused by the Omicron variant of severe acute respiratory syndrome coronavirus virus 2 (SARS-CoV-2) in a boarding school for providing a reference to COVID-19 epidemic prevention and control.

  Methods  From China Information System for Disease Control and Prevention, we extracted the information on all COVID-19 cases laboratory-confirmed during January 8 – 19, 2022 among the students and teachers in a boarding school at a county in Henan province. Incidence rate (proportion) and histogram were used to describe epidemiological characteristics of the outbreaks. Basic reproduction number (R₀) and time-varying reproduction number (Rt) were calculated with R software.

  Results  Totally 283 COVID-19 cases infected with SARS-CoV-2 Omicron BA.1 variant were diagnosed during the 12-day period and the attack rate was 6.8% for the 4 124 students and teachers of the school. The cases occurred in 23 classes (all for senior high school students and only one for junior high school students) and the class-specific attack rate ranged 1.6% – 76.8%. For the 269 student cases at a mean age of 17.0 ± 0.9 years, the male to female ratio was 1 : 1.09; while the mean age was 24.0 (25th percentile = 23.0, 75th percentile = 30.0) years for the 14 teacher cases. The estimated R₀ was 5.46 (95% confidence interval: 3.11, 8.77); the estimated Rt increased first and then declined. Obvious symptoms were observed among 18.4% (52) of all cases and major clinical manifestations included fever, sore throat and cough, which occurred in 69.2%, 30.8% and 19.2% of the 52 sufferers. The confirmed cases were clinically classified as common or mild type patients.

  Conclusion  The Omicron variant of SARS-CoV-2 identified among the cases of the school cluster outbreak of COVID-19 was highly contagious but induced relatively mild clinical symptoms. Follow up studies need to be conducted among the cases of the epidemic outbreak to assess long-term adverse effects of the viral infection in the infected people.