Superspreading event of COVID-19 in adolescents: is there a difference between the vaccinated and the unvaccinated?

Objective: The aim of this study is to estimate the incidence of COVID-19 in a vaccinated and an unvaccinated group of adolescents and describe their symptoms.   Methods: In May 2021 a private indoor event for high school adolescents took place resulting in a superspreading event. As part of the study, an anonymous questionnaire was sent to all adolescents invited to the event and details about symptoms, previous COVID-19 infection, vaccination status and behaviour during the event was assessed. Two groups were formed, one of vaccinated individuals and the other of unvaccinated individuals. A sample from a fully vaccinated symptomatic individual was sequenced. General characteristics for the studied groups are described using categorical and continuous data. The incidence of COVID-19 in each group was estimated by taking the total number of COVID-19 positive cases (numerator) divided by the total number of individuals (denominator) multiplied by 100.   Results: A total of 41 out of the 164 adolescents (incidence 25%, 95%CI 18.6- 32.4) that attended the private indoor event developed COVID-19. A sample was sequenced from one of the symptomatic and fully vaccinated individuals with BNT162b2 (Pfizer-BioNTech vaccine) finding SARS-CoV-2 Delta (B.1.617.2) variant of concern. The incidence of COVID-19 in the unvaccinated was 35.1% (95%CI 25.5-45.6), and in the vaccinated 11.4% (95%CI 5.1-21.3). There were more unvaccinated than vaccinated teenagers that developed COVID-19