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SARS-CoV-2 B.1.617.2 (Delta) Variant COVID-19 Outbreak Associated with a Gymnastics Facility – Oklahoma, April-May 2021

Our take —

This study described an outbreak of the SARS-CoV-2 Delta variant that was associated with an indoor gymnastics facility in Oklahoma in the late spring of 2021. This cluster included 47 cases among 194 exposed individuals; two patients were hospitalized, and there were no fatalities. Vaccine coverage among those who were exposed was low (in part, due to vaccine eligibility guidelines), and a small number of vaccine breakthrough infections were observed. This study demonstrates that the Delta variant is highly transmissible in indoor sports settings and within households. Current evidence indicates that vaccines remain effective against the Delta variant. Multicomponent prevention strategies (i.e., masking, social distancing, quarantine) remain important for limiting transmission, especially in high-risk settings with low rates of vaccination and high prevalence of the Delta variant.

Study design


Study population and setting

This study described an outbreak of SARS-CoV-2 Delta variant cases associated with an Oklahoma gymnastics facility between April 15 and May 3, 2021. This cluster of cases was initially identified by the Oklahoma Department of Health, Acute Disease Service through routine surveillance and sequencing. Contact tracing was performed to identify potential exposures and linked cases. Team and staff rosters from the Oklahoma facility and participant lists from two regional meets that took place during this time period were compared to Oklahoma’s COVID-19 surveillance data to identify additional linked cases. State immunization records were used to confirm vaccination status of all cases and contacts. Available specimens were sequenced to confirm variant status.

Summary of Main Findings

This cluster of SARS-CoV-2 Delta variant infections included 47 cases (median patient age, 14 years; range, 5-58 years) among 194 identified exposed persons between April 15 and May 3, 2021 (overall attack rate: 24%). Cases included 23 gymnasts (from 10 of 16 cohorts), 3 staff members, and 21 household contacts (from 7 of 26 interviewed households). Two adults were hospitalized, one of which required treatment in the ICU; neither were vaccinated. At the time, 74 (38%) of the exposed persons were eligible for vaccination based on local guidelines, but only 17 (9%) were fully vaccinated. Four vaccine breakthrough cases were identified in this cluster (Moderna and Pfizer); three additional cases were identified in individuals who had received only one vaccine dose. Despite the participation of 4 infected gymnasts in two regional meets during the contagious period, there was no evidence of secondary spread at either event. Of the confirmed cases, 21 were attributed to the Delta variant based on sequencing results, while 26 were attributed based on direct epidemiologic linkage to another variant cases. Environmental risk factors identified during household interviews included quarantine nonadherence, low rates of testing, delayed infection recognition due to mild symptoms, lack of mask wearing, poor ventilation, overlapping cohorts, and inadequate cleaning.

Study Strengths

This study describes a SARS-CoV-2 Delta variant outbreak associated with an indoor gymnastics facility. Cases were identified through robust contact tracing efforts, and results were contextualized based on known vaccination status.


Only cases reported to the state surveillance system were included in counts; additional exposed persons with mild or asymptomatic infection may have not been tested for SARS-CoV-2, leading to underestimates of case counts. Voluntary patient interviews could have led to underreporting of contacts and infection related details. Delays in updates to the state vaccine database could have resulted in underestimation of vaccination rates. Less than half of outbreak cases had samples available for sequencing to confirm variant status. Vaccine effectiveness could not be determined because not all exposed individuals could be interviewed and because state vaccination data was incomplete.

Value added

This is a thorough description of a cluster of SARS-CoV-2 Delta variant infections that was associated with a gymnastics facility in Oklahoma in the late spring of 2021.

This review was posted on: 30 July 2021