| Case Type | Definition* |
| Vaccine breakthrough | Fully vaccinated cases (i.e., ≥14 days have elapsed between the final vaccine dose and the specimen collection date) |
| Suspected reinfection | Repeat PCR-positive test ≥90 days after the initial PCR positive test |
| Unusual clinical presentations | Critical illness or death in a previously healthy child or young adult, unusual symptoms or laboratory findings, or other unusual cases |
| International travel | Completed travel ≤14 days prior to symptom onset (or specimen collection date if the individual is asymptomatic) |
| Zoonotic transmission | Suspected animal-to-human transmission |
| Outbreaks with a suspected variant of concern | Involve features noted above and/or high attack rate, unexpected proportion of cases with severe illness, or suspected unusual mechanism of transmission (e.g., longer-range airborne transmission, brief exposure, outdoor transmission, fomite, foodborne) |
*Also requires a Ct < 30 on RT-PCR results to be eligible for WGS.
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