The Centers for Disease Control and Prevention will report only those breakthrough cases resulting in hospitalization or death. The agency also lowered the testing threshold, but only for the fully vaccinated (ie PCR reduced to 28 cycles results in fewer false positives).

https://childrenshealthdefense.org/defender/cdc-changes-rules-counting-breakthrough-cases/?utm_source=salsa&eType=EmailBlastContent&eId=4d3a5a92-4213-46f8-a5f5-c14b564d90cf