The CDC changes case identification policies for the vaccinated

As of May 1, 2021, CDC transitioned from monitoring all reported vaccine breakthrough cases to focus on identifying and investigating only hospitalized or fatal cases…

The following is the new standard for testing breakthrough cases:

For cases with a known RT-PCR cycle threshold (Ct) value, submit only specimens with Ct value ≤28 to CDC for sequencing. (Sequencing is not feasible with higher Ct values.)

Previously,  if a positive signal wasn’t seen after 37 to 40 cycles, the test was negative.  Each cycle increases the rate of a false positive.  So what was done here is that they dialing down the rate of false positive for these breakthrough cases.

Sources:

• 
  July 9, 2021. “COVID-19 Breakthrough Case Investigations and Reporting.” Centers for Disease Control and Prevention.
  https://www.cdc.gov/vaccines/covid-19/health-departments/breakthrough-cases.html.
  Centers for Disease Control and Prevention.
  To see the specifics of the new testing standard, you must click the + marks in the section just above the green bar with the text, “Resources to support submitting breakthrough case data to CDC.”
• 
  May 18, 2021. Kit Knightly. “How the CDC Is Manipulating Data to Prop-up ‘Vaccine Effectiveness.’” OffGuardian.
  https://off-guardian.org/2021/05/18/how-the-cdc-is-manipulating-data-to-prop-up-vaccine-effectiveness/.
  Blog.