Background Pre-Delta, vaccination reduced transmission of SARS-CoV-2 from individuals infected despite vaccination, potentially via reducing viral loads. While vaccination still lowers the risk of infection, similar viral loads in vaccinated and unvaccinated individuals infected with Delta...
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"The single measured Ct value only approximates viral load at the time of transmission, as viral loads are dynamic over time.
22 Hence, observed viral loads may not be representative of viral loads at transmission, however, the strong relationship between measured Ct values and risk of onward transmission argues against this
15 (replicated here,
Figure 4B). Therefore, it is possible vaccination acts by facilitating faster clearance of viable infectious virions,
17,
18 but leaving damaged ineffective virions behind that still contain PCR-detectable RNA. This may mean antigen assays have advantages in predicting the risk of onward transmission in those vaccinated, but this needs further study."
Read that please. It's preliminary and not yet peer-reviewed, but the data is there.