here_we_go_again
Quite. More than that, it shows that
breakthroughs shed virus! This is not surprising. By definition, this is the subset of vaccinated people who became sick. This is NOT a comparison of vaccinated and unvaccinated people. This is a comparison of Delta variant shedding in sick people vs shedding in patients with "old strains detected between March-April 2020". This high level of virus shedding in sick people with the Delta variant underlines the importance of vaccination.
This is the conclusion that the authors come to. I think they are best placed to understand the implications of their work:
Breakthrough Delta variant infections are associated with high viral loads, prolonged PCR positivity, and low levels of vaccine-induced neutralizing antibodies, explaining the transmission between the vaccinated people. Physical distancing measures remain critical to reduce SARS-CoV-2 Delta variant transmission.