QUOTE: "fully vaccinated individuals with breakthrough infections have peak viral load similar to unvaccinated cases and can efficiently transmit infection in household settings, including to fully vaccinated contacts"
Reference: https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(21)00648-4/fulltext
Community transmission and viral load kinetics of the SARS-CoV-2 delta (B.1.617.2) variant in vaccinated and unvaccinated individuals in the UK: a prospective, longitudinal, cohort study
"While the primary aim of vaccination is to protect individuals against severe COVID-19 disease and its consequences, the extent to which vaccines reduce onward transmission of SARS-CoV-2 is key to containing the pandemic. This outcome depends on the ability of vaccines to protect against infection and the extent to which vaccination reduces the infectiousness of breakthrough infections."
SOURCE: The Lancet Infectious Diseases Journal -- Open Access