The UK paper on Delta seemed to suggest that wasn’t true even for the unvaccinated-never infected as well. Google the Lancet article. Viral loads were similars, infection risk wasn’t that much lower for vaccinated. I think recovery was quicker by a day, maybe.
Research from Australia suggests otherwise. 20x.
Also, got a journal article to reference? The UK data is pretty good for Delta. That is a quote by the health authority with no references given.
https://www.thelancet.com/journals/laninf/article/PIIS1473-3...
Vaccination reduces the risk of delta variant infection and accelerates viral clearance. Nonetheless, 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.
Another ignorant author who does not know that natural immunity exists outside of vaccines... I.e those who recovered from COVID.