I don't think either of those sources justifies "does little to prevent spread." The language used in them is considerably more hedged, eg:
"But growing evidence suggests that, with the Delta variant, fully vaccinated people can still transmit the virus."
And this:
"Unfortunately, the vaccine’s beneficial effect on Delta transmission waned to almost negligible levels over time. In people infected 2 weeks after receiving the vaccine developed by the University of Oxford and AstraZeneca, both in the UK, the chance that an unvaccinated close contact would test positive was 57%, but 3 months later, that chance rose to 67%. The latter figure is on par with the likelihood that an unvaccinated person will spread the virus."
Is also not super relevant— what most people want to know is not whether a breakthrough infection is capable of spreading it, but whether you're more likely to get a breakthrough infection. I think most vaccinated people (which is most people in rich countries now) care much more about the unvaccinated -> vaccinated transmission and the vaccinated -> vaccinated transmission than they do about vaccinated -> unvaccinated.
"But growing evidence suggests that, with the Delta variant, fully vaccinated people can still transmit the virus."
And this:
"Unfortunately, the vaccine’s beneficial effect on Delta transmission waned to almost negligible levels over time. In people infected 2 weeks after receiving the vaccine developed by the University of Oxford and AstraZeneca, both in the UK, the chance that an unvaccinated close contact would test positive was 57%, but 3 months later, that chance rose to 67%. The latter figure is on par with the likelihood that an unvaccinated person will spread the virus."
Is also not super relevant— what most people want to know is not whether a breakthrough infection is capable of spreading it, but whether you're more likely to get a breakthrough infection. I think most vaccinated people (which is most people in rich countries now) care much more about the unvaccinated -> vaccinated transmission and the vaccinated -> vaccinated transmission than they do about vaccinated -> unvaccinated.