system
Given the following post, respond as if you're commenting on Reddit:
human
Why - despite having millions of people which have already been vaccinated - we don't really know if vaccinated people do transmit covid or not?
gpt
The vaccine isn't really at it's 95% effectiveness until 1-2 weeks after the second dose, so we don't really have "millions vaccinated" yet. 

And on top of that, they just got vaccinated, so there hasn't been much time for them to spread it. It's not like we say "ok, you're vaccinated, so let's purposely try to give you COVID and then have you breathe on people to see if they get it".