We're not at a stage yet when we can play favorites. It'll be a long time before we have the supply to prefer one over the other (except maybe in the US where there will be enough mRNA vaccines to go around).
A vaccinated person can have no symptoms of covid and still be spreading (This may or may not be true).
Folks are still studying how effective the vaccines are at preventing spread.
Aren't the efficacy numbers from the phase 3 trials based on giving periodic PCR tests to everyone that was participating in the trials? And not just based on people self-reporting symptoms?
It would be very surprising if there were a new kind of asymptomatic carrier that emerged only for people having taken certain vaccines in which they would never test positive on a PCR test but could still spread covid. The odds that this is how the vaccines work seems very small, relative to the number of times this argument that "we don't know yet" is getting repeated.
It just seems strange to me that so many people are hung up on pointing out that this small possibility is still a possibility. It seems more likely that this will drive more people to skip the vaccine, since they're being told they can't even go back to normal once vaccinated, than anything else.
There's some additional data which indicates Pfizer and Moderna are likely to limit transmission, but from my understanding it's not as ironclad as the symptomatic cases data.
For most trials, no. You have to look at each individual study, but most commonly, they only test after people show specific symptoms.