Masks are somewhere between 10% effective for cheap disposable masks up to 50%, or more, effective for N95 masks. Having said that why not wear the damn mask and get every advantage possible. Something else to consider, even after you are fully vaccinated all that means is your body will fight off the virus. That doesn't mean you can't be spewing virus as you body fights it off while preventing infection. Even after vaccination we should consider continuing wearing the mask for the those not yet vaccinated.