Seasonality is just one of many factors that affect the spread of COVID. Blindly comparing the situation now with one year ago really doesn't make any sense.
Vaccine efficacy against infection has been measured in a lot of studies, for example [1, 2, 3]. It has also been shown that being vaccinated reduces viral loads after infection, even with the delta variant [4, 5]. There are also a few studies on household transmission [5, 6] that show that transmission between vaccinated individuals is significantly less likely.