Vaccination reduces the infection rate. Among vaccinated individuals who suffer breakthrough infection the time at peak viral load is significantly reduced.
CDC recommends testing of vaccinated people, since they can be infected and the vaccine suppresses symptoms, so they won't know to self-isolate, https://www.webmd.com/lung/news/20210729/cdc-reverses-guidan... (July 29, 2021)
> Even if they’re not showing symptoms, fully vaccinated people should “get tested 3-5 days after exposure to someone with suspected or confirmed COVID-19 and wear a mask in public indoor settings for 14 days after exposure or until they receive a negative test result,” ... “Our updated guidance recommends vaccinated people get tested upon exposure regardless of symptoms,” CDC Director Rochelle Walensky, MD, told The New York Times