About 19% of recent documented COVID-19 cases in California are breakthroughs, and state data shows that those who have been fully vaccinated account for an increasing portion of positive tests.
In Contra Costa County, the seven-day average as of July 28 showed that 23% of the new cases were breakthroughs in fully vaccinated people. For Santa Clara County for about the same time period, the portion was 16%. Alameda County estimates 19% of new cases for the month of July were breakthroughs. And, doing the math, the portion for California was 19% as of July 31, up from 15% about two weeks earlier.