On Tuesday, the state Health Department estimated COVID breakthrough cases between January and August were 5.5%.
Now there's clear evidence infections among the fully vaccinated were increasing at a higher rate in the summer months.
The Allegheny County Health Department reports 23% the cases were breakthrough infections in August.
In July the number was 7% and in June 18%.
Health experts say the Delta variant is behind the increase and note the vaccine ensures nearly all people with breakthrough cases have mild symptoms.