COVID cases increasing in unvaccinated as more breakthroughs pop up An epidemiologist with the Prince William Health District said in July, they estimate breakthroughs make up about 25% of positive COVID cases. Author: Jess Arnold Updated: 9:07 PM EDT July 25, 2021 PRINCE WILLIAM COUNTY, Va. — As COVID cases increase nationally and locally, researchers said they're starting to see more breakthrough cases. It's being seen in local communities and other parts of the United States. Prince William County epidemiologist with the local health district, Sean Morris, said they've seen a 100% to 150% increase in cases over the last several weeks. “We're seeing this divide of vaccinated and unvaccinated in the country. And I think that with a communicable disease, we always think of it as none of us safe until we all are safe," Morris said. "Variants occur due to the spread of disease. And the more spread there is, the more likely we are to get a new variant. That's what happened with the Delta variant.”