The Centers for Disease Control and Prevention has changed the way in which it is reporting breakthrough coronavirus cases, i.e. infections that occur in people who had previously been fully vaccinated. Starting with its latest release on July 26, the agency is no longer counting cases in which a breakthrough infection happened, but the patient wasn't hospitalized or died.
Either way, the data continues to show that vaccines have been highly effective at reducing hospitalizations and death. While breakthrough cases had been expected as no vaccine is 100 percent effective, their number represent an extremely small share of people fully vaccinated in the United States. As of July 26, around 163 million Americans had been fully vaccinated and the CDC's data states that among these people, 6,587 combined infections and hospitalizations and 1,263 combined infections and deaths occurred.
Data previously published had shown all breakthrough COVID-19 infections which as of April 30 had been 10,262 total cases, 995 of whom required hospitalization with 160 deaths recorded. The trends mirror those of Israel which has reported a handful of infections among its fully vaccinated population with a successful vaccine rollout resulting in both cases and hospitalizations collapsing.
The CDC release lists anyone who was admitted to hospital or died while also testing positive for COVID-19. This is why a small number of asymptomatic infections remains even after the data overhaul. The CDC furthermore estimates that around a quarter of hospitalizations as well as deaths in COVID-19 breakthrough cases were either asymptomatic or coincidental.