"Asked to explain the change, a C.D.C. spokeswoman said that no vaccine was 100 percent effective, but that the number of Covid-19 cases in fully vaccinated people was small and that no significant demographic trends had been identified.
"...“We have to prioritize what we’re doing, and the priority is to understand the cases associated with severe disease,” Dr. Kathryn Edwards, a professor of pediatrics at Vanderbilt University School of Medicine who studies vaccine safety and effectiveness, said of the new C.D.C. policy.Some private health care systems are also studying vaccination failures among employees that will yield useful data, she said, though such studies are not necessarily reflective of broader trends.
“It’s such a rare phenomenon, and it doesn’t change the trajectory of the pandemic,” said Dr. Amesh A. Adalja, a senior scholar at Johns Hopkins Center for Health Security. As long as the disease is not causing people to require hospitalization, “there’s marginal value to tracking it,” he said, adding, “It doesn’t have the ability to crush the hospital system anymore.”
https://www.nytimes.com/2021/05/25/health/cdc-coronavirus-infections-vaccine.html
