The U.S. Centers for Disease Control and Prevention (CDC) in May 2021 stopped tracking all breakthrough cases of COVID-19, or those that occur in vaccinated people, and has since only tracked breakthrough cases that lead to hospitalization and death. While the agency has published several studies in the past year as part of an effort to better understand the effectiveness of vaccines, some critics say not having a national tally of breakthrough cases is limiting that effort. “Lack of complete and representative data on breakthrough cases means that it is not possible to estimate the risk of breakthrough cases among vaccinated people,” said Dr. Harvey Risch, professor of epidemiology at the Yale School of Public Health, in an email to The Epoch Times. “[Without the data on breakthroughs] the benefit of the vaccines for risk of infection cannot be estimated accurately during the Delta and Omicron waves,” Risch said. Public health …