The U.S. agency leading the fight against Covid-19 gave up a crucial surveillance tool tracking the effectiveness of vaccines just as a troublesome new variant of the virus was emerging.
While the Centers for Disease Control and Prevention stopped comprehensively tracking what are known as vaccine breakthrough cases in May, the consequences of that choice are only now beginning to show.
At the time, the agency had identified only 10,262 cases across the U.S. where a fully vaccinated person had tested positive for Covid. Most people who got infected after vaccination showed few symptoms, and appeared to be at low risk of infecting others.
But in the months since, the number of vaccine breakthrough cases has grown, as has the risk that they present. And while the CDC has stopped tracking such cases, many states have not. Bloomberg gathered data from 35 states and identified 111,748 vaccine breakthrough cases through the end of July, more than 10 times the CDC’s end-of-April tally.