The federal Centers for Disease Control and Prevention reported this week that 10,262 fully vaccinated people in 46 states and territories tested positive for COVID-19 between Jan. 1 and April 30.
While the number of breakthrough cases is not trivial, it represents a miniscule proportion (.01%) of the 101 million people who were fully vaccinated on April 30.
Breakthrough cases are expected, the CDC said, because no vaccine is 100% effective. But there is evidence that COVID-19 vaccines make the illness less severe for those who do get sick.
Of the total number of breakthrough cases, 995 (10%) people were hospitalized and 160 (2%) died. Among those who were hospitalized, 29% were asymptomatic or were hospitalized for reasons that had nothing to do with COVID-19. Of the fatalities, 18% died of unrelated causes.
The CDC also announced that it had stopped collecting data on all breakthrough COVID-19 cases as of May 1, in part because the data was unreliable. The number of cases is vastly underreported, the agency explained, because vaccinated people with no symptoms or only mild symptoms of COVID-19 are unlikely to get tested.
The CDC announced it will focus on identifying and investigating only hospitalizations and fatal cases due to any cause. “This shift will help maximize the quality of the data collected on cases of greatest clinical and public health importance,” the agency said.
Some state, local and territorial health departments may continue to report all breakthrough cases, the CDC said.
In its investigations of breakthrough cases, the CDC plans to identify trends in patient characteristics, such as age and underlying health conditions, as well as the brand of vaccine they received and whether a COVID-19 variant was involved.
Under the new reporting scheme, the CDC said that 1,811 vaccinated people with breakthrough COVID-19 cases were hospitalized and another 353 died between May 1 and May 17.
Of those hospitalized, 25% were treated for unrelated conditions. Of the fatalities, 18% were for reasons unrelated to COVID-19.
Through April 30, 63% of breakthrough cases occurred in women, and the median patient age was 58 years. The median age of people who died was 82.
As of May 17, more than 123 million Americans were fully vaccinated. On May 27, the number was nearly 132 million. As more people are vaccinated, more breakthrough cases—including hospitalizations and deaths—can be expected, health officials say.