About 5,800 fully vaccinated Americans – of the 66 million who got the shots – still became infected with COVID-19, according to data from Centers for Disease Control and Prevention reported Thursday.
The infections, so-called breakthrough cases – or positive test results that occur at least two weeks after a person receives their last dose of coronavirus vaccine – represent about 0.008 percent of Americans who are fully vaccinated, the Wall Street Journal reported.
The federal agency found that 29 percent of breakthrough infections were asymptomatic, while 7 percent resulted in hospitalization. To date, 74 people have died of breakthrough infections – but it is not clear which vaccine they received, whether the patients were from high-risk groups, or if there were other conditions that contributed to the deaths.
More than 40 percent of the breakthrough cases, which come from just 40 states, occurred in people over the age of 60, and 65 percent of those infected were women, the CDC told the outlet.
The CDC is expected to publish findings on the breakthrough infections next week, the outlet reported.
On Thursday, CDC director Dr. Rochelle Walensky on Capitol Hill on what could be causing the breakthrough infections, saying the agency is “watching things closely.”
“Some of these breakthroughs are, of course, the failure of an immune response in the host, and for some of them, we fear they may be related to a variant that is circulating, so we’re looking at both,” Walensky said.
Health officials have said breakthrough infections are expected because none of the vaccines currently approved for distribution are 100 percent effective.
“You will always see some breakthrough infections regardless of the effectiveness of your vaccine,” said Dr. Anthony Fauci at the outlet.
“Before people get excited about the quantitative rate of infections, they need to understand what the denominator is, and we’ll see breakthroughs in numbers well within the 90 percent, 95 percent, 97 percent vaccine effectiveness rates.”
There are a number of reasons people can become infected after being fully vaccinated, David Hirschwerk, an infectious diseases physician for Northwell Health System, told the WSJ.
People who are older or those with compromised immune systems may not be able to launch a robust immune response to the vaccine and build enough antibodies to ward off infections, the doctor explained.
In other situations, new variants, some of which have proven to be more transferable, may circumvent the vaccine’s protection. And sometimes a patient could just be exposed to a particularly heavy viral load during a superspreader event, for example, the outlet said.
“The experience so far is that the vaccine remains very effective and those who have had breakthrough infections have had very mild and manageable illnesses,” Hirschwerk, who treated a patient with a breakthrough infection, told WSJ.
“This is really what we see every season with the flu vaccine.”
The CDC plans to perform genomic sequencing on respiratory samples taken from patients with breakthrough infections to gain a better understanding of the role variants play and how they hold up against the vaccines.
Additional reporting by Jackie Salo