Vaccinations give us some reassurance that we're safe from the novel coronavirus—but since no vaccine is 100 percent effective, you could still catch COVID after getting your shot(s), which is known as a breakthrough infection. However, the Centers for Disease Control and Prevention (CDC) has said that not only are these cases very rare—as in, there's only about a 0.01 percent chance—they're also more likely to be asymptomatic or mild, which means the vaccines are working as intended. In recent months, medical experts have said that not only does the vaccine prevent you from developing severe COVID, but vaccinated people who are infected are less likely to transmit the virus. Unfortunately, scientists just recently made a new discovery about breakthrough infections that may debunk that notion. According to a new study out of the University of Washington (UW) Medicine, vaccinated people who get COVID may be more likely to spread the virus than previously believed.
The May 25 study—which has not yet been peer-reviewed but was pre-printed on medRxiv—presented data on 20 fully vaccinated healthcare workers within the UW Medicine hospital system who ended up getting infected with COVID after being vaccinated. The breakthrough infections were recorded in people ages 26 to 65 between Feb. 23 and April 27.
Despite earlier research linking breakthrough infections with low viral loads—which suggests low transmission—study co-author Pavitra Roychoudhury, PhD, an acting instructor at UW Medicine, told Reuters that she and her team "found many samples in our breakthrough cohort with high viral load."
"Our work suggests that not all breakthrough infections are at low risk of initiating transmission," Roychoudhury explained.
According to the study, all 20 of the breakthrough infections were caused by variants of concerns. Of these cases, 40 percent were caused by the U.K. variant, B.1.1.7; another 40 percent were California variant B.1.429; 10 percent were the other California variant B.1.427; 5 percent were caused by South Africa variant, B.1.351; and another 5 percent were Brazil variant, P.1.
"Variants of concern (VOCs) are those strains that show evidence of increased transmissibility, more severe disease, reduced neutralization by antibodies elicited by past infection or vaccination, reduced efficacy of treatments, or failures in diagnostic detection," the UW Medicine researchers explained in their study. "Overall, variants of concern were proportionally over-represented in breakthrough cases."
In talking to Reuters, Roychoudhury cautioned: "These infections could lead to the continued spread of variants of concern, particularly in areas with low vaccination rates."
This is in-line with recent findings from the CDC. According to a new report from the agency, also published May 25, the CDC has detected more than 10,000 breakthrough infections in the U.S. out of nearly 101 million fully vaccinated individuals, as of April 30. After looking at the available sequencing data from these reported breakthrough cases, the agency found that 64 percent of fully vaccinated people who got COVID were infected by variants of concern. And the breakdown of cases was rather similar, too: 56 percent were B.1.1.7; 25 percent were B.1.429; 8 percent were B.1.427; another 8 percent were P.1; and 4 percent were B.1.351.
But more research still needs to be done to determine if the high viral loads of the breakthrough patients in the UW Medicine study definitively lead to increased COVID transmission.
"We also need to learn a little bit more, for those folks that do have those breakthrough infections, what their viral load looks like—how much virus they're actually carrying and shedding," Colleen Kelley, MD, associate professor of infectious diseases at Emory University School of Medicine and a principal investigator for the Moderna and Novavax phase III clinical trials, recently said on the Track the Vax podcast in mid-May. "The viral load certainly is going to correlate with transmissibility. And so those are some additional data that we're waiting on." This latest study could very well change what Kelley and many others have long believed to be true about breakthrough infections not being as contagious.