With the emergence of the delta variant driving new breakthrough infections, some are wondering what impact the strain may have on reinfection rates. In the fall, the Centers for Disease Control and Prevention (CDC) advised that some cases of reinfection are expected, but "remain rare."
However, that guidance published by the agency was last updated in Oct. 2020, which was prior to the vaccination rollout and before the discovery of the delta variant. The frequency regarding reinfection is not well known, one expert warned, and is difficult to track.
"It’s important to emphasize how difficult it is to come up with good quality evidence on reinfection because it requires documentation by a second PCR test and ideally sequencing of the virus," Dr. Ricardo Franco, MD, Infectious Disease Society of America (IDSA) member and associate professor of medicine at the University of Alabama at Birmingham (UAB), said Tuesday.
Franco also noted the difficulty in determining whether it’s reinfection or a reemergence of the virus that the patient was harboring.
Another expert said low test rates in the U.S. are hampering efforts to get a clear picture of breakthrough cases and asymptomatic spread. Emerging data suggest that asymptomatic vaccinated individuals are capable of transmitting the virus to others, but with mass testing sites closing and a decrease in accessibility outside of working hours, it’s likely many cases are going undetected.
Dr. Ezekiel Emanuel, MD, PhD, vice provost for global initiatives at the University of Pennsylvania and co-director of the health transformation institute, called the asymptomatic breakthrough cases "the worrisome group."
He cautioned that without proper surveillance it would be difficult to monitor for and detect the next variant that potentially evolves.
"If you’re missing breakthrough infections – a lot of them – you may be missing some evolution here that would be very important for us to follow," he said.
Franco also noted that there are a lot of unknowns regarding the delta variant's impact on natural immunity. He said there is "some indication" that natural immunity offers a lower quality of protection than immunity achieved through vaccination, but it’s not clear how much lower.
The CDC said it is "actively working" to learn more on reinfections.