One reason for this may be that vaccinated people carry less infectious virus particles, as (not-yet-peer-reviewed) research from the Netherlands has recently illustrated. Although it’s widely assumed that virus particles carried by the vaccinated and unvaccinated are the same, basic principles of immunology actually predict otherwise, Kedl told me. Virus particles expelled by a vaccinated person are thought to be coated in antibodies—some of which are produced in the nose and mouth and are considered part of “mucosal” immunity—so “we can expect less of a downstream transmission,” he said.
Other researchers have come to similar conclusions. “The data are very clear that vaccinated individuals are less likely to spread the virus to others than unvaccinated individuals,” Christopher Byron Brooke, an assistant professor at the University of Illinois at Urbana-Champaign, told me in an email. A recent paper Brooke co-wrote showed that vaccinated people shed less virus, stop shedding virus sooner than the unvaccinated, and shed particles that are less infectious—supporting the notion that they’re less likely to transmit disease. One study from the Netherlands found a 63 percent reduction in household transmission among the vaccinated. That’s a testament to our vaccines: Homes are a “setting where the deck is heavily stacked towards transmission since members of a household are in extremely close contact for long stretches of time,” Brooke said. (However, another recent study didn’t find a statistically significant difference in household transmission between vaccinated and unvaccinated people.) Ultimately, Brooke said, you can certainly say the transmission risk for vaccinated people is lower, “but I don’t really know how you define ‘low.’”
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