A new study from the Netherlands concluded that when rare breakthrough COVID-19 infections occur in vaccinated individuals, the viral loads are comparable to those in unvaccinated, infected people. But there's simultaneously less infectious viral particle shedding, which in other words suggests that vaccinated people are probably still less likely to transmit the virus, though further study is necessary.
The non-peer reviewed findings are based on an analysis of 161 breakthrough infections — the majority of which were caused by the Delta variant — among a population of 24,706 vaccinated health-care workers. They seem to line up with some other evidence that indicate a reduced transmission risk among the vaccinated who contract the virus.
While that appears to be good news, the Dutch study does leave some room for concern, since 68 percent of the samples were still found likely to be infectious, a number that the University of Pittsburgh's Walid Gellad thinks is too high for comfort.