When early field data showed that vaccinating people cuts transmission of the SARS-CoV-2 virus, researchers were cautiously optimistic. But they warned that many of those studies, although promising, took place before the fast-spreading Delta variant proliferated worldwide. Now, reports from various countries seem to confirm what scientists feared after the variant tore through India with alarming speed in April and May: Delta is more likely than other variants to spread through vaccinated people.
Data from COVID-19 tests in the United States, the United Kingdom and Singapore are showing that vaccinated people who become infected with Delta SARS-CoV-2 can carry as much virus in their nose as do unvaccinated people. This means that despite the protection offered by vaccines, a proportion of vaccinated people can pass on Delta, possibly aiding its rise.