US health officials on 30 July released details of an alarming new study which could totally muddle current thinking on how the coronavirus spreads in society.

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The latest research from the Centers for Disease Control and Prevention (CDC) shows that vaccinated people who got infected with COVID-19 or the so-called breakthrough infections carry about the same amount of the coronavirus as those who are unvaccinated. The study, published in CDC's flagship weekly report, is the basis for recent recommendations that vaccinated people wear masks indoors in places with high transmission rates - driven now by the delta variant. The report's authors suggest the CDC's new guidance should include masking in indoor public settings "regardless of vaccination status".

The study in question derives its insights from an outbreak in Provincetown, a popular tourist hotspot in Cape Cod, Massachusetts. After multiple large public events, 469 COVID-19 cases were identified among Massachusetts residents who had travelled to the town during July 3e17. Three fourths (74 per cent) of the cases were among fully vaccinated people. "Testing identified the Delta variant in 90 per cent of specimens from 133 patients," the report adds. "Cycle threshold values were similar among specimens from patients who were fully vaccinated and those who were not." The upshot: "Among persons with breakthrough infection, four (1.2 per cent) were hospitalised, and no deaths were reported." The release of this CDC report coincides with a Washington Post scoop of internal CDC documents that paint a grim picture of how the "war has changed" on COVID-19, after the delta variant seeped into America.