US sees breakthrough infections with arrival of Delta variant

NEW YORK • Since Americans first began rolling up their sleeves for Covid-19 vaccines, health officials have said those who are inoculated are very unlikely to become infected with the virus, or to suffer serious illness or death. But preliminary data from seven states in the United States hints that the arrival of the Delta variant last month may have altered the calculus.

Breakthrough infections in vaccinated people accounted for at least one in five newly diagnosed cases in six of these states and higher percentages of total hospitalisations and deaths than had been previously observed in all of them, according to figures gathered by The New York Times.

The absolute numbers remain very low, however, and there is little doubt that the vaccines remain powerfully protective. This continues to be "a pandemic of the unvaccinated", as federal health officials have said. Still, the rise indicates a change in how vaccinated Americans might regard their risks.

The seven states - California, Colorado, Massachusetts, Oregon, Utah, Vermont and Virginia - were examined as they are keeping the most detailed data. It is not certain that the trends in these states hold throughout the country.

Scientists have always expected that as the population of vaccinated people grows, they will be represented more frequently in tallies of the severely ill and dead.

"We don't want to dilute the message that the vaccine is tremendously successful and protective, more so than we ever hoped initially," said Dr Scott Dryden-Peterson, an epidemiologist at Brigham and Women's Hospital in Boston. "The fact that we're seeing breakthrough cases and breakthrough hospitalisations and deaths doesn't diminish that it still saves many people's lives."

The states' data do affirm that vaccinated people are far less likely to become severely ill or to die from Covid-19. In California, for example, the 1,615 hospitalisations of people with breakthrough infections as at Aug 8 represent just 0.007 per cent of nearly 22 million fully vaccinated residents, and breakthrough deaths are an even smaller percentage.

Emory University biostatistician Natalie Dean said: "There's just a lot more virus circulating, and there's something uniquely infectious about the variant."

A vast majority of vaccinated people who are hospitalised for Covid-19 are likely to be older adults or those who have weakened immune systems for other reasons. Data from the Centres for Disease Control and Prevention shows that 74 per cent of breakthrough cases are among adults aged 65 or older. Breakthrough infections are also likely to be most severe among older adults or those who have conditions such as obesity or diabetes.

NYTIMES