The Delta variant is the fastest, fittest and most formidable version of the coronavirus that causes COVID-19, and it is upending assumptions about the disease even as nations loosen restrictions and open their economies, according to virologists and epidemiologists.
The major worry about the Delta variant, first identified in India, is not that it makes people sicker, but that it spreads far more easily from person to person, increasing infections and hospitalizations among the unvaccinated.
Evidence is also mounting that it is capable of infecting fully vaccinated people at a greater rate than previous versions, and concerns have been raised that they may even spread the virus, these experts said.
In Singapore, where Delta is the most common variant, government officials reported on Friday that three quarters of its coronavirus cases occurred among vaccinated individuals, though none were severely ill.
Israeli health officials have said 60% of current hospitalized COVID cases are in vaccinated people. Most of them are age 60 or older and often have underlying health problems. In the United States, which has experienced more COVID-19 cases and deaths than any other country, the Delta variant represents about 83% of new infections. So far, unvaccinated people represent nearly 97% of severe cases.
‘‘There is always the illusion that there is a magic bullet that will solve all our problems. The coronavirus is teaching us a lesson," said Nadav Davidovitch, director of Ben Gurion University's school of public health in Israel.
A study in China found that people infected with the Delta variant carry 1,000 times more virus in their noses compared with the ancestral Wuhan strain first identified in that Chinese city in 2019.In the United States, the Delta variant has arrived as many Americans - vaccinated and not - have stopped wearing masks indoors.
"It's a double whammy," an expert said. "The last thing you want is to loosen restrictions when you're confronting the most formidable version of the virus yet.
"The development of highly effective vaccines may have led many people to believe that once vaccinated, COVID-19 posed little threat to them.
"When the vaccines were first developed, nobody was thinking that they were going to prevent infection," said Carlos del Rio, a professor of medicine and infectious disease epidemiology at Emory University in Atlanta. The aim was always to prevent severe disease and death, del Rio added. The vaccines were so effective, however, that there were signs the vaccines also prevented transmission against prior coronavirus variants. "We got spoiled," del Rio said.
