“If you’re fully vaccinated, I would largely not worry about it,” said Dr. Ashish K. Jha, dean of the Brown University School of Public Health.
According to one recent study, the Pfizer-BioNTech vaccine was 88 percent effective at protecting against symptomatic disease caused by Delta, nearly matching its 93 percent effectiveness against the Alpha variant and 95 percent against the original version of the virus. But a single dose of the vaccine was just 33 percent effective against Delta, the study found.
“Fully immunized individuals should do well with this new phase of the epidemic,” said Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine. “However, the protection offered by a single dose appears low, and of course if you are not at all vaccinated, consider yourself at high risk.”
Delta is likely to infect “large numbers” of unvaccinated people, he said.
Will it cause a new surge in the United States?
It is unclear how much of a problem Delta will cause in the United States, where more than half of adults have been fully vaccinated. “I think we are not going to see another big, national surge in the United States because we have enough vaccination to prevent that,” Dr. Osterholm said.
Still, vaccination rates have been highly uneven, and are lower in certain states and demographic groups. Delta could fuel outbreaks in the South, where vaccinations lag, or among young people, who are less likely to be vaccinated than their elders.
“In places where there’s still a lot of susceptibility to the virus, it opens a window for cases to start going up again,” said Justin Lessler, an infectious disease epidemiologist at Johns Hopkins University. “But even in those states, and certainly nationally, we’re probably not getting back to the numbers we were seeing last winter.”