January 28, 2023

The super-contagious Delta variant of the coronavirus is now responsible for about one in five Covid-19 cases in the United States, and its prevalence has doubled in the past two weeks, health officials said on Tuesday.

Delta was first identified in India and is one of several “Concerning Variants” named by the Centers for Disease Control and Prevention and the World Health Organization. It quickly spread to India and the UK.

Its appearance in the United States is not surprising. And with vaccinations rising and Covid-19 case numbers falling, it’s unclear how much of a problem Delta will cause here. Still, its rapid surge has raised concerns that it could jeopardize the nation’s progress in fighting the pandemic.

“The Delta variant is currently the greatest threat in the US to our attempt to eliminate Covid-19,” said Dr. Anthony S. Fauci, the country’s foremost infectious disease expert, at the briefing. The good news is that the vaccines approved in the USA work against the variant. “We have the tools,” he says. “So let’s use them and crush the outbreak.”

Here you will find answers to some frequently asked questions about the Delta variant.

Delta, formerly known as B.1.617.2, is believed to be the most transmissible variant to date and is spreading more easily than both the original strain of the virus and the alpha variant first identified in the UK. Public health officials said Delta could be 50 percent more contagious than Alpha, although exact estimates of its infectivity vary.

Other evidence suggests that the variant may be able to partially bypass the antibodies produced by the body after a coronavirus infection or vaccination. And the variant can also make certain monoclonal antibody treatments less effective, the CDC notes.

Delta can also cause more serious illnesses. For example, a recent Scottish study found that people infected with the Delta variant were about twice as likely to be hospitalized as people infected with alpha. But uncertainties remain, scientists said.

“The article on serious illnesses is the one question I think that hasn’t really been answered,” said Dr. Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota.

Delta has been reported in 80 countries. It is the most common variant today in India and the UK, where it accounts for more than 90 percent of cases.

Delta was first identified in the United States in March. Although Alpha remains the most widely used variant here, Delta has spread quickly. At the beginning of April, Delta only made 0.1 percent of cases in the United States, according to the CDC. By early May, the variant accounted for 1.3 percent of cases, and by early June that number had risen to 9.5 percent. A few days ago, the estimate was 20.6 percent, said Dr. Fauci at the meeting.

The delta variant is unlikely to pose a huge risk for fully vaccinated people, experts said.

“If you are fully vaccinated I wouldn’t worry about that,” said Dr. Ashish K. Jha, Dean of Brown University School of Public Health.

According to a recent study, the Pfizer BioNTech vaccine protected 88 percent against symptomatic illnesses caused by Delta and was nearly 93 percent effective against the alpha variant. But a single dose of the vaccine was only 33 percent effective against Delta, the study found.

“Fully immunized people should be able to cope 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 that a single dose offers seems to be poor and if you are not vaccinated at all you naturally consider yourself at high risk.”

Understand India’s Covid Crisis

Delta will likely infect “large numbers” of unvaccinated people, he said.

The pandemic is decreasing in the United States, with cases, hospital admissions and deaths falling. The seven-day case average, around 10,350 per day, is the lowest since March 2020, said Dr. Rochelle Walensky, director of the CDC, at the briefing on Tuesday. “These numbers show the extraordinary progress we’ve made against a formidable opponent,” she said.

So while Delta may represent an increasing percentage of cases, it is not yet clear whether this will increase the total number of cases.

“I don’t think we’re going to see another big, national surge in the United States because we have enough vaccinations to prevent this from happening,” said Dr. Osterholm.

Still, vaccination rates were very uneven and lower in certain states and populations. Delta could fuel outbreaks in the south, where vaccinations are delayed, or in young people who are less likely to be vaccinated than their elders.

“In places where the virus is still very vulnerable, this opens a window for the resumption of cases,” said Justin Lessler, an infectious disease epidemiologist at Johns Hopkins University. “But even in these states, and certainly nationally, we are unlikely to go back to the numbers we saw last winter.”

Still, he said, it could make our way out of the pandemic longer. “The slack continues,” he said.

To be vaccinated. If you’ve already been vaccinated, encourage family, friends, and neighbors to get vaccinated. Vaccination is likely to slow the spread of all variants and reduce the likelihood that new, even more dangerous, variants will emerge.

“I encourage people who have been vaccinated to trust vaccines, but be aware that there will continue to be new varieties of transmission,” said Saskia Popescu, infectious disease epidemiologist at George Mason University. “So it’s really about ensuring local, national and global vaccinations.”