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Here’s what you need to know about the COVID-19 delta variant

With a new coronavirus variant on the rise, officials are urging people to get their coronavirus shots.Lane Turner/Globe Staff

A new villain has taken the stage in the battle against the coronavirus: the delta variant. Here, compiled from Globe wire service and major media reports, is what you need to know about this new player causing concern even as the US pandemic is waning.

What is the delta variant?

Variants are mutations of the coronavirus. Scientists say viruses constantly mutate naturally as they replicate and circulate in their hosts. Sometimes these mutants disappear; other times they persist. This variant, technically known as B.1.617.2, is gaining ground around the world after being first detected in India, where it is believed to have contributed to that country’s recent terrifying surge.


Why “delta”? The World Health Organization has introduced a new Greek alphabet naming convention for variants to simplify things and reduce the stigma for countries where variants emerge.

Why are people getting concerned?

The variant has quickly spread into the United Kingdom, where it appears to be fueling an uptick in coronavirus cases despite the UK’s successful response to the pandemic earlier this year. Dr. Anthony Fauci, President Biden’s chief medical adviser for the pandemic, said Tuesday that the delta variant is “rapidly emerging as the dominant variant” in Great Britain, accounting for more than 60 percent of new cases.

“It’s essentially taking over” there, Fauci said at a White House coronavirus response team briefing. “We cannot let that happen in the United States.”

The delta variant has also been detected in 60 other countries, he said. And here in the United States, it is already accounting for more than 6 percent of new cases.

Why is the delta variant a problem?

The delta variant is believed to be 60 percent more transmissible than the B.1.1.7 variant (or alpha variant) that emerged in the UK and has become dominant there and in the United States. Fauci also said the delta variant “may be associated with an increased disease severity such as hospitalization risk.”


“Delta is nastier,” William Hanage, an associate professor of epidemiology at the Harvard T.H. Chan School of Public Health, said Tuesday in a series of tweets. He said that if unvaccinated people get it, “I am sorry but the virus is more likely to land you in hospital.” Hanage said the data are not in yet on the outcomes for people who are hospitalized with the variant.

Will I be protected by getting vaccinated?

Yes, the experts say. Fauci referred to data from Britain’s public health agency that shows two doses of the vaccines made by Pfizer and AstraZeneca are 88 percent effective in preventing symptomatic disease caused by the delta variant.

The Pfizer vaccine is one of three being administered in the United States. Fauci also told The Washington Post in an interview that the Pfizer data would be similar for the two-shot Moderna vaccine also being administered in the United States, which, like the Pfizer vaccine, uses mRNA technology.

Dr. Paul Sax, clinical director of the Division of Infectious Diseases at Brigham and Women’s Hospital, said Wednesday, “The evidence so far is that those who have received two shots of the Pfizer (and hence Moderna) vaccines likely will be protected.”

Fauci did not discuss at the briefing the possible effectiveness of the third US vaccine, the one-shot Johnson & Johnson vaccine. In an e-mail, Sax said, “One theoretical concern is that those who have received the J&J vaccine might not be as protected, as it already had a lower efficacy than the Pfizer and Moderna vaccines in clinical trials, and that was before the emergence of this variant.”


“We’ll have to watch for this carefully,” he said.

If the vaccines work, what’s the problem?

The problem is that not everybody has been vaccinated. And the arrival of the variant comes at a time that the rate of vaccinations nationally is slowing - and Biden’s goal of getting 70 percent of American adults vaccinated by July 4 is looking harder to reach.

The delta variant “bears watching,” Dr. Shira Doron, an infectious disease physician and hospital epidemiologist at Tufts Medical Center, said Wednesday in an e-mail. “In pockets of the state and country that are unvaccinated, it can certainly cause outbreaks.”

Hanage noted “inequities in vaccination and vaccine access” and warned, “Delta is here already. It will transmit in poorly vaccinated communities once it gets to them. Those infected are more likely to suffer severe disease than previously.”

Fauci said the arrival of the delta variant was another “powerful argument” for getting vaccinated. And Biden himself tweeted Tuesday, “If you’re young and haven’t gotten your shot yet, it really is time.”

Material from Globe wire services was used in this report.

Martin Finucane can be reached at