CDC recognizes Delta as a 'variant of concern' in the US. Meantime, a new version, called Delta Plus, has emerged.

You're probably hearing and thinking about COVID-19 less these days, and there's a good reason for that: Cases of the virus continue to fall as more people in the US are vaccinated. But there's been a lot of buzz about a COVID-19 variant called Delta that has plenty of people-including infectious disease experts-talking.

The US Centers for Disease Control and Prevention (CDC) now considers Delta a "variant of concern," meaning it poses an increased risk of transmission and severe disease. It accounted for more than 20% of COVID-19 cases in the US as of June 19, per CDC data.

During a briefing of the White House COVID-19 response team earlier in this month, Anthony Fauci, MD, director of the US National Institute of Allergy and Infectious Diseases, said that the variant has potential to spread more rapidly. "We cannot let that happen in the United States," he said, pointing to the UK, where the variant has caused a resurgence in cases, as a "powerful argument" for more vaccination.

In the UK, Dr. Fauci said, the Delta variant has become the dominant strain, replacing B.1.1.7 (now called the Alpha strain). It's also driving new cases in people ages 12 to 20.

Dr. Fauci said that the Delta variant may be "associated with increased disease severity" when compared to the original SARS-CoV-2, the virus that causes COVID-19.

Eric Topol, MD, founder of the Scripps Research Translational Institute, said on Twitter that the Delta variant is "the worst we've seen so far."

British Health Secretary Matt Hancock also said in a press conference that Delta is around 40% more transmissible than SARS-CoV-2, meaning it can spread faster and easier than the original strain of COVID-19.

And now there are reports of a new version of the Delta variant, dubbed Delta Plus, circulating in several counties, including the UK, India, and US.

It's a lot to take in, especially as you're starting to get used to some sense of normalcy again. Here's everything you need to know about Delta based on the data so far.

Where did the Delta variant originate?

The Delta variant, aka B.1.617.2, was originally detected in India in December 2020, according to the CDC. It's actually a mutation or sub-variant of B.1.617, the so-called "double mutant" strain that got plenty of attention in April.

"As these viruses mutate and develop, they look like your family tree," John Sellick, DO, an infectious disease expert and professor of medicine at the University at Buffalo/SUNY, tells Health. "This particular sub-variant has wrecked havoc in India." And now, it seems, it's spreading across the globe.

Delta Plus differs a bit from the Delta variant. It features an extra spike-protein mutation, called K417N. according to news reports.

Is the Delta variant in the US?

Yes. Currently, the Delta variant makes up more than 20% of all COVID-19 cases in the US. That's up from almost 10% just two weeks ago. It's not entirely clear when it first arrived in America.

And while cases of the new Delta Plus variant (officially B.1.617.2.1 or AY.1) have reportedly been found in the US, this version of the Delta variant does not yet appear as a separately identified category in CDC's description of COVID variants. Still, is captured attention this week after officials in India declared it to be a variant of concern, per the New York Times.

Why is the Delta variant so concerning?

The Delta variant has several mutations on the spike protein of SARS-CoV-2, which can help it spread more easily than other forms of the virus. The CDC specifically says that this variant is more transmissible and poses a "potential reduction" in the effectiveness of the COVID-19 vaccine and the ability of some monoclonal antibody treatments to work against the virus.

The CDC previously regarded the Delta variant as a "variant of interest" but now considers it a "variant of concern" in the US based on evidence of its increased transmissibility and disease severity (as measured by hospitalizations and deaths).

"A variant like this can rapidly take over and become the primary strain circulating in that region," Stanley Weiss, MD, professor of medicine at the Rutgers New Jersey Medical School and professor of biostatistics and epidemiology at the Rutgers School of Public Health, tells Health. "That indicates that a variant has survival advantages. In places such as India where we've seen so many people infected and so much disease, there's evidence that this can spread quickly."

Experts are also concerned because "the variant has the potential to at least partially evade the protection of the vaccine," William Schaffner, MD, an infectious disease specialist and professor at the Vanderbilt University School of Medicine, tells Health. He compares Delta to B.1.351 (now called Beta), which was originally detected in South Africa. "There is a chance that this can make you sick, even if you're been vaccinated," Dr. Schaffner says.

Delta is also potentially problematic because "it's clear that young people are at risk," including those who aren't yet eligible for the COVID-19 vaccine, Dr. Weiss says.

As for Delta Plus, CNN reports that health experts are remaining vigilant, although it's too soon to say whether the variant is any more transmissible than other strains.

What are the symptoms of the Delta variant?

Symptoms of the Delta variant are slightly different than those of the first variant that spread through the US. "COVID is acting differently now. It's more like a bad cold; people might think they've just got some sort of seasonal cold," Tim Spector, professor of epidemiology at King's College London, explains in a video released on YouTube by the COVID Symptom Study.

He explains that the number one top symptom for those with the Delta variant is headache, and this is followed by sore throat, runny nose, and fever. "Those are not the old, classic symptoms," Spector says. "Number five is cough, [though] it's rarer." He adds that loss of smell isn't among the top 10 reported symptoms for those with the Delta variant.

Anecdotally speaking, per the Times of India, the Delta varian has also been linked with more GI issues, including diarrhea, stomach pain, loss of appetite, and nausea.

Still, there's not a lot of data on this just yet, Dr. Sellick says. He recommends keeping an eye out for the usual COVID-19 symptoms.

Are vaccines effective against the Delta variant?

Yes-ish. The CDC cites data from a study of COVID-19 cases in 44 counties in California, which found that COVID-19 variants with an L452R mutation, which Delta has, can cause a two-fold reduction in neutralizing titers in people who have been fully vaccinated against COVID-19. (Neutralizing titers help target and take out a virus, and they tend to correlate with the level of protection offered by a vaccine.)

How much less protective the COVID-19 vaccines are against Delta in the real world isn't clear at this point, Dr. Schaffner says. "Even if this variant can partially evade protection of the vaccine, the more people who are vaccinated, the less apt this is to spread," he says.

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDCWHO, and their local public health department as resources.

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