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What to know about the highly contagious COVID-19 Delta variant

TODAY logo TODAY 6/10/2021 Maura Hohman

The Delta variant of the coronavirus, which first emerged in India, is a growing source of concern for public health experts who worry it could become the dominant variant in the U.S. in the coming weeks.

The variant, which is responsible for India's recent surge in cases, overwhelming hospitals, has already become the dominant variant in the U.K. despite the country's high vaccination rate. It's believed to be "by far the most contagious variant of this virus that we have seen throughout the whole pandemic," Dr. Ashish Jha, dean of Brown University School of Public Health in Providence, Rhode Island, told Savannah Guthrie on TODAY Wednesday.

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The Centers for Disease Control and Prevention and the World Health Organization have been tracking COVID-19 variants that may be more transmissible or lead to more severe disease, such as the one first detected in the U.K. in September. Each variant has been named after a letter in the Greek alphabet to make it easier for the public to discuss them, per the World Health Organization.

While current evidence shows COVID-19 vaccines offer good protection against the new variants, Moderna, Pfizer-BioNTech and Johnson & Johnson are developing booster shots, targeting the variants of concern.

At this stage, though, one thing remains clear: Existing methods to prevent transmission of COVID-19 are the still the most effective strategies, experts told TODAY. These include getting vaccinated, masking, or even double masking, avoiding crowds and poorly ventilated indoor spaces, and washing your hands regularly.

Here's what else you need to know about the COVID-19 variants, from symptoms, to how lethal they are and whether vaccines will work against them.

What is a variant? How does it happen?

While the existence of new variants may be worrisome to the general public, the phenomenon is "not entirely unexpected," Ben Lopman, Ph.D., professor of epidemiology at Emory University's school of public health in Atlanta, told TODAY.

"Viruses spread by replicating themselves ... and that replication process is imperfect," he explained. "The virus makes mistakes sometimes. Most of those mistakes are useless or will kill the virus. Rarely but sometimes, one of those mistakes will be beneficial. It could, for example, make the virus more easy to transmit from person to person by changing its genetics in some way."

The U.K. variant in particular, aka Alpha, which the CDC estimates has 50% increased transmission, seems to replicate more efficiently, Lopman said. This could mean that infected people are "actually producing more of the virus or shedding the virus at somewhat higher levels, and that might be what makes it more transmissible," he added.

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But viruses acquiring mutations isn't "necessarily a bad thing," Jasmine Plummer, Ph.D., associate director of applied genomics at Cedars-Sinai medical center in Los Angeles, told TODAY.

"(Viruses) want to survive," she explained. "It's not in (their) best benefit to keep killing the host, meaning the person. Near the end, (the virus might) figure out a way ... to survive by infecting more people, but the outcome of that infection is hopefully not as severe."

How many strains of COVID-19 are there?

A new strain occurs when a virus goes through one or more mutations that change its behavior in some way, but a variant develops when a virus goes through a mutation of any kind, explained Dr. Patricia Couto, an infectious disease physician at Orlando Health in Florida.

According to Lopman, "there are many variants out there," but a few are concerning because they "appear to be spreading more quickly" and could "possibly (replace) the variants that were previously dominant," he said. The Alpha variant was the dominant variant in the U.S. as of April, according to NBC News.

Here's a breakdown of the concerning COVID-19 variants, including the Delta variant, and what to know about each:

Delta variant from India

This variant is believed to have first emerged in India in October 2020. It's since spread to the U.S. and currently accounts for more than 6% of sequenced cases in the U.S., Dr. Anthony Fauci said at a recent news briefing. It also has increased transmissibility compared to other variants, according to the World Health Organization.

Alpha, U.K. variant


Video: Delta variant of COVID-19 is ‘by far the most contagious we have seen,’ doctor says (TODAY)

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The U.K. strain, called B.1.1.7, was first reported in the U.S. in late December, and it spreads more quickly and easily than other variants, according to the CDC. It is now in all 52 states and territories and is the dominant variant in the U.S. The CDC has also said it has "potential increased severity based on hospitalizations and case fatality rates."

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Beta, South African variant

This variant, known as B.1.351 or Beta, emerged independently from the U.K. strain but shares some of its mutations, according to the CDC. Data indicates that it first emerged in South Africa in October 2020 and has since spread to other countries, including the U.S. In late January, CDC director Rochelle Walensky told TODAY that it had already reached the point of community spread. This variant could also make reinfection more likely; a vaccine study in South Africa found 2% of people who'd already had a version of the coronavirus had been reinfected with a variant. It also has an estimated 50% increase transmission.

Gamma, Brazilian variant

The Brazilian variant, P.1, was first detected in mid-January in travelers to Japan from the Amazonas state of Brazil. It appears to contain mutations that raise concerns about its transmissibility and potential for reinfection, according to the CDC. Manaus, the largest city in the Amazon region, saw a surge in cases in December 2020, despite 75% of the population already having been infected by October.

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Are new COVID-19 variants, including the Delta variant, more deadly?

The Delta variant is believed to be the most contagious of the variants circulating at the moment, which as the outbreak in India shows, can lead to more death. The Delta variant may also have an increased risk of hospitalization, but this is not confirmed, the World Health Organization said in a recent report.

The Alpha strain has a "potential increased severity based on hospitalizations and case fatality rates," according to the CDC, and there is also emerging evidence that the South African strain may be more virulent, but the CDC has not confirmed that this is the case, and the same goes for the Brazilian one.

Do the new variants have different symptoms?

Currently, none of the new variants have been associated with new or different symptoms, experts told TODAY. Per the CDC, the most common symptoms of COVID-19 include:

  • Fever or chills
  • Cough
  • Shortness of breath or difficulty breathing
  • Fatigue
  • Muscle or body aches
  • Headache
  • New loss of taste or smell
  • Sore throat
  • Congestion or runny nose
  • Nausea or vomiting
  • Diarrhea

Couto also stressed that the new variants and strains also seem to result in the same wide range of illness that's come to be associated with COVID-19.

Are COVID-19 vaccines effective against these strains?

There's no evidence yet that the virus has mutated in ways that allow it to evade vaccines completely, but the research into the shots' efficacy against variants is ongoing. Moderna, Pfizer, AstraZeneca and Johnson & Johnson have all released some data on how their vaccines respond to variants.

According to a recent report from the World Health Organization, the vaccines are effective against the Alpha variant, and it's likely that they're effective against the Gamma and Delta variants, as well, but the evidence at this stage is very limited. It also appears that they can reduce the risk of severe and mild to moderate illness from the Beta variant.

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Vaccination efforts are crucial to slow the spread of variants, Jha told TODAY earlier this week.

"The good news is our vaccine seems to be holding up quite well, but the contagiousness and potentially the lethality of (the Delta variant), that's really what's concerning many of us," he said. "We still have a lot of Americans who have not yet gotten vaccinated, they are extremely very vulnerable. ... The data that's emerging suggests that if you have been vaccinated, you're going to be fine ... but my big concern is a large pockets of America that remain unvaccinated, including a group of older Americans who still have not gotten the shot, they're particularly vulnerable."

Back in April, during a White House briefing about variants, Walensky recommended "everybody ... roll up their sleeves as soon as a vaccine is available to them, because we see it working."

Where are the travel bans due to coronavirus variants?

According to the CDC, there are COVID-19-related travel restrictions for non-U.S. citizens who visited one of the following countries within 14 days of seeking entry to the U.S.:

  • India
  • U.K. and Ireland
  • Brazil
  • South Africa
  • China
  • Iran
  • A large portion of Europe, including Italy, France, Germany, Spain, Scandinavia and more
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How might variants effect the timeline for herd immunity?

The fact that these variants exist and are spreading doesn't automatically lengthen the path to herd immunity, Vermund said. But it does make getting vaccinated against COVID-19 and adhering to safety practices that much more influential in the timeline for getting back to normal.

"If we can get broader adherence to prevention messages and drive down (COVID-19) rates, even if we have these new strains circulating, we may be able to control the virus until we can get everybody vaccinated," he said. "If we just flagrantly flaunt the prevention messages, then, sure, the new strains, if they're more infectious, will affect more people and make things bad again."

This article was updated on June 10, 2021.

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