What Is the B.1.617.2 Variant?

What to know about this COVID-19 mutation, also known as the Delta variant

All viruses develop mutations and variants, and the SARS-CoV-2 virus, which causes COVID-19 infection, is no different. Since the start of the pandemic, multiple variants have developed.

One of these variants, B.1.617.2, also known as the Delta variant, has emerged. Initially discovered in India in December 2020, it has now spread across the globe.

Young woman getting vaccinated

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Where B.1.617.2 Has Spread

After starting in India in 2020, the B.1.617.2 variant became the dominant strain in that country. It quickly began to spread and has been found to infect people in over 130 countries. In addition to being the dominant strain in India, it is also the dominant strain in the United Kingdom.

Spread in the United States 

The B.1.617.2 variant was first found in the United States in March 2021 and has now been found in all 50 states. The B.1.617.2 variant is currently the dominant strain in the United States. As of August 7, 2021, the B.1.617.2 variant was responsible for more than 90% of U.S. COVID-19 infections.

Why Do Viruses Mutate?

It is common for all viruses to mutate. When a virus enters the body, it begins to make copies of itself.

Sometimes during this process, mistakes (mutations) are made in the copies, which can make it easier for the virus to invade the cell. When this same mutation continues to further copy itself, a variant of the virus forms.

Is the B.1.617.2 Variant More Contagious?

The B.1.617.2 variant is more contagious than the original COVID-19 virus—estimated to be at least 60% more contagious than the original strains.

The infectiousness of a virus is measured by an R number, or the number of people an infected person will give the virus to. For example, if the R is 1, an infected person is likely to give it to one other person; an R of 5 means an infected person is likely to transmit it to five other people.

Preventing Transmission

Precautions to prevent transmission of the B.1.617.2 variant are the same for the original COVID-19 virus and should continue to be followed. If you are unvaccinated against the virus, the following precautions should be followed:

  • Stay 6 feet apart from others who don’t live in your household.
  • Wear a mask that covers your mouth and nose.
  • Practice good hand hygiene by washing hands often or using hand sanitizer regularly.

If you are fully vaccinated, the Centers for Disease Control and Prevention (CDC) have released updated guidance that it is safe to go without a mask and physical distancing. However, local regulations should be followed.

Risk of Reinfection

There is currently limited data on breakthrough infections—or COVID-19 infections in people who have been vaccinated against COVID-19 or who have had COVID-19 infection previously. However, one study of a COVID-19 outbreak in July 2021 showed that of the 469 cases, 74% occurred in fully vaccinated persons. Based on these findings, it's unclear whether the Delta variant will lead to an increase in breakthrough infections.

Is the B.1.617.2 Variant More Severe?

Research is still ongoing, but in a study in Scotland of people infected with the B.1.617.2 variant, they experienced a higher rate of hospitalization than those who had been infected with other strains of COVID-19.

Will Vaccines Work Against the Delta Variant?

At this time, it appears that those who have been fully vaccinated against COVID-19 infection should be at reduced risk of becoming infected with the B.1.617.2 variant.

A study published in The New England Journal of Medicine found the Pfizer/BioNTech and AstraZeneca vaccines to be 88% and 67% effective, respectively, against the Delta variant after two shots. Other current studies (which have yet to be peer-reviewed) suggest one dose of the Moderna vaccine is 72% effective at preventing symptomatic disease caused by the Delta variant and the Johnson and Johnson vaccine is up to 71% effective in preventing hospitalization.

With more studies underway, it's still too soon to know if vaccine boosters will be required in the future.

Are Kids More at Risk for the Delta Variant?

As there are no currently approved vaccines for children younger than 12 years old, kids are at risk of becoming infected with the B.1.617.2 variant. As it is a more contagious strain, kids will continue to be at risk of catching it. In countries such as the United Kingdom, kids were found to have higher rates of infection.

A Word From Verywell

Experts are worried about the spread of the B.1.617.2 variant throughout the United States. As this variant is more contagious, it has the potential to infect many people.

Getting a vaccine against COVID-19 is the best way to protect yourself against this and other strains of the virus. Check with a healthcare provider to be sure the vaccine is safe for you to get. Increasing vaccination rates in the United States and around the world is the best way to decrease the spread of COVID-19.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

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  1. Centers for Disease Control and Prevention. SARS-CoV-2 variant classifications and predictions. Updated July 20, 2021.

  2. World Health Organization. WHO Director-General's opening remarks at the media briefing on COVID-19 – 30 July 2021. Published July 30, 2021.

  3. Dagpunar J. Interim estimates of increased transmissibility, growth rate, and reproduction number of the Covid-19 B.1.617.2 variant of concern in the United Kingdom. MedRxiv. Preprint posted online June 3, 2021. doi:10.1101/2021.06.03.21258293

  4. Centers for Disease Control and Prevention. COVID data tracker.

  5. Cleveland Clinic. What to know about the latest COVID-19 variant and other coronavirus mutations. Published August 10, 2021.

  6. Yale Medicine. 5 things to know about the Delta variant. Published August 13, 2021.

  7. Centers for Disease Control and Prevention. How to protect yourself & others. Updated July 26, 2021.

  8. Centers for Disease Control and Prevention. When you've been fully vaccinated. Updated July 16, 2021.

  9. Brown CM, Vostok J, Johnson H, et al. Outbreak of SARS-CoV-2 infections, including COVID-19 vaccine breakthrough infections, associated with large public gatherings — Barnstable County, Massachusetts, July 2021. MMWR Morb Mortal Wkly Rep. 2021;70(31):1059-1062. doi:10.15585/mmwr.mm7031e2

  10. Lopez Bernal J, Andrews N, Gower C, et al. Effectiveness of Covid-19 vaccines against the B.1.617.2 (Delta) variant. N Engl J Med. 2021;385(7):585-594. doi:10.1056/NEJMoa2108891

  11. New York Times. New data suggest J. & J. vaccine works against Delta and recipients don’t need a booster shot. Updated August 9, 2021.