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Vaccines Are Slightly Less Effective Against B.1.617 Variants of COVID-19

Illustration of white hands holding a vial labeled "vaccine" surrounded by red COVID virus particles on a blue background.

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Key Takeaways

  • Two preliminary studies have found that the B.1.617.1 and B.1.617.2 variants of the SARS-CoV-2 virus appear to be more resistant to the COVID-19 vaccines than the original virus, but that the vaccines are still very effective. 
  • The two variants hit India in February, where vaccination rates are still low.
  • Experts say that getting as many people as possible vaccinated against COVID-19 is the only way to stop more variants from arising and curbing the pandemic for good.


A preliminary report shows that the B.1.617.1 coronavirus variant is nearly seven times more resistant to antibodies. This holds true whether the antibodies are from vaccines or previous infection with COVID-19.

However, researchers also noted that 80% of the blood samples studied were able to neutralize the B.1.617.1 variant—which means that getting as many people vaccinated against the virus is key to stopping the pandemic.

Variant Resistance

According to the Centers for Disease Control and Prevention (CDC), there are four versions of this variant: B.1.617, B.1.617.1, B.1.617.2, and B.1.617.3.

All four have been labeled as Variants of Interest—a category of variants that may have mutations that could reduce the effectiveness of vaccines or antibodies from previous COVID-19 infections, reduce the effectiveness of treatment, increase transmissibility, or increase the severity of the disease.

The new study, which was conducted by the Emory University School of Medicine, Stanford University School of Medicine, and the Vaccine Research Center at the National Institute of Allergy and Infectious Diseases (part of the National Institutes of Health), found that the antibodies produced by infection or vaccination are able to block the variant—just not as well as they do other variants.

In a briefing for reporters, Mehul Suthar, PhD, assistant professor with the Emory Vaccine Center and the Department of Pediatrics at Emory and an author of the study, said that the results raise concerns that individuals who were previously infected or vaccinated could be infected with the variant.

Suthar tells Verywell that its seven-fold level of vaccine resistance puts the B.1.617 variant at the same level as the strain that was first detected in South Africa (which has a similar mutation).

A Small Decrease In Vaccine Effectiveness

A second preliminary study, which was conducted by Public Health England and Guys and St. Thomas’s Hospital NHS Trust in London, also found a small decrease in the effectiveness of the Pfizer/BioNTech and AstraZeneca vaccines against the variant.

For the study, which was also published as a preprint, the researchers used data from genetically sequenced cases of COVID-19.

After one dose of the vaccine, the researchers found “modest differences in vaccine effectiveness with the B.1.617.2 variant." However, they noted that the differences in effectiveness were more marked in people who only had one dose.

The researchers concluded that vaccination campaigns should be maximized to ensure that more people receive both doses of the vaccines.

What Is Preprint Research?

Both studies were published as preprints, which means that they were not peer-reviewed.

Peer review is a process in which a scientific paper is evaluated by other experts to look for any flaws in the research or the study's conclusions.

Preprints allow information on research to be presented before it can be reviewed, but at the risk that the paper could be withdrawn later if problems are found.

Vaccination Helps Stop Variants

Suthar says that vaccination is critical to halting the spread of COVID variants. “The more these viruses infect, the more they replicate, the more they spread, the greater the opportunity these viruses have to mutate and to generate new variants,” he says.

Mahul Suthar, PhD

The more these viruses infect, the more they replicate, the more they spread, the greater the opportunity these viruses have to mutate and to generate new variants.

— Mahul Suthar, PhD

Starting in February, the B.1.617.1 and B.1.617.2 variants of SARS-CoV-2 hit India—which is a relatively low vaccination rate—hard. According to data collected by the New York Times, the surge led to 27 million infections and strained India's healthcare system to the limit.

“My understanding is that the B.1.617.2 is one of the more dominating infections that are occurring in the UK, compared to the B.1.1.7, [the variant that emerged in Britain]” Suthar says. “So, it looks like the B.1.617.2 may be more transmissible than other variants.”

Testing Other Vaccines

B.1.617.1, B.1.617.2, and B.1.617.3 have been detected in the United States and other countries. In Britain, the B.1.617.2 variant is outpacing other strains of the virus.

Suthar also says that it is still not clear whether these variants cause more serious cases of COVID than other variants.

Suthar and his colleagues are currently conducting similar studies of how effective the Johnson & Johnson and Oxford/AstraZeneca vaccines—which use a viral vector rather than messenger RNA (mRNA) to get the body to make antibodies—will work against COVID-19.

What This Means For You

The preliminary results of two studies have shown that the B.1.617.1 and B.1.617.2 variants of the COVID-19 virus are more resistant to vaccines. However, the available COVID vaccines are still very effective against them. Making sure that everyone is fully vaccinated is still the best way to stop the pandemic.

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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Article Sources
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  1. Edara VV et al. Infection and vaccine-induced neutralizing antibody responses to the SARS-CoV-2 B.1.617.1 variant. bioRxiv. 2021.05.09.443299; doi:10.1101/2021.05.09.443299

  2. Centers for Disease Control and Prevention (CDC). SARS-CoV-2 Variant Classifications and Definitions. Updated June 1, 2021.

  3. Bernal JL, Andrews N, Gower C, et al. Effectiveness of COVID-19 vaccines against the B.1.617.2 variant. medRxiv. 2021.05.22.21257658; doi:10.1101/2021.05.22.21257658