The coronavirus's highly contagious delta variant has dominated headlines in recent weeks—but CDC and the World Health Organization (WHO) have also labeled another variant, beta, a "variant of concern," and research suggests it could evade some vaccine protection.

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What is the beta variant?

The beta variant, also known as B.1.351, was first identified in South Africa in 2020, where—at one point—it accounted for more than 95% of sequenced virus samples, the New York Times reports. According to CNBC, the beta variant has since been reported in more than 130 countries.

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However, despite its wide reach, the variant is not as prevalent as delta. The beta variant currently accounts for about 7% of virus samples in Spain, 6% in South Africa, 4% in France, and just 0.1% in the United States. In comparison, the United States, the delta variant accounts for about 83% of Covid-19 cases.

Nonetheless, experts have said that when compared to earlier variants of the coronavirus, the mutations on the beta variant make it more transmissible, with greater antibody resistance.

Specifically, the variant has three mutations of note on its spike protein—E484K, K417N, and N501Y—CNBC reports. The E484K mutation appears to help the virus evade antibodies, which may make it more resistant to vaccines and monoclonal antibody treatments, the New York Times reports, while another of the mutations enables it to bind more tightly to human cells.

Overall, CDC estimated that beta variant is roughly 50% more infectious than the original coronavirus strain, and according to a preprint study cited by WHO, the variant carries a higher risk of hospitalization, ICU admission, and death.

How well do vaccines work against the beta variant?

According to WHO, Covid-19 vaccines currently available in western nations appear to be effective at preventing "severe disease" from the beta variant. However, there is "possible reduced protection against symptomatic disease and infection."

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For instance, studies in Qatar have found that two doses of the Pfizer-BioNTech vaccine are 72% to 75% effective at preventing infection with the beta variant, two doses of the Moderna vaccine are about 96% effective at preventing infection, and the full course of either vaccine is more than 95% effective at preventing severe illness and death.

Similarly, a clinical trial in South Africa found that the Johnson & Johnson vaccine is 64% effective at preventing infection and 82% effective at preventing severe disease, the Times reports.

Delta vs. beta

Lawrence Young, a virologist and professor of molecular oncology at the Warwick Medical School at the United Kingdom's University of Warwick, said, "[W]e know that the delta variant outcompetes beta when it comes to transmissibility, but beta's been hovering in the background for quite a while."

Laith Abu-Raddad, an infectious disease epidemiologist at Weill Cornell Medicine-Qatar, who led both the Qatar studies, said that while "breakthrough infections with beta are not uncommon, these breakthrough infections are mild, and it is very rare for someone fully vaccinated to require serious hospitalization or to die after a beta breakthrough infection."

As a result, according to Young, beta is primarily a concern for unvaccinated or partially vaccinated populations. "[A]ll the data we have on [beta's vaccine resistance], particularly from South Africa, does raise concerns about that [the beta variant being able to avoid vaccines in a population that's only partially vaccinated or not vaccinated," he said. (Anthes, New York Times, 7/19; Ellyatt, CNBC, 7/21)