People Are Talking About A 'Double Mutant' Variant In India. What Does That Mean?

By Michaeleen Doucleff

Published April 24, 2021 at 7:25 AM EDT

Like all viruses, the coronavirus mutates. Above: In this depiction of the the South African coronavirus variant B.1.531, the thin yellow band around the rim of indicates a mutation site. The virus spike (red) is attaching to a human cell receptor (blue).

India is in the midst of a devastating second wave of COVID-19. For the past several weeks, cases and deaths have skyrocketed. The country is recording more than a quarter million cases per day.

The situation in India sounds remarkably similar to what has happened in Brazil, South Africa and now also Iran, says infectious disease scientist Kristian Andersen at Scripps Research Institute. "These countries already had a lot of people infected [in the first wave], and there was a sense that the country had reached some level of herd immunity," he says. But then, over time, as people's immunity waned, more contagious variants came along and sparked another surge.

"I think that's what's happening in India," Andersen says.

One of the new variants circulating in India — and causing concern — is referred to as the "double mutant." Here's what we know about it, so far.

Why do people call this new variant the "double mutant?"

Officially, the variant is called B.1.617, but many people and media outlets (including NPR) have referred to the variant as the "double mutant." That's because B.1.617 has two key mutations that have cropped up in two other infamous strains.

But scientifically, the term "double mutant" makes no sense, Andersen says. "'SARS-CoV-2 mutates all the time. So there are many double mutants all over the place. The variant in India really shouldn't be called that."

Like the other variants of concern, B.1.617 contains not just two mutations, but more than a dozen.

That all said, there's a reason why the term "double mutant" came about. First, B.1.617 has a mutation (labeled L452R) that's also present in the dominant strain in California. Second, B.1.617 has a similar mutation (called E484Q) as the one present in the variants first detected in South Africa and Brazil (that mutation is called E484K).

So in a nutshell, B.1.617 has two "famous" mutations. But it also has about 11 other ones as well.

Is this variant "double concerning?" Is it more contagious?

Preliminary evidence suggests that B1.617 is more contagious than previous strains of the virus. A study published Tuesday found that the L452R mutation may enhance the ability of viruses to infect human cells in the laboratory. The variant in California, which carries this same mutation, is about 20 percent more transmissible than older strains of the virus.

B.1.617 is also spreading quickly in India. Over the past few months, it has become the dominant strain in the state of Maharashtra, Nature has reported.

But, Andersen says, no one knows for sure if B.1.617 is more transmissible and thus driving India's surge. "We also know the B.1.1.7 [the variant first detected in the U.K.] is circulating in India, and we know that P.1. [the variant first detected in Brazil] is also circulating there, too. So they could also play a role in this surge. We simply don't have the data yet."

Will the vaccines still work against B.1.617?

Several studies have linked the two key mutations in B.1.617 with an increased ability for the virus to evade the immune system. So, most likely, COVD-19 vaccines will still work against B1.617, but they could be slightly less effective, Cambridge University's Ravi Gupta said on Twitter: "Likely vaccines will protect against severe illness and death but not against infection in those [people] with poorer immune responses."

There are also signs that people who have already had COVID-19 can be reinfected more easily with this strain, Gupta wrote, especially over time, as their natural immunity wanes. These reinfections may be driving this second, explosive surge in India.

"The fact that case numbers fell in India during 2020 with limited social distancing makes me worry that the decline was related to reduced numbers of susceptible people," Gupta wrote, because so many Indians caught COVID-19 and became immune during the first wave. "And ... this [second] wave is driven by waning immunity + evasion, as suggested by B.1.1.7 and B.1.617 dominance."

If B1.617 does increase the chance of reinfection (or breakthrough infections in people who have been vaccinated), then this new variant could drive surges in other parts of the world where a population's immunity, natural or vaccine-derived, is on the decline.