In-Depth: What is 'delta plus' and what makes it different from the delta variant of COVID-19?

Virus Outbreak Variant
Posted at 4:13 PM, Jul 07, 2021
and last updated 2021-07-07 20:31:11-04

SAN DIEGO (KGTV) -- As the delta variant spreads in California, scientists have detected more than 200 cases of a new offshoot that may be even stronger: a sublineage nicknamed “delta plus.”

Delta plus has all the hallmark mutations of its parent variant plus one notable mutation in its spike protein. In previous studies on other variants, this mutation helped fortify the pathogen against protective antibodies.

“This particular [mutation] changes its shape a little bit to evade our antibodies,” said UC San Diego virologist Dr. Davey Smith. “Somebody gets vaccinated, they make a human immune response, and this virus is able to evade that a little better than the previous strains.”

The mutation is at the 417th position in the virus’ genetic code, known in the scientific community as K417N. It first gained prominence in the beta variant from South Africa.

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Delta, the parent variant emerged in India and is now circulating worldwide, is already somewhat more resistant to vaccine protection than previous strains and about twice as transmissible, raising concerns that delta plus could be even more virulent.

In India, where the delta variant is already responsible for 90 percent of new infections, health officials called for even stricter containment, testing and tracing efforts two weeks ago in areas where delta plus has emerged.

The Indian government said there’s evidence delta plus is more transmissible and more elusive to antibody treatments, and classified it as a separate “variant of concern.”

Delta plus is so new, there isn’t much data on it, but it has been found in at least 15 countries and 17 U.S. states, according to the database GISAID.

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Despite concerns about its power, it’s not nearly as prevalent as the standard form of delta. There are only about 500 sequenced cases worldwide shared on GISAID since it first emerged in March. The same database shows more than 120,000 cases of the standard delta variant, according to

As of Wednesday, there were 258 sequences of delta plus documented in the U.S., according to GISAID, of which 210 were in California.

Currently, the World Health Organization and the Centers for Disease Control and Prevention do not distinguish between cases of delta and delta plus. The scientific community tracks two flavors of delta plus, AY.1 and AY.2, and both are included in the agency's overall assessments of the delta variant.

However, the CDC said it’s continuing to gather data to determine if delta plus should be classified separately.

Overall, studies show the vaccines in the US. are still effective against the parent delta variant, but not at the same 95 percent efficacy level seen during clinical trials.

A British study in May found two doses of the Pfizer vaccine were 88 percent effective against delta. A Scottish study in June found the vaccine was 79 percent effective. A Canadian study put the efficacy at 87 percent.

A study released this week from Israel found the Pfizer vaccine was just 64 percent effective against delta.
Dr. Smith said the shifting numbers should be expected because the studies were done outside of a controlled, clinical trial.

“They were done with different populations, with different timing, and different ways of collecting data,” he said.

These studies examined so-called breakthrough infections, where a vaccinated person develops symptoms, a small sample size to begin with.

“The good news in all these studies is that the people don't go on to develop severe COVID-19 or need hospitalization,” he said.

Dr. Smith said the vaccines clearly work against delta and will likely work against delta plus.

Health officials in England said June 25 that “very preliminary results” from a small number of vaccine recipients are “reassuring, however further testing is required.”