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4 Things You Need to Know About Delta-Plus    

As the delta surge ebbs, attention is turning to an offshoot of the highly contagious coronavirus variant

gloved hand holding a vial with a COVID-19 strain test sample shows the word Delta+

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Delta’s summertime surge is finally abating. New cases of COVID-19 caused by the highly contagious coronavirus variant are nearly half of what they were at their peak in early September. And hospitalizations and deaths are also dwindling.

But that doesn’t mean delta’s power is fading. It still accounts for more than 99 percent of COVID cases in the U.S., according to data from the Centers for Disease Control and Prevention (CDC). What’s more, it’s giving rise to new versions of the virus, including one, called delta-plus (or AY.4.2), that’s captured the attention of experts.


Here’s what we know so far about delta’s descendant.

1. It’s an offshoot of delta

Viruses change and evolve as they replicate — that’s expected — and when one or more of these changes sticks, a variant is born.

What makes delta-plus different from the long list of other variants that have popped up since the start of the coronavirus pandemic, however, is that it’s not a variation of the original virus strain. Rather, it’s derived from delta, the dominant variant circulating throughout the globe.

“You had the original strain, and anytime a new variant came up all it had to do was outcompete that original strain. And then you had several variants all circulating more or less at the same time,” explains Richard Kennedy, professor of medicine and codirector of the Mayo Clinic Vaccine Research Group. “Nowadays, almost all of the cases, at least in the U.S. and in the U.K., are delta. So 99 percent of the variants that we're going to see now are going to be variants of delta, not variants of the original strain.”  

Because of this, the CDC refers to delta-plus as a sub-lineage. Other variants, including alpha and gamma, also have sub-lineages that are being tracked.

2. It may turn out to be more contagious than delta

Experts still aren’t sure what to make of delta-plus. What we do know is that the delta variant is highly contagious, and some data suggests it can cause more severe illness than other variants, especially in not fully vaccinated individuals, who account for about 40 percent of the U.S. population.

Delta can also evade some of the immune response that’s generated after vaccination, although the vaccines are still highly effective at preventing hospitalization and death.

“So that means any new variants, if they come from delta, they already have that background,” Kennedy says, which “makes it more likely that they're going to be a bigger problem than a variant that shows up that was a variant from the original strain.”

Preliminary research shows that delta-plus is about 10 to 15 percent more transmissible than delta, says Ashish Jha, M.D., dean of the Brown University School of Public Health.

3. Spread of delta-plus has been slow so far

Delta-plus isn’t causing too much concern yet, and its slightly higher transmissibility rate isn't alarming in itself, says Jha. By comparison, the delta variant is twice as contagious as other variants, including alpha, which was the previous dominant variant in the U.S. And information out of the U.K., where delta-plus’s presence has been slowly increasing since July, suggests that the vaccines “are holding up just fine” against it, Jha adds, though research is ongoing.

Another reassuring trait: Delta-plus shares a few mutations with other variants “that didn’t really go anywhere,” Kennedy says. “And so the general consensus is that these mutations may not provide much of an advantage to the virus.”

Nowadays, almost all of the cases, at least in the U.S. and in the U.K., are delta. So 99 percent of the variants that we're going to see now are going to be variants of delta, not variants of the original strain.

Richard Kennedy, Mayo Clinic Vaccine Research Group

Virus strains that are “a little heartier” than their peers — maybe their mutations allow them to replicate faster upon infection, or pack more of a punch when confronted with antibodies — take over and spread. But delta-plus “does not seem to be spreading very quickly,” Kennedy points out. In October, delta-plus accounted for about 6 percent of all cases in the U.K.; tracking sites show that number may be around 14 percent now. Only a few cases have been spotted in the U.S.

That said, delta-plus is still managing to spread, even with delta in the mix, meaning it likely has an edge on delta. But “it's too early to tell if it's a lot better or not,” Kennedy says.

CDC Director Rochelle Walensky, M.D., has said the CDC is “continuing to track lineages and sub-lineages of delta and all other variants,” as well as their potential impact on COVID treatments and vaccines. But for now, there is “no evidence” of an immediate threat.

“I think of this as a variant of a little bit of concern, but certainly not anything that I think represents a game changer in terms of our strategy and approach,” Jha adds.

4. Vaccines are key to forestalling new variants  

The vaccines are crucial to keeping the COVID curve trending in the right direction and to avoid giving rise to new and potentially more destructive variants and lineages, experts say.

The reason? “The only time the virus can create variants is when it's inside a human being, inside a cell creating new viruses,” Kennedy says.


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Though the COVID vaccines are not 100 percent effective at preventing a coronavirus infection, studies show that fully vaccinated people are significantly less likely to be infected. “If we can reduce the number of cases significantly, we've reduced the chance of having a delta-plus-plus or whatever we decide to name the granddaughter of delta,” Kennedy says.

Other precautions can also help stymie the emergence of new variants: Wear a mask when you are in crowded, indoor settings; wash your hands often; and if you’re due for a booster, get it. “What you have to do is put multiple layers of protection in place,” Kennedy adds.