- The Delta variant appears to be more transmissible than any other coronavirus strain.
- Some experts fear that the variant may result in more breakthrough cases in vaccinated people.
- Others are concerned that Delta may develop into even more dangerous mutations.
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Researchers have long been concerned about a coronavirus variant that is more dangerous than the original virus in three important ways: It would be more transmissible, result in more serious disease, and avoid protection against existing vaccines.
“The nightmare here is a variant that ticks all three boxes,” said Bob Wachter, president of the Department of Medicine at the University of California, San Francisco.
No previous variant, he said, has controlled more than one or two. But the Delta variant, first identified in India in February, has come closest to controlling all three.
“Data today says that this variant gets a full check box for more contagious, probably gets a check box for more serious ones and at least gets a partial check box for immune evasion. And that̵
The Centers for Disease Control and Prevention branded Delta a “concern variant” Tuesday.
“Delta is a superspread variant, the worst version of the virus we’ve seen,” tweeted Eric Topol, director of the Scripps Research Translational Institute, on Tuesday.
While Delta undoubtedly poses the greatest threat to unvaccinated people, some experts are concerned that it could result in more breakthrough diseases – cases of COVID-19 diagnosed at least two weeks after someone is fully vaccinated.
“That’s the concern – that you’re more likely to get COVID from the same exposure than you would have been before,” Wachter said. “And it’s more likely that if you have COVID, you have a more serious case.”
Other experts are also afraid that the strain may develop further into something more dangerous, as Delta’s high transmissibility allows it to spread easily among unvaccinated people and therefore continue to replicate and mutate.
“The worst case scenario is if Delta mutates into something completely different, a completely different animal, and then our current vaccines are even less effective or ineffective,” said Vivek Cherian, an internist in Baltimore.
Delta is the most transferable strain yet
Research from Public Health England suggests that the Delta variant is associated with a 60% increased risk of transmission in the household compared to Alpha – the variant discovered in the UK. Alpha is already about 50% more transmissible than the original strain, the CDC said.
In other words, “Alpha is the original, as Delta is for Alpha,” Wachter said.
Researchers in Scotland, meanwhile, found that becoming infected with Delta doubles the risk of hospitalization compared to Alpha.
But for the most part, Delta has not drastically challenged vaccines. Public Health England analyzes have shown that two doses of Pfizer’s vaccine are still 96% effective in preventing hospitalizations – and 88% effective in preventing symptomatic COVID-19 – from Delta cases. Meanwhile, two doses of AstraZeneca’s vaccine are approximately 92% effective in preventing hospitalizations and 60% effective in preventing symptomatic COVID-19 from Delta.
But that effect does not come after just one dose: a single shot of either Pfizer’s or AstraZeneca’s vaccines was only 33% effective in preventing symptomatic COVID-19 from Delta.
“The fact that three weeks after your first dose you are only 30% protected – against the original you were 80% – says that this thing has figured out how to at least partially avoid the immune system,” Wachter said.
It is also possible, he added, that vaccine protection could “wear out faster.”
Does Delta make more breakthrough infections?
Although variants are responsible for the majority of breakthrough infections, it is very rare to get COVID-19 after full vaccination: a CDC report from May showed that only 0.01% of vaccinated Americans became ill.
Even when it comes to Delta, Cherian said, “my guess is that you do not really have to worry about groundbreaking infections.”
But Wachter fears Delta may turn a mild breakthrough case into a more serious case.
“It increases the risk that we will see more breakthrough infections and perhaps more serious breakthrough infections than I would have worried about a few weeks ago,” he said.
The biggest risk may be for elderly or immunocompromised people, he added.
“The 80-year-old who has been fully vaccinated – their level of immunity is not the same as a 30-year-old,” Wachter said.
Delta can threaten our return to normal life
Delta currently accounts for 10% of US coronavirus infections, but researchers expect it to become the dominant strain within a few weeks. Wachter said he would “start acting much more carefully” if Delta were to represent one in three or five COVID-19 cases in a given region.
“If I had become comfortable being inside without a mask in a place where I was not sure everyone was vaccinated, I would now be uncomfortable,” he added.
Cherian, on the other hand, does not believe Delta guarantees this level of caution yet – although most experts are still concerned that a more concerning variant may emerge from the fast-mutating strain.
“It’s a perfect human instinct to feel that we’ve now weathered those awful 18 months, and now we’re out of it and over it,” Wachter said. “I hope it’s true and it can turn out to be true. But the chances that it’s not true and that we’ll get more in our future to tackle have increased significantly in the last few weeks because of Delta . “