banner
Health Team

Delta variant as contagious as chicken pox, but what does that mean?

Posted July 30, 2021 3:04 p.m. EDT
Updated July 30, 2021 6:22 p.m. EDT

— North Carolina is reeling with a surge of new coronavirus cases and the Delta variant, which first emerged in India, is largely to blame for skyrocketing numbers. On Friday, the state added 3,199 new cases.

A confidential document from the Centers for Disease Control said Delta is more transmissible than the common cold, the 1918 Spanish flu, smallpox, Ebola, MERS and SARS. It’s that document and the science behind it that led to new safety protocols, including encouraging even those that are vaccinated to wear masks again when indoors.

"To put it in the simplest terms, the Delta variant appears to be about three times more contagious than the previous variants of this virus were," Dr. David Montefiori of the Duke Human Vaccine Institute told WRAL News.

In scientific terms, viruses are assigned what’s called an R Naught value. It’s the average number of people an infected person spreads the virus to. The earlier versions of the coronavirus had a value of about 2.5. There are some studies that suggest the R Naught value of the Delta variant is as high as 8. That means, on average, one infected person spreads the virus to 8 others.

The internal CDC document also said the Delta variant is as contagious as chickenpox. According to Johns Hopkins data, chickenpox has an R Naught value of 9.5, so the two are fairly close.

WRAL Data Trackers went through months of recently released scientific research on the Delta variant. While not all of it has been peer reviewed, meaning it shouldn’t be used to make medical decisions, the "rough drafts" have plenty of convincing and concerning results.

The first involved studying viral loads in people infected with the Delta variant compared to the first two versions of the coronavirus. When testing to see if people have the virus, samples are amplified until a detectable amount of virus is created. It’s called cycling. The more cycles you run, the lower the viral load in that sample. Earlier versions of the virus had average cycle thresholds between 31 and 35. For the Delta variant, that number drops to about 25, meaning the viral load in infected patients is 1,000 times higher.

Scientists say the huge difference may explain why even the vaccinated who are infected with the Delta variant can transmit it to other people. "It appears as though people who are infected with the Delta variant are shedding more virus," explains Montefiori. "So if you’re an unvaccinated person, and you’re around a person who is infected with the Delta variant, there’s more of that virus in that airspace around that infected person than there was before when people were infected with earlier variants of the Coronavirus. So you’re more likely to contract that virus, if you’re, you know, in in that airspace."

So-called breakthrough cases, where the vaccinated test positive, are rare, and they pale in comparison to the number of unvaccinated people who are getting Covid.

The CDC document said there are 35,000 symptomatic infections each week among the more than 160 million Americans who are vaccinated. More than 5,000 have died. Research shows a large percent of the vaccinated who die from Covid or become severely ill were immunocompromised prior to their infections.

If I’m going to get the virus anyway, why get the vaccine?

"They are much less likely to get infected," says Montefiore about those who are vaccinated. "And far less likely to get sick and die. That’s something to remember, the vaccines remain very, very effective against the Delta variant."

Again, WRAL Data Trackers found research to back that up. One study showed after the second dose of the Pfizer vaccine, it was 87% effective against the Delta variant (compared to 93% against the original coronavirus). Those same researchers found just one dose of Moderna was 72% effective against Delta. Unfortunately, they didn’t have findings for the efficacy after the second dose or statistics about the one-shot Johnson & Johnson vaccine. The first shot of Pfizer and Moderna also significantly lowered the chances of hospitalization or death of Delta patients.

While science shows the Delta variant is more transmissible in the air, there are still unanswered questions about other types of spread. Montefiore doesn’t think surface spread will be much different than earlier virus versions.

"I wouldn’t expect it to be much different than it was with the earlier variants, that risk was relatively low," he said. "You might expect it to be somewhat higher with the Delta variant, but overall, still low."

Montefiore understands the frustration of going backward as we continue to try to beat this pandemic. He also understands those who are frustrated with the ever-changing guidance. However, he says that’s more of a product of a changing virus.

"The answers that we’ve got from the scientists with this virus have come very quickly throughout the entire pandemic. I mean, the learning curve has been a very sharp curve. It’s been quite remarkable. But you know, every time there’s a new question, in every time there’s a new variant, there’s a whole new set of new questions. It takes time to get those answers," he said.

For now, Montefiore hopes reluctant Americans will get vaccinated and follow masking guidelines. Not doing either could come with a huge price.

"Every time we see a new variant, it’s more contagious than the previous one," he said. "I hope that that’s as bad as it’s going to get. And there’s always the next one that’s worse. When it’s going to end, we really don’t know. But the important thing is to put a stop to this pandemic. And the best way to do that is by vaccination."

Our commenting policy has changed. If you would like to comment, please share on social media using the icons below and comment there.