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Slowing spread, getting herd immunity just got much harder

Posted at 4:51 PM, Aug 11, 2021

Like many in her shoes, infectious disease physician Dr. Sajal Tanna is doing her best to keep up with the Delta surge. It's a sign that COVID-19 herd immunity is becoming more and more out of reach.  

"The number for the herd immunity is dependent on how easily the virus can be transmitted," Tanna said. 

Delta is a different beast — more contagious. This comes down to the R-naught, a number that shows how contagious a virus is.

"For every person that gets sick, how many people are they likely to infect," said Jason Farley, an infectious disease-trained nurse epidemiologist at Johns Hopkins University. "We thought it was around between 1.5 to two to three, depending on the estimates."

In other words, one infected person, on average, got two to three other people sick. But now, with Delta: 

"We're seeing it again that R-naught of five, six, six-plus," he said.

Meaning slowing spread and getting herd immunity just got much harder. 

Another way to put it: Think about infectious diseases on a contagious ladder with Delta. It’s about two rungs down from the likes of measles and whooping cough. For measles, experts say some 95% of folks need vaccinations for herd immunity. 

"If we mean by herd immunity, there's not going to see any COVID in your community. It may require 90, 95%, a number we probably can't get to until we start vaccinating kids," said Dr. Bob Wachter, Department of Medicine chair at the University of California San Francisco. 

Every expert Newsy spoke with across the country — East Coast, Midwest, West Coast — shared the dire concern: In this vaccine versus variants race, we’re behind. In parts of the country with higher rates, it means not fully overwhelming hospital ERs and COVID units.  

"You're seeing a much greater struggle in states like Florida or Louisiana right now because they are nowhere near herd immunity. The population is not protected.

And that's why we're seeing such a massive surge. The big concern is the spillover effect. With modern travel, it's straightforward for one part of the country to share things with another," said Dr. Nicholas Turner, an infectious diseases assistant professor at Duke University Medical Center. 

In other words, Delta means a big step back, with the slightest weak spot causing more COVID spread. 

"If we don't control this virus and if we don't get ahead of it, we will be talking about the need for not only boosters, but possibly even different vaccines moving forward," Farley said.

That doesn’t mean, though, Delta is rendering the COVID vaccines useless. Those shots could be the difference between a visit like this and one in the COVID ICU.  

"We are seeing a rise in COVID infections in both vaccinated unvaccinated people. The difference is, is that the unvaccinated patients I'm seeing are so much sicker.

Having a breakthrough infection is still really miserable, but I'm not seeing those people in the hospital, and I'm not seeing them on life support, " Tanna said. 

Lindsey Theis at Newsy first reported this story.