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Health News Florida

Herd Immunity For Coronavirus A Long Way Off, Health Experts Say

illustration of herd immunity
Centers For Disease Control and Prevention
Herd immunity happens when a majority of the population becomes immune to a disease, either by getting sick and recovering or through a vaccine.

As cases of the coronavirus surge across Florida, some suggest herd immunity could be a solution.    

It's the idea of fighting a disease by making a majority of the population immune, and it is often cited as the reason why vaccines are so effective in controlling deadly diseases like polio and the measles. 

But there's no vaccine for the coronavirus now and widespread distribution of one is even further off. That means herd immunity would require between 60% and 80% of the population to get sick and recover from COVID-19 over a short period of time, health experts said.

That would be catastrophic for the health care system, said Dr. Jason Wilson, an emergency medicine specialist at Tampa General Hospital.

“If we're going to start to reach those numbers of diagnosed cases out there, we would be completely overrun,” Wilson said during a recent gathering of Cafe Con Tampa.

Herd immunity happens when a majority of the population becomes immune to a disease -- either by getting sick and recovering or through a vaccine. When enough of the population is immune to a disease, there’s nowhere for it to spread.

But health experts say there's still a long way to go before coronavirus could be contained in this way.

And getting there without a vaccine would be dangerous. Even if only 15% to 20% of the population got sick, it would overwhelm the health care system, Wilson said. 

“We would hit that line of where you start to see ICU admissions and then when you start to see that get overrun, that's when that case fatality rate starts to jump,” he said.  

Wilson pointed to the math to illustrate his point.

More than 150,000 people in Florida have tested positive for the coronavirus since March. Wilson suggested multiplying that by 10 to account for people who got the virus but didn't get tested. Still, that’s only about 7 percent of the state's 21.5 million residents.

To reach 60% of the state’s population – the estimated lowest threshold for herd immunity -- at least 13 million people in Florida would have to recover from COVID-19.  

“So what that would get us is a lot of death along the way,” Wilson said.

And there's another problem. Unlike the measles or chicken pox, where recovery comes with lifetime immunity, it’s not clear how long immunity lasts for someone who survives COVID-19.

It may only last about two months, said Dr. Kartik Cherabuddi, an infectious disease specialist at the University of Florida.

“Even if you've had the disease, say two-and-a-half months ago, you could be susceptible to it again,” Cherabuddi said. “So when we are trying to drive toward herd immunity, if we don't have long lasting protection, that doesn't help.”

He says a vaccine could provide longer immunity.

But even with a vaccine, Cherabuddi said more steps will be needed to keep outbreaks from happening.

He describes four things that have to happen in unison: a vaccine; a medication to prevent people from getting sicker; protecting the elderly and vulnerable people -- like those with chronic conditions; and controlling the spread through masks, quarantine and contact tracing.

“These are processes that have to happen in parallel until we get to that high herd immunity with the vaccine and maybe a combination of infections,” Cherabuddi said.

The bottom line, he said, is herd immunity won't be achieved any time soon. So the best thing to do at this stage, is continue practicing social distancing and wear a mask.
