What is ‘herd immunity,’ and how does it apply to COVID-19?

What is ‘herd immunity,’ and how does it apply to COVID-19?

While the world waits for a vaccine for the novel coronavirus, there are questions if the virus can be defeated another way.

Following the third straight day of more than 200 new COVID-19 cases in Allegheny County, the health department issued a new order for businesses that bans indoor dining and alcohol consumption. Customers are able to eat outside at restaurants with a three-drink limit, but groups are also limited to no more than 25 people inside.


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Other counties in western Pa. are expecting to see similar sanctions passed down to them by Gov. Tom Wolf due to the recent spike in coronavirus cases as well.

The term “herd immunity” has been used a lot by local and federal health officials when talking about the COVID-19 pandemic, but what exactly is it? And how does it apply to the coronavirus?

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Herd immunity happens when a large enough portion of a population becomes immune to an infectious disease. This is accomplished through either prior illness and recovery or vaccination.

According to research from Johns Hopkins University, if 80% of a population is immune to a virus, four out of every five people who come into contact with the disease won’t get sick -- and they won’t spread the disease further either.

Dr. David Dausey, professor of health science and provost of Duquesne University, told Channel 11 Allegheny County officials made the right move to close indoor dining and alcohol at bars as more of a targeted approach, since shutting more things down would come at a “greater cost.”

Dausey said herd immunity is possible, but a very high percentage of a population would need to be immune.

“It’s very doubtful that we’re close to herd immunity here in Allegheny County. Typically, to achieve herd immunity you need somewhere between 70 and 90 percent of the population to be immune from a disease,” Dausey said.

Dausey told Channel 11 that until there is a vaccine or enough people build up immunity to the coronavirus, we all should get used to wearing masks.

COVID-19 cases continue to rise across the country