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Dr. Fauci: How We'll Know When We've Reached Herd Immunity With Covid

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Since the start of the pandemic, many people have anticipated "herd immunity" against Covid as an elusive finish line. The catch is, no one even knows for certain what the threshold of herd immunity for Covid-19 is, Dr. Anthony Fauci, White House chief medical advisor, told YouTube's Dr. Mike Varshavski during an interview published June 6.

So how will we know if and when we're there?

"When you get that level of protection that turns out to be the threshold of herd immunity, you'll know it, because you'll see the infections almost disappear," Fauci told Varshavski.

Even if Covid doesn't disappear entirely, infections likely won't be as severe or lead to hospitalization and death, because enough people are vaccinated.

But herd immunity could also vary depending on where you live. In communities where vaccine acceptance rates are low, there's more potential for outbreaks. Currently vaccination rates are lower in the South, for instance, while places such as New York and California already have more than 70% of the adult population with at least one dose.

Estimates based on measles and other diseases suggest that herd immunity occurs when 70%-80% of the population is vaccinated. But Fauci has said that the usual definition of "herd immunity" doesn't apply to the Covid pandemic.

"Forget this issue of herd immunity and just get as many people vaccinated as you possibly can, as quickly as you possibly can" to slow transmission of the virus, he told The New York Times' Apoorva Mandavilli on "The Daily" May 7.

In fact, with more contagious variants spreading and vaccine distribution stalling in parts of the country, some experts say it's unlikely that the United States will ever reach herd immunity.

But "[Covid-19] certainly will go to a level that would no longer be a public health hazard, as it were, in this country," Fauci told Varshavski.

Currently, 44% of the total population is fully vaccinated against Covid, according to the Centers for Disease Control and Prevention. In May, President Joe Biden set a goal of vaccinating 70% of American adults by July 4.

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