Medical experts promised herd immunity would be the decisive blow ending the COVID-19 pandemic. But what percentage of the population would need to be inoculated before reaching the magical threshold?
The World Health Organization said last summer that between 60% to 70% would probably suffice. Dr. Anthony Fauci admittedly moved the goalposts several times on herd immunity, suggesting last December the United States may only reach the herd immunity threshold if 90% of the population received COVID-19 vaccination.
Now, some medical experts say herd immunity will never be achieved in America.
What are the details?
As of Wednesday, one-third of American adults were fully vaccinated, while more than 50% of American adults had received at least one COVID-19 vaccine shot, according to data from the Centers for Disease Control and Prevention. That is tremendous progress considering vaccinations began less than five months ago.
But doctors who spoke with USA Today said herd immunity is no longer on the horizon, citing Americans who are vaccine-hesitant.
Gregory Poland, director of the Mayo Clinic's Vaccine Research Group, claimed herd immunity is "off the table."
"[Herd immunity is] theoretically possible but we as a society have rejected that," Poland told USA Today. "There is no eradication at this point, it's off the table. The only thing we can talk about is control.
"What has surprised me most is the incomprehensible rejection of science even among otherwise intelligent people," Poland added. "I'm truly flabbergasted to be watching this on a grand scale."
Dr. William Schaffner, an infectious disease expert at the Vanderbilt University School of Medicine, agreed, citing "independent-thinking people" as those likely to drag out the pandemic.
"There are going to be places, rural Idaho, for example, where you have very independent-thinking people where there may be continuing spread, because you only get up to 25% of people vaccinated," Schaffner told USA Today. "I'm really concerned this virus is going to continue to smolder in rural areas."
Surveys increasingly show that a large swath of Americans are reluctant to get the vaccine. A recently Monmouth University poll, for example, discovered that 1 in 5 American adults won't get the vaccine. A Quinnipiac University poll similarly found that about one-quarter of American adults won't get vaccinated.
What has happened in Israel?
More than half of Israel's population has been vaccinated — USA Today reported that 62% of Israelis have been inoculated — and another significant portion tested positive for COVID-19.
The benefits of such high immunity are clear, according to Christina Ramirez, biostatistics professor at UCLA.
"As soon as vaccination rates hit 50%, you saw cases and deaths just start to plummet," Ramirez told USA Today.
Indeed, what is happening in Israel — whose government is quickly dropping COVID-related restrictions — provides the rest of the world with an indication of what COVID herd immunity looks like.
Eyal Leshem, a director at Israel's largest hospital, told the BBC herd immunity is the only explanation for the sharp decline in cases and deaths in Israel.
"There is a continuous decline despite returning to near normalcy," he said. "This tells us that even if a person is infected, most people they meet walking around won't be infected by them."