Xuan, who was quick to note that he is not a public health expert, said he and his team followed Gu’s predictions and arrived at 60%, a figure he acknowledges is an assumption.

“The idea would be we don’t know if 60% is true,” he said. However, if states that have reached this threshold see steep declines in covid cases, “then it’s the number to watch.”

What About the 60% Marker?

Throughout the pandemic, health experts have tended to set the magic number for herd immunity between 50% and 70% — with most, including Dr. Anthony Fauci, the head of the National Institute of Allergy and Infectious Diseases, leaning toward the higher end of the spectrum.

“I would say 75 to 85% would have to get vaccinated if you want to have that blanket of herd immunity,” he told NPR in December.

The experts we consulted were skeptical of the 60% figure, saying the mechanics of the Fundstrat analysis were relatively sound but oversimplified.

Ali Mokdad, chief strategy officer for population health at the University of Washington, said the level of immunity needed to reach this goal can vary due to several factors. “Nobody knows what is herd immunity for covid-19 because it’s a new virus,” he said.

That said, Mokdad described using 60% as “totally wrong.” Data from other communities around the world show covid outbreaks happening at or near that level of immunity, he said. Indeed, the city of Manaus in Brazil saw cases drop for several months, then surge despite three-fourths of their residents already having had the virus.

Josh Michaud, associate director for global health policy at KFF, described the 60% assumption as “off-base.”

And some said it wasn’t even the main point.

Dr. Jeff Engel, senior adviser for covid at the Council of State and Territorial Epidemiologists, said the question of herd immunity may not even be relevant because, regarding covid, we may never reach it. The novel virus may become endemic, he said, which means it will continue circulating like influenza or the common cold. For him, lowering deaths and hospitalizations is more important.