For a term that's at least 100 years old, "herd immunity" has gained new life in 2020.
It starred in many headlines last month, when reports surfaced that a member of the White House Coronavirus Task Force and adviser to the president, Dr. Scott Atlas, recommended it as a strategy to combat COVID-19. The Washington Post reported that Atlas, a health care policy expert from the Hoover Institution of Stanford University, suggested the virus should be allowed to spread through the population so people build up immunity, rather than trying to contain it through shutdown measures.
At a town hall event a few weeks later, President Donald Trump raised the idea himself, saying the coronavirus would simply "go away," as people developed "herd mentality" - a slip-up that nonetheless was understood to reference the same concept.
And as recently as last week, Sen. Rand Paul, R-Ky., sparked a heated debate at a committee hearing when he suggested that the decline in COVID-19 cases in New York City was due to herd or community immunity in the population rather than public health measures, such as wearing masks and social distancing. Dr. Anthony Fauci, the top U.S. infectious disease official, rebuked Paul, pointing out that only 22% of the city's residents have COVID-19 antibodies.
"If you believe 22% is herd immunity, I believe you're alone in that," Fauci told the senator.
All this talk got us thinking: People seem pretty confused about herd immunity. What exactly does it mean and can it be used to combat COVID-19?
AN UNCERTAIN STRATEGY WITH GREAT COST
Herd immunity, also called community or population immunity, refers to the point at which enough people are sufficiently resistant to a disease that an infectious agent is unlikely to spread from person to person. As a result, the whole community - including those who don't have immunity - becomes protected.
People generally gain immunity in one of two ways: vaccination or infection. For most diseases in recent history - from smallpox and polio to diphtheria and rubella - vaccines have been the route to herd immunity. For the most highly contagious diseases, like measles, about 94% of the population needs to be immunized to achieve that level of protection. For COVID-19, scientists estimate the percentage falls between 50% and 70%.
Before the COVID-19 pandemic, experts can't recall examples in which governments intentionally turned to natural infection to achieve herd immunity. Generally, such a strategy could lead to widespread illness and death, said Dr. Carlos del Rio, an expert in infectious disease and vaccines at the Emory University School of Medicine.