But what is herd immunity? Brian Labus, PhD, MPH, an infectious disease epidemiologist and public health professor at the University of Nevada, Las Vegas, explains that for COVID-19 it would mean the broader population is protected from widespread infection—but that's unlikely to happen anytime soon in the U.S.
"Herd immunity is the idea that there is a high enough level of immunity in a population that disease transmission cannot be sustained and an outbreak would quickly extinguish itself," says Dr. Labus. "If we reach it in the population, it would mean we have the coronavirus outbreak under control."
Dr. Labus explains that there are two ways to reach herd immunity: natural mass infection and vaccination. "The level of immunity needed in the population depends on how easily the disease spreads," says Dr. Labus. For example, the population of the United States has herd immunity to the measles (largely due to vaccination), which, because it's so highly contagious, means that at least 93 percent of the population is immune. For COVID-19, 60 to 65 percent of the population will likely need to be immune, says Dr. Labus.
During a recent conversation at a live-streamed Smithsonian Associates event, director of the National Institute of Allergy and Infectious Diseases, Anthony Fauci, MD, explains that the U.S. is nowhere near the point of herd immunity. "We are nowhere near herd immunity yet,” says Fauci. “The mean [COVID-19 infection rate] in the country is around 2 to 3 percent.”
Additionally, a September 2020 study from the University of Georgia used statistical modeling to examine what COVID-19 infection and death rates would be in the UK if it followed a herd-immunity approach. They found that a governmental response that lacks social distancing and self-isolation guidelines to be insufficient. "Attempting to achieve herd immunity while simultaneously mitigating the impact of COVID-19 on hospital burden is an extremely challenging task," the study authors write.
"Immunity to a disease is achived through the presence of antibodies to that disease in a person’s system," explains the Centers for Disease Control and Prevention. "Antibodies are proteins produced by the body to neutralize or destroy toxins or disease-carrying organisms." Once a person immune to a disease (either by infection with the disease itself or through vaccination), the human body recognizes it when exposed to it and produces the antibodies needed to fight it.
Antibody tests have been touted as a means to determine who has already been infected and therefore potentially immune to COVID-19. But, some antibody tests are better than others, and recent cases have shown that COVID-19 reinfection is possible.
"We don't know if immunity to COVID-19 is temporary or long-lasting," says Dr. Labus. "If people lose immunity within a few months of infection, it would be difficult to ever reach [herd immunity]."
Before vaccines became widely available, it was difficult if not impossible to achieve high levels of immunity for infectious diseases. "Diseases would never really disappear and would cause outbreaks every few years," says Dr. Labus. "Unfortunately, the only way to reach the needed levels of immunity right now is through natural infection. If over 60 percent of our population becomes infected, we will have many people die from this disease before the outbreak is over."
And even if we are able to reach herd immunity for COVID-19, that doesn't mean that the disease will cease to exist.
"It is a common misconception that herd immunity will prevent disease altogether," says Dr. Labus. "Even if there is herd immunity, individual people will become sick, and there could be an outbreak among a subset of the population—people who aren't immunized, for example."
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