Herd immunity: What it means for you

Edgar Sanchez, MD, Orlando Health Medical Group Infectious Disease


People are hearing quite a bit about “herd immunity” these days, particularly as a potential solution to the COVID-19 crisis. But that will not occur quickly or easily.

“Herd immunity is going to happen with this virus at some point,” said Edgar Sanchez, MD, with the Orlando Health Medical Group Infectious Disease. “If we reach herd immunity without a vaccine, however, millions of people will die from this virus in America.”

What is herd immunity?

Herd immunity, or community immunity, refers to having enough people in a location with immunity to a disease threat, either through having survived the infection and developing an ability to fight it or through vaccination. Fewer people to infect makes a disease harder to spread and ends an epidemic. Herd immunity protects vulnerable people who cannot receive a vaccination, such as newborns or adults with weak immune systems.

Veterinarians George Potter and Adolph Eichhorn coined the term herd immunity in an article published in 1916 in the Journal of the American Veterinary Medical Association. They suggested retaining rather than killing cows immune to a cattle disease to slow down an outbreak and not adding new cows to the herd. New cows would give the disease more cattle to infect.

Scientists continued to study herd immunity in animal and human diseases. During the 1950s and 1960s, as vaccines were developed, scientists tried to determine how many people would need to receive a vaccine to create herd immunity. It remains an interesting question.

Currently, experts have not come to a consensus about what percentage of people with immunity to COVID-19 would be required to protect others through herd immunity.

Dr. Sanchez suggested 65 percent or 70 percent of the population would need to be immune to COVID-19 for herd immunity to happen. About nine percent of Floridians have had COVID-19.

“We have a long way to go and a lot of deaths if we are going to reach herd immunity that way,” Dr. Sanchez added.

Some experts have suggested using natural infection to develop herd immunity is unethical and unachievable.

Why will herd immunity will be difficult to achieve?

For herd immunity to be successful, a significant number of people in a community must be immune to the disease. Herd immunity works. It was a key element in eradicating smallpox.

But a recent study from the University of Georgia in Athens found herd immunity an impractical strategy for fighting COVID-19.

By one estimate, in the United States, to achieve herd immunity without a vaccine, 213 million people would need to be infected with COVID-19, 2.3 million would be hospitalized, and about 1.4 million would die. Those numbers assume someone with COVID-19 could not become reinfected with the virus. However, cases of reinfection have been reported.

Another estimate suggests 197 million cases and 2.95 million deaths could achieve herd immunity in this country. With either model, the loss of life seems unacceptable. Additionally, it would overwhelm hospitals.

Dr. Sanchez acknowledged these numbers of deaths to reach herd immunity without a vaccine are unrealistic.

“Two-hundred thousand deaths, what we have now [from COVID-19], is too much,” Dr. Sanchez said. “We don’t want anymore, especially since it’s something that can be mitigated with wearing masks and not congregating.”

Additionally, COVID-19 has disproportionately affected people of color, Blacks and Hispanics.

“More people die from that disease from those communities and suffer complications,” Dr. Sanchez added. “We see this in the literature and in practice.”

Another potential complication to achieving herd immunity is that people who have survived COVID-19 likely do not have lasting immunity, as is true with other coronaviruses such as the common cold. Some research suggests immunity may last only two to three months.

Vaccinations could help

Vaccines are in development. When a safe and effective vaccine for COVID-19 becomes available, and many people accept the vaccine, herd immunity will become possible.

Yet many people do not trust vaccines, complicating the ability to achieve herd immunity. Dr. Sanchez encourages people to review the data from the vaccine trials, when available.

Last month, a survey by the Pew Research Center found that only 51 percent of U.S. adults and 32 percent of Black Americans would definitely or probably get a COVID-19 vaccine if one were available.

Until herd immunity exists, social measures, such as physical distancing, wearing masks, frequent hand washing, and avoiding crowded places, remain the best method of preventing a COVID-19 infection.

“We have seen dramatic decreases in the amount of people getting sick with [COVID-19] when the majority of people wear masks,” Dr. Sanchez said. “We want people to wear masks, [practice] social distancing, not be in large groups, and be outdoors if you have to be in a large group. All of those interventions we can do decrease the risk, even a little bit, but all of those things together can decrease the risk a lot.”

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