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How big is the herd?

How many people must be vaccinated to keep COVID-19 at bay?

Article Author: Katie McPherson

Article Date:

graphic image depicting a percentage sign made up of lots of people

As frontline health care workers across the United States receive the first doses of the coronavirus vaccine, the public eagerly awaits information about when it will be available to the masses. In the meantime, many are wondering just how many people need to be vaccinated in order to achieve herd immunity, which could be the light at the end of this pandemic tunnel.

What is herd immunity?

Herd immunity happens when enough people in a certain population have become immune to an illness — either because they’ve already been infected, or in the majority of cases, because they've been vaccinated — to protect those without immunity. Vincy Samuel, PhD, MPH, director of Employee Health at Baptist Health, said the number of vaccinated people it takes to reach herd immunity depends on the virus in question.

“The more contagious the disease, the higher the percentage of the population that needs to be immune to achieve herd immunity. The percentage for herd immunity from measles, for example, is really high, around 94%,” she explained.

Achieving herd immunity as a nation would mean those who can receive the vaccine are helping to protect those who can’t from getting COVID-19.

“There’s not yet a vaccine for children under 16. There may also be people who are allergic to a component of the vaccine, in which case they may not be eligible to receive it,” Samuel said.

How big is the herd?

What is that magic herd immunity percentage for the COVID vaccine? Experts are not yet sure. Some sources state anywhere from 70% to 90% of the U.S. population will need to receive both doses in order to reach herd immunity, as we have for measles, mumps, and other illnesses.

“Besides just needing a large percentage of immunity before herd immunity can be achieved, we also don’t know how long immunity lasts,” Samuel said. “We still have much to learn about both natural and vaccine-induced immunity to COVID-19. In addition, you may still have outbreaks in areas with low vaccination rates.”

Samuel added the most important things anyone can do to help end the pandemic are:

  1. Get vaccinated
  2. Receive both doses of the vaccine in the recommended timeframe
  3. Continue practicing social distancing, masking, handwashing, and other precautions until herd immunity is achieved

Remember, you can still transmit the virus to those who are susceptible even after you are vaccinated, Samuel cautioned.


For more information about COVID-19, visit baptistjax.com/covid19. To learn more about the COVID-19 vaccine or find answers to frequently asked questions, visit baptistjax.com/covid19vaccine.

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