Skip To Main Content
Main Content

What Is Herd Immunity?

April 08, 2021

If you have heard about herd immunity, you may be wondering what it is and how it can help in the fight against COVID-19. Herd immunity occurs when a large proportion of a population is immune to an infectious disease, making it more difficult for that disease to spread from person to person. Herd immunity can be achieved by either natural infection or, ideally, by vaccination.

Herd immunity against COVID-19

To safely achieve herd immunity against COVID-19, experts recommend a substantial proportion of the population will need to be vaccinated.1 By vaccinating against COVID-19, you can help prevent additional illnesses and deaths, and lower the rate of transmission.

Once enough people are vaccinated, infection rates will begin to decline because there will be fewer unprotected people for the virus to infect. The percentage of people that need to be vaccinated for this to occur is called the herd immunity threshold.

The herd immunity threshold for COVID-19 is currently unknown. Thresholds can vary from one disease to the next based on how contagious it is. For example, the threshold for measles is 95%, while the threshold for polio is 80%.1 Since COVID-19 is highly contagious, it's estimated that to achieve herd immunity, a significant percentage of the population will need to be vaccinated.

Returning to "normal"

Being vaccinated will help keep you, your family, and your community healthy and safe. Once the rate of infection begins to decline, we may be able to ease up on preventive measures and engage in school, work, and social activities as we did before the pandemic began. The quickest way to reach herd immunity is for all Americans to receive the vaccine as soon as it's available to them.

Continued care and resources

As vaccinations continue across the country, it's recommended that everyone continue taking preventive measures such as social distancing, wearing a mask, and washing your hands frequently to prevent possible infections until herd immunity is achieved.2 If you think you may have COVID-19, you can search for a testing location near you. You can also read about the different types of COVID-19 testing available.

For updates and information on COVID-19, the vaccines, and caring for your well-being during the pandemic, visit

1 World Health Organization website; Coronavirus disease (COVID-19): Herd immunity, lockdowns and COVID-19 (December 2020);
2 Centers for Disease Control and Prevention website; Frequently Asked Questions about COVID-19 Vaccination (January 2021);