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How does community immunity work?

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Common Questions-child playing in playground

Germs can travel quickly from person to person.source: 1 And germs that cause infectious diseases can make people very sick.source: 1 Vaccines can help protect people from getting diseases.

Community immunity (also called “herd immunity”) happens when enough people in a community have immunity to a particular disease either through vaccination or prior infection.source: 1 It makes it much harder for that disease to spread.source: 1

The percentage of people who need to be immune for community immunity to work is different for each disease. But it can be as high as 95%.source: 2,source: 3 This is why it is so important for everyone who can be vaccinated to get vaccinated.

Vaccines do a very good job preventing disease but they are not perfect. If a disease is spreading in a community, some vaccinated people can still get sick.source: 4 Community immunity helps protect those who are vaccinated because it doesn’t let the disease spread easily. It also helps protect people who cannot get vaccines or for whom vaccines do not work as well.source: 1 This might be:source: 1,source: 5

  • Babies who are too young to get vaccines
  • Pregnant people, who can’t get certain vaccines
  • Older adults whose immune systems are not as strong
  • People who are allergic to vaccine ingredients
  • People with weakened immune systems, like people being treated for cancer

Key Evidence

  • Low vaccination rates prevent community immunity from working.source: 1 And they put children at a higher risk of getting sick from diseases. When you vaccinate your child, you help protect other children. Just as when other children are vaccinated, they help protect your child. For example, measles is extremely contagious.source: 6 Before the measles vaccine became available in 1963, measles caused 4 million cases and 450 deaths in the United States annually.source: 7 As more people got vaccinated against measles, the number of cases went down, and measles was considered eliminated in the United States in 2000.source: 8
  • Some diseases need community immunity all the time to help protect people from the disease. Measles is a good example here, too.source: 9 The number of people who need to be vaccinated for community immunity to work is high. More than 9 out of 10 people need to have immunity to control the spread of the disease.source: 2,source: 3
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Common Questions-adolescent girl with doctor

A Deeper Dive: How Vaccines Support Community Immunity

When your child gets vaccines, they aren’t the only ones who gain protection from dangerous diseases. Getting your child vaccinated can contribute to community immunity. By being up to date on vaccines, children not only help protect one another but also other children who cannot be vaccinated.

But for community immunity to work, most people in the community must be vaccinated.source: 3 The numbers are a little different for every disease, for example:

  • Diphtheria: 79–84% of the community needs to be vaccinatedsource: 10
  • Measles: 95% or greater of the community needs to be vaccinatedsource: 9,source: 11

Back to the common questions

More information

Still have questions? Talk to your child’s doctor, nurse, or pharmacist.

Sources

  1. HHS: Vaccines Protect Your Community
  2. JAMA: What Is Herd Immunity?
  3. CDC: Measles Cases and Outbreaks
  4. CDC: Explaining How Vaccines Work
  5. NIH: Community Immunity
  6. FDA: Vaccination Is the Best Protection Against Measles
  7. National Library of Medicine: Inpatient Morbidity and Mortality of Measles in the United States
  8. CDC: History of Measles
  9. CDC: Nearly 40 Million Children Are Dangerously Susceptible to Growing Measles Threat
  10. Human Vaccines & Immunotherapeutics: Evaluation of the establishment of herd immunity in the population by means of serological surveys and vaccination coverage
  11. WHO: History of the Measles Vaccine
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