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What Is Herd Immunity?

I've heard that "herd immunity" is part of why getting kids vaccinated is important. But lately I see news about how herd immunity could be a risky way to try to deal with the COVID-19 pandemic. So is herd immunity a good thing or not?
– Corrine

Herd immunity is the idea that when many people are immune to a contagious infection, usually by getting a vaccine, it's harder for that infection to spread in a community. Vaccines teach the body to recognize and fight germs so we can't get sick from them in the future. This helps us become immune to infections. Otherwise, people become immune only after recovering from an infection that they caught from someone else. To achieve herd immunity this way, many people would get sick or even die in the process.

Why Is Herd Immunity Important?

Herd immunity (also called community immunity) protects people who are not immune to a disease, such as those who:

  • never had the disease
  • aren't able to get the vaccine
  • cannot become immune because they have a weak immune system

When about 7 or 8 out of 10 people are immune to an infection in a community, their whole community is usually protected — not just those who are immune. Diseases that are very contagious, like measles, might need almost everyone to be immune.

Why Are People Talking About Herd Immunity and COVID-19?

It has been suggested that people with a lower risk of severe COVID-19 infection be allowed to become immune by catching it.

But because COVID-19 is a new disease, most health experts don't yet know if herd immunity to coronavirus is possible, for a few reasons:

  • We don't know if or for how long people who have recovered from COVID-19 are protected from getting infected again.
  • Coronavirus is very contagious, so it's likely that millions of people would have to get infected to create herd immunity. Many of them could die while waiting for it to happen. Those who don't die could get very sick and have serious post-infection problems. We're still learning about the long-term effects of the illness, but it seems that young people can have these problems as well as older ones.
  • The coronavirus vaccines are still new. We don't yet know how long widespread vaccination will take.

So yes, herd immunity is a good thing, but it must happen safely. Until enough people get a coronavirus vaccine, health experts worldwide say that the best way to prevent its spread is to:

  • Wear a mask when out in public.
  • Keep a safe distance from people you don't live with.
  • Avoid large gatherings, especially ones held indoors.
  • Wash your hands well and often.
  • If sick, stay home and contact your doctor.