Herd Immunity: Strength in Numbers

Herd Immunity: Strength in Numbers

Herd immunity is the idea that an entire community can be protected from an illness by immunizing a certain percentage of individuals.


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Biology, Genetics, Health

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Bacteria and viruses are pathogens that can make people sick. Our bodies have immune systems that protect us from bacteria and viruses. The immune system makes antibodies. Antibodies are special proteins. They fight diseases.

Some diseases can be passed from person to person. If many people get sick, it can lead to an outbreak. An outbreak is when many people get sick all at once. It usually happens in a certain place.

People can be immune to diseases. When a person is immune, it means that the person will not get sick. They are resistant to the disease. If enough people are immune, then an outbreak does not happen. Eventually, the disease might disappear.

Immunization Is Best

Herd immunity is one way that a whole community can be protected from an illness. We can do this by making some people immune to a disease. This means they do not get infected. When many people are immune to a disease, then it cannot spread as easily. This helps keep everybody safer.

There are two ways that people can become immune. The first way is when someone gets sick. Say a bacteria or virus attacks a person. Then, the immune system makes antibodies. These are proteins that fight the disease. Antibodies help a person recover.

Say the same bacteria or virus attacks a person again. This time, the person's body recognizes it, and it makes antibodies more quickly. It fights the sickness better the second time.

Another way that people can become immune is through a vaccine. This is a shot you get from a doctor. It contains a weak version of a bacteria or virus or mRNA made from them. mRNA reads DNA to help make proteins. Proteins are the building materials for animals, like humans.

Vaccines make the body immune. This means you are less likely to get sick if you come across the bacteria or virus in the real world.

Vaccines Produce Antibodies

Edward Jenner was an English scientist. He lived in the 1700s. During that time, smallpox (variola) was a deadly disease. At the time, people in China, India, and West Africa would take pathogens from a person who had smallpox and wiped it into the arm of someone who didn't have the disease. It helped the person without smallpox fight against the disease. This is how immunization works. But sometimes, fighting the disease that way, would kill the person.

So Jenner thought of another way. Another common disease was cowpox. It was similar to smallpox, but it was milder. Jenner saw that people who had been infected with cowpox did not catch smallpox. Jenner thought that the two diseases were related. He guessed that catching cowpox would immunize a person against smallpox.

Jenner tested this theory. He took pathogens from a person who had cowpox. He wiped them into a cut on a boy's arm. The boy got sick but soon got better. Jenner then put the smallpox virus into the boy. The boy did not get sick. Cowpox pathogens made him immune to smallpox.

Today, there are vaccines. When people receive a vaccine, their immune system then knows how to produce antibodies. It knows how to fight the disease in the future. That way, these people are immune. They are less likely get sick if they come across the pathogen in the real world.

Making It Work

For herd immunity to work, a certain number of people have to be immunized. This number is different for every disease.

If enough people are immune, then outbreaks can be stopped. The disease does not spread as easily. One example is a disease called smallpox. This disease is no longer a threat. Enough people received the vaccine so that everyone was protected from smallpox.

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Tyson Brown, National Geographic Society
National Geographic Society
Production Managers
Gina Borgia, National Geographic Society
Jeanna Sullivan, National Geographic Society
Program Specialists
Sarah Appleton, National Geographic Society, National Geographic Society
Margot Willis, National Geographic Society
Last Updated

October 19, 2023

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