Bacteria and viruses are pathogens. Pathogens can make people sick.

Our bodies have immune systems. They protect us from bacteria and viruses. They make antibodies. These are special proteins. Proteins make up most of our bodies. Antibodies fight diseases.

Some diseases can pass from person to person. Sometimes, many people get sick all at once. This is called an outbreak.

People can be immune to diseases. This means they will not get sick.

Preventing an Outbreak

Herd immunity is when a community is protected from a disease. We can do this by making people immune. This means they do not get infected.

If enough people are immune, then an outbreak does not happen. The disease cannot spread as easily. People are 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. It makes antibodies more quickly. It fights the sickness better the second time. They are now resistant to the disease.

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 what humans and other animals are made of.

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.

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. One example is a disease called smallpox (variola). This disease is no longer a threat. Enough people received the vaccine so that everyone is protected.