Depth 1 · 82 s

Practice without the illness

Name: Practice without the illness
Uploaded: 2026-11-07T00:09:48.408843Z
Duration: 82 s
Description: A vaccine lets your immune system learn a germ without getting ill. How that works, how it protects people who can't be vaccinated, and what vaccines have done, from smallpox to measles.

A vaccine lets your immune system learn a germ without getting ill. How that works, how it protects people who can't be vaccinated, and what vaccines have done, from smallpox to measles.

About this video

Your immune system has a memory: once it has beaten a germ, it can stop that germ much faster next time. Usually it learns this by getting ill first. A vaccine lets it learn without the illness, by showing it a harmless version of the germ: a killed or weakened germ, a piece of one, or instructions (called RNA or DNA) that tell your own cells to make that piece for a short while. Depending on the vaccine, the protection can last for years, decades or a lifetime.

Some people can't be vaccinated, such as very young babies, people who are seriously ill and people with certain allergies. When enough people around them are immune, a germ can't find enough people to spread to: community immunity, or herd immunity. How many is enough depends on how easily a germ spreads. One person with measles can infect up to 18 others who aren't protected, so the World Health Organization (WHO) says at least 95% of people need two doses of measles vaccine.

Smallpox spread from person to person and killed many. After a worldwide vaccination effort, the last natural case was in Somalia in 1977, and in 1980 WHO declared it gone: the only human disease ever wiped out. A study for WHO found vaccines have saved at least 154 million lives in the 50 years since 1974, most of them babies, and vaccines for children save over 4 million lives every year. Measles deaths fell from about 780,000 in 2000 to about 95,000 in 2024.

Most side effects are mild and short, like a sore arm for 2 or 3 days. A serious allergic reaction is rare, and staff are trained to treat one. A study of over 650,000 children in Denmark found no link between the MMR vaccine and autism. This video goes with the lesson How Vaccines Work in Health Level 1 on Knaph.

This video shows depth 1 of Vaccines.

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Transcript

0:00Your immune system remembers a germ once it has beaten it. Usually it learns by getting ill first. A vaccine lets it learn without the illness.
0:09A vaccine shows it a harmless version. A killed or weakened germ, a piece of one, or instructions for your cells to make that piece for a while.
0:20Some people can't be vaccinated, like very young babies. When enough people around them are immune, the germ has nowhere to go.
0:31How many is enough? One person with measles can infect up to eighteen others, so at least ninety five percent need two doses.
0:41Smallpox had its last natural case in 1977. In 1980 it was declared gone, the only human disease ever wiped out.
0:50Vaccines have saved at least 154 million lives in fifty years. Measles deaths fell from about 780,000 in 2000 to about 95,000 in 2024.
1:02Most side effects are mild, like a sore arm for a couple of days. A serious allergic reaction is rare. And large studies found no link with autism.
1:14Practice without the illness, and a germ with nowhere to go.