How Do Vaccines Work?

Step 1 of 5

Your immune system learns from experience.

The first time it meets a germ it takes days to work out a response. Meanwhile you are ill. It keeps a record afterwards.

Step 2 of 5

A vaccine supplies the experience safely.

It shows the immune system a recognisable piece of the germ — inactivated, weakened, or just a protein — with no ability to cause the disease.

Step 3 of 5

The body builds antibodies and memory cells.

It makes antibodies that lock onto that specific shape, and memory cells that persist for years holding the instructions.

Step 4 of 5

The real infection then loses the race.

A germ needs time to multiply. A prepared immune system attacks immediately and usually wins before you notice anything.

Step 5 of 5

Enough vaccinated people protect the rest.

If a germ cannot find enough susceptible people, chains of transmission break. That protects those who cannot be vaccinated themselves.

Smallpox killed hundreds of millions and was eradicated entirely by vaccination. It is the only human disease that has been.