How Vaccines Train the Immune System

0:00How can a vaccine protect you from a disease you have never had?

0:04Germs are micro-organisms that cause disease. Each kind has its own surface shapes, called antigens.

0:13Your body's defence against germs, the immune system, uses white blood cells.

0:19Some white blood cells make antibodies, proteins that lock onto the germ's antigens so it can be destroyed.

0:26A vaccine shows your immune system a harmless version of a germ. Common kinds use a weakened or killed germ, one piece of it, or mRNA instructions.

0:38mRNA, or messenger RNA, is a set of instructions: your cells read it and make one piece of the germ.

0:47It never enters the nucleus, where your DNA is kept, so it cannot change your DNA. Your cells soon break it down.

0:56Now follow the level of antibodies in your blood over time.

1:00After the vaccine, antibodies rise slowly and only a little. The vaccine is harmless, so a slow start does not matter.

1:09Some white blood cells become memory cells, which remember the antigens, often for many years.

1:16Later, if the real germ gets in, memory cells recognize its antigens straight away.

1:23Now antibodies come much faster and in far greater numbers, so the germ is usually destroyed before you get ill.

1:31Worldwide vaccination ended smallpox: it was declared eradicated in 1980, so it no longer spreads anywhere.

1:40A vaccine safely trains your immune system, so memory cells can fight the real germ fast.