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00:00Germs.
00:16Dear Tim and Moby,
00:18How do vaccines work?
00:20From Gregor.
00:22Hi Gregor.
00:24Vaccines trick your body into thinking it's been infected by a particular germ.
00:29Your immune system responds as though it's fighting an organism that could make you sick.
00:35You build up an immunity to the illness you're being vaccinated for, even though you've never
00:38actually had it.
00:41So if you ever do get infected with that germ, your body will be ready to fight back.
00:46Right, it's sort of like a training session for your body's defenses.
00:53In order to get exactly how vaccines work, you need to know a little bit about the immune
00:57system.
00:58The immune system is responsible for fighting illness and disease.
01:03Every day, bacteria and viruses invade your body.
01:09In most cases, these germs are stopped or killed by your body's first defenses, like
01:13the mucus in your nose, which traps organisms.
01:20Sometimes germs get past those defenses and make it into your bloodstream.
01:25White blood cells, or leukocytes, patrol your bloodstream looking for harmful invaders.
01:31If the leukocytes recognize a bad germ, they'll kill it before you get sick.
01:36But if for some reason they fail to notice a bad germ, it can multiply, invade your cells,
01:42and make you sick.
01:44No, no, well that's when white blood cells create antibodies to fight the infection.
01:52An antibody is a protein that binds with a specific molecule, or antigen, found only
01:57on the invading germ.
02:00The antibody is like a red flag.
02:02It signals leukocytes to kill the germ.
02:06Some antibodies can also neutralize germs on their own.
02:12After your immune system has stopped the infection, memory cells patrol your blood.
02:17They keep watch for that one specific antigen, usually for the rest of your life.
02:22Yep, that's why kids who get chickenpox almost never get it again.
02:28Their memory cells recognize the virus quickly the next time it shows up.
02:33This is called natural immunity.
02:35It happens as a result of your body successfully fighting off an illness.
02:41Vaccines give you immunity without the risks and discomfort of getting sick.
02:45They're composed of the antigens from a specific germ, which are introduced into your body
02:50to trigger an immune response.
02:52Your white blood cells react to those invaders as they normally would.
02:56They recognize the antigens and create antibodies for them.
03:01Well, vaccines only contain altered or weakened forms of germs, or none at all.
03:11That's why they don't make you sick.
03:14That's why many vaccinations need several doses to work.
03:18Since there's not enough of the germ to make you sick, your body's immune response may be very limited.
03:24Well, no one likes needles, but they're better than getting sick.
03:29And vaccines don't just protect individuals, they protect the whole population.
03:34When enough people in an area are vaccinated, they achieve something called herd immunity.
03:40That means a specific germ can't find anyone to infect.
03:46Herd immunity protects people who can't be vaccinated because their bodies are very sensitive,
03:50like babies and cancer patients.
03:53If we don't maintain our herd immunity, diseases can come back.
03:58Some places with low vaccination rates have already had measles outbreaks.
04:03Unless you live in one of those places, you've probably never met a young person who's had the measles,
04:08or polio, or smallpox.
04:12That's because vaccines have stopped these diseases from spreading.
04:17Doctors are still working on vaccines for many viruses, like HIV, the virus that leads to AIDS.
04:23And every year, a new flu vaccine has to be prepared.
04:27That's because the flu virus is constantly changing.
04:33I don't think you need those.
04:37After all, they don't work against computer viruses.