0:00:07.090,0:00:10.441
In 1796, a scientist, Edward Jenner,[br]

0:00:10.441,0:00:15.111
injected material from a cowpox virus[br]into an eight-year-old boy

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with a hunch that this would provide[br]the protection needed

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to save people from deadly outbreaks[br]of the related smallpox virus.

0:00:23.243,0:00:24.890
It was a success.

0:00:24.890,0:00:27.619
The eight-year-old was inoculated [br]against the disease

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and this became the first ever vaccine.

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But why did it work?

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To understand how vaccines function,

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we need to know how the immune system[br]defends us against contagious diseases

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in the first place.

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When foreign microbes invade us,

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the immune system triggers[br]a series of responses

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in an attempt to identify [br]and remove them from our bodies.

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The signs that this immune [br]response is working

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are the coughing, sneezing,[br]inflammation and fever we experience,

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which work to trap, deter and rid the body[br]of threatening things, like bacteria.

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These innate immune responses[br]also trigger our second line of defense,

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called adaptive immunity.

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Special cells called b-cells and t-cells[br]are recruited to fight microbes,

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and also record information about them,

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creating a memory of what [br]the invaders look like,

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and how best to fight them.

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This know-how becomes handy

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if the same pathogen [br]invades the body again.

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But despite this smart response,[br]there's still a risk involved.

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The body takes time to learn[br]how to respond to pathogens

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and to build up these defenses.

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And even then,

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if a body is too weak or young[br]to fight back when its invaded,

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it might face very serious risk[br]if the pathogen is particularly severe.

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But what if we could prepare[br]the body's immune response,

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readying it before someone even got ill?

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This is where vaccines come in.

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Using the same principles[br]that the body uses to defend itself,

0:02:00.998,0:02:05.975
scientists use vaccines to trigger[br]the body's adaptive immune system,

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without exposing humans[br]to the full strength disease.

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This has resulted in many vaccines,[br]which each work uniquely,

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separated into many different types.

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First, we have live attenuated vaccines.

0:02:19.769,0:02:24.748
These are made of the pathogen itself,[br]but a much weaker and tamer version.

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Next, we have inactive vaccines,[br]in which the pathogens have been killed.

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The weakening and inactivation[br]in both types of vaccine

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ensures that pathogens don't develop[br]into the full blown disease.

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But just like a disease,[br]they trigger an immune response,

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teaching the body to recognize an attack

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by making a profile [br]of pathogens in preparation.

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The downside is that live attenuated [br]vaccines can be difficult to make,

0:02:51.049,0:02:53.249
and because they're live [br]and quite powerful,

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people with weaker immune systems[br]can't have them,

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while inactive vaccines[br]don't create long lasting immunity.

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Another type, the subunit vaccine,

0:03:03.790,0:03:08.033
is only made from one part [br]of the pathogen, called an antigen,

0:03:08.033,0:03:11.569
the ingredient that actually triggers [br]the immune response.

0:03:11.569,0:03:14.946
By even further isolating[br]specific components of antigens,

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like proteins or polysaccharides,

0:03:17.383,0:03:21.753
these vaccines can prompt [br]specific responses.

0:03:21.753,0:03:25.671
Scientists are now building [br]a whole new range of vaccines

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called DNA vaccines.

0:03:27.171,0:03:32.029
For this variety, they isolate the very [br]genes that make the specific antigens

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the body needs to trigger its immune [br]response to specific pathogens.

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When injected into the human body,[br]

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those genes instruct cells [br]in the body to make the antigens.

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This causes a stronger immune response,

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and prepares the body [br]for any future threats,

0:03:47.912,0:03:51.382
and because the vaccine only includes[br]specific genetic material,

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it doesn't contain any other ingredients[br]from the rest of the pathogen

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that could develop into the disease[br]and harm the patient.

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If these vaccines become a success,

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we might be able to build [br]more effective treatments

0:04:03.515,0:04:06.152
for invasive pathogens in years to come.

0:04:06.152,0:04:08.370
Just like Edward Jenner's [br]amazing discovery

0:04:08.370,0:04:11.656
spurred on modern medicine [br]all those decades ago,

0:04:11.656,0:04:13.685
continuing the development of vaccines

0:04:13.685,0:04:16.895
might even allow us [br]to treat diseases like HIV,

0:04:16.895,0:04:17.787
malaria,

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or ebola, one day.