It was a success.

此法相當成功。

The eight-year-old was inoculated against the disease, and this became the first ever vaccine.

這名接受接種的八歲男童能抵禦天花，世界首個疫苗於焉問世。

But why did it work?

但這背後的原理為何？

To understand how vaccines function, we need to know how the immune system defends us against contagious diseases in the first place.

想知道疫苗原理，我們必須先瞭解我們的免疫系統是如何抵禦外來傳染疾病的。

When foreign microbes invade us, the immune system triggers a series of responses in an attempt to identify and remove them from our bodies.

當遭受外來病菌侵襲時，免疫系統會啟動一系列反應，試圖辨識並將這些病菌趕出體外。

The signs that this immune response is working are the coughing, sneezing, inflammation and fever we experience, which work to trap, deter and rid the body of threatening things, like bacteria.

免疫反應的徵兆包括我們經歷過的咳嗽打噴嚏、發炎及發燒，這都是為了將有害物質如細菌等包圍、遏止並趕出體外。

These innate immune responses also trigger our second line of defense, called adaptive immunity.

此天生的免疫反應也會誘發第二道防線，稱之為後天免疫。

Special cells called B cells and T cells are recruited to fight microbes, and also record information about them, creating a memory of what the invaders look like and how best to fight them.

特殊的 B 細胞及 T 細胞會被徵召來抵抗病菌並記錄下病原菌資訊，以存檔了解侵略者的外觀及最佳抵禦方式。

This know-how becomes handy if the same pathogen invades the body again.

下次再碰上同樣病原體時，這些實戰知識就能立即拿來使用。

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

但儘管免疫反應如此精巧還是有風險存在。

The body takes time to learn how to respond to pathogens and to build up these defenses.

因為身體需要花時間才能了解如何應對病菌及建立防禦措施。

And even then, if a body is too weak or young to fight back when it's invaded, it might face very serious risk if the pathogen is particularly severe.

即便如此，若在發育未臻成熟或體衰時得病就無法有效抵抗疾病，因此若碰上特別棘手的病菌時就可能面臨非常嚴重的危險。

But what if we could prepare the body's immune response, readying it before someone even got ill?

但要是能在第一次得病前就讓免疫系統做好對抗疾病的準備呢？

This is where vaccines come in.

這就是疫苗的由來

Using the same principles that the body uses to defend itself, scientists use vaccines to trigger the body's adaptive immune system without exposing humans to the full strength disease.

原理就跟身體的自我防禦一樣，在沒有讓人體暴露於完整病程中的情況下，科學家利用疫苗來誘發身體的後天免疫系統。

This has resulted in many vaccines, which each work uniquely, separated into many different types.

於是許多疫苗因此問世；這些疫苗可被分成多種類別，每個都有其獨特的作用方式。

First, we have live attenuated vaccines.

首先有活性減毒疫苗。

These are made of the pathogen itself but a much weaker and tamer version.

由已被削減致病性的活體病菌所製成。

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

另外還有非活性疫苗，此疫苗中的病原菌已全被殺死。

The weakening and inactivation in both types of vaccine ensures that pathogens don't develop into the full-blown disease.

此兩種疫苗中含有已被弱化或無活性病菌可確保該病原菌不會在人體內發展成真正的疾病。

But just like a disease, they trigger an immune response, teaching the body to recognize an attack by making a profile of pathogens in preparation.

但卻又能像疾病一樣誘發免疫反應，為目標病菌建立檔案，教導身體辨識該病菌的侵襲。

The downside is that live attenuated vaccines can be difficult to make, and because they're live and quite powerful, people with weaker immune systems can't have them, while inactive vaccines don't create long-lasting immunity.

活性減毒疫苗的缺點是難以製備，且因內含活性相當強大的病菌，免疫系統弱的人並不適合接種，而非活性疫苗的缺點則是無法產生長久的免疫效力。

Another type, the subunit vaccine, is only made from one part of the pathogen, called an antigen, the ingredient that actually triggers the immune response.

另一種疫苗類型是次單位疫苗；這種疫苗只含部分病原體稱之為抗原，也是真正誘發免疫反應的成分。

By even further isolating specific components of antigens, like proteins or polysaccharides, these vaccines can prompt specific responses.

而進一步分離出抗原中的特定成分，如蛋白質或多醣，這類型疫苗可立即促使特定反應。

Scientists are now building a whole new range of vaccines called DNA vaccines.

科學家現已著手建立新的疫苗系列，稱之為 DNA 疫苗。

For this variety, they isolate the very genes that make the specific antigens the body needs to trigger its immune response to specific pathogens.

為使身體對特定病菌產生免疫反應，他們分離出目標抗原的基因。

When injected into the human body, those genes instruct cells in the body to make the antigens.

而人體在接種後，疫苗內的基因會指示體內細胞製造抗原。

This causes a stronger immune response, and prepares the body for any future threats, and because the vaccine only includes specific genetic material, it doesn't contain any other ingredients from the rest of the pathogen that could develop into the disease and harm the patient.

這會引發更強大的免疫反應，讓身體準備好對抗任何潛在威脅。此類型疫苗僅由特定基因物質組成，因此不含病原菌其它可能致病並危害病人健康的物質。

If these vaccines become a success, we might be able to build more effective treatments for invasive pathogens in years to come.

若能研發成功，就可能在幾年內建立更有效的治療方法來對抗侵入性病菌的感染。

Just like Edward Jenner's amazing discovery spurred on modern medicine all those decades ago, continuing the development of vaccines might even allow us to treat diseases like HIV, malaria, or Ebola, one day.

正如簡納當年的驚人發現促成過去數十年的醫學進步，隨著疫苗技術的持續發展，也許有天也能找到治療愛滋病、瘧疾，或伊波拉的方法。