a single vaccine that protects you against everything.

能保護你對抗一切的單一疫苗。

We'll get back to the grand vision later, but first, let's start with something that's being developed now:

我們等一下會提到這個雄偉的憧憬，但我們先從現在正研發的東西講起：

a vaccine that would protect you against every strain of the flu—even ones that don't exist yet.

一個可以保護你對抗任何流感病毒株的疫苗，包括還不存在的病毒株。

Here's one flu virus particle.

這是一粒流感病毒，

On the inside is the virus' RNA, and on the outside are lots and lots of hemagglutinin proteins.

裡面是病毒的 RNA，外面有許許多多血凝素蛋白質。

Hemagglutinin attaches to a receptor on a human cell and fuses the viral and human membranes, starting the infection.

血凝素附著於人體細胞的受體，融合病毒和人體的細胞膜開始發炎了。

Hemagglutinin is also one of the things your immune system recognizes and reacts to the most.

免疫系統會辨認血凝素，也會有所反應。

To understand how this works, think of hemagglutinin as a bust of 19th century French Emperor Napoleon Bonaparte.

為要了解作用機制，把血凝素想像成 19 世紀法國皇帝拿破崙的頭像。

Croissant!

可頌！

If you show Napoleon to an immune system and say, "remember him," the immune system will mostly focus on his head.

如果把拿破崙展示給免疫系統看，吩咐「記住他」，免疫系統主要會注意他的頭部。

And the same is true for the real hemagglutinin.

血凝素也是一樣。

One way the immune system remembers things is by physically interacting with them.

免疫系統記住東西的辦法之一就是和它們直接接觸。

Think of it as making plaster molds of parts of the head: we call these molds antibodies.

把它想像成塑造石膏頭像的模具：這些模具叫做抗體。

The antibodies float around your bloodstream for a while and then can diminish,

抗體在我們血液裡存在一陣子，然後可能會慢慢消失，

but blueprints on how to make them are stored in specialized memory cells, waiting for future Napoleons to invade.

但是製造的藍圖具有特別的記憶細胞，等待未來拿破崙的入侵。

Here's the thing, though.

可是有一點，

Hemagglutinin is constantly mutating.

血凝素一直在突變。

Most mutations are subtle, produced by single letter changes in the virus' RNA: like this or this.

多數的突變很細微，只變了病毒 RNA 的一個字母，像這個或那個。

Over time, Napoleon/hemagglutinin's head can change enough that our antibodies become less good at recognizing it.

過一段時間，拿破崙或血凝素的頭可能變得多到我們的抗體變得比較不會辨認了。

This is called antigenic drift.

這叫做抗原漂移。

Influenza is constantly drifting; that's one reason you have to get a new flu shot every year.

流感一直在漂移；這就是每年需要新流感疫苗的原因之一。

But sometimes bigger changes happen.

但有時候也會發生比較大的改變。

An animal, usually a pig, can get infected with, say, a human flu and a bird flu.

一個動物，通常是豬，可能會同時感染到，比方說，人類和鳥類的流感。

And those different viruses might infect the same cell.

這兩種病毒可能感染同一個細胞。

If that happens, the two different viral genomes can recombine in tens or even hundreds of ways.

如果這樣發生了，這兩個病毒的基因組可以有幾十甚至幾百種方法重組。

The human flu virus could pick up a bird flu hemagglutinin that's never infected humans before.

人類的流感病毒可以取得鳥類流感的血凝素，而這血凝素從未感染過人類。

This is called antigenic shift, and if you get infected by this version of influenza, none of the antibodies against Napoleon's head are going to help you.

這叫做抗原轉變，如果你感染到這種流感，沒有任何一個對付拿破崙頭像抗體幫得上忙。

Antigenically shifted viruses have the potential to infect many people very quickly, causing epidemics and sometimes pandemics.

抗原轉變的病毒有潛力可以快速感染許多人，造成大流行甚至疫情。

A truly universal flu vaccine would be able to protect against current flu strains and future drifted or shifted strains.

真正泛流感疫苗得要能保護目前流感病毒和未來經由抗原飄移或抗原轉變而來的病毒。

But how do we design a vaccine against a strain that doesn't exist yet?

但是我們如何設計疫苗對抗還不存在的病毒株？

We look to the past.

我們往回看。

There are key parts of hemagglutinin that haven't changed much over time and are probably critical to infect human cells;

有些血凝素的關鍵部位長久以來沒改變過，可能對感染人類非常重要，

these "conserved regions" could be promising targets for universal vaccines.

這些「保留區」可能是普遍流感疫苗有希望的標靶。

But there's a problem that's hindered classical vaccine production.

但是傳統疫苗生產有個問題。

Many conserved regions are in the neck, and it's tough to get the immune system to react to the neck.

許多保留區在（病毒的）頸部，而很難讓免疫系統對頸部起反應。

Also, because influenza-like viruses have been around for hundreds of millions of years, there may not be a single region that's common across all species and subtypes of influenza.

而且類似流感的病毒已經存在幾億年， 可能沒有所有病毒種類和次類別共同的保留區。

But there's promising science in development.

但是有一個有希望的科學正在開發中。

Remember this?

記得這個嗎？

This is a protein called ferritin; its normal purpose is to store and move iron.

這蛋白質叫做鐵蛋白，它正常的功用是儲藏和運送鐵。

But it's also the rough size and shape of a small virus.

但是它的大小形狀和小的病毒大致相同。

And if you attach viral proteins to it, like this, you'd have something that looks, to an immune system, like a virus—but would be completely harmless and very engineerable.

如果你在它上面附著病毒蛋白，像這樣，你就得到一個在免疫系統看來像病毒的東西，但是完全無害而且很容易加工製造。

Recently, scientists engineered a ferritin nanoparticle to present 8 identical copies of the neck region of an H1 flu virus.

最近，科學家製造了一顆鐵蛋白微粒，它的外表顯露出 8 幅和 H1 流感病毒頸部區域完全一樣的結構。

They vaccinated mice with the nanoparticle, then injected them with a lethal dose of a completely different subtype, H5N1.

他們用這微粒當疫苗給老鼠接種，然後給牠們注射會致命的劑量的完全不同次種類病毒，H5N1。

All the vaccinated mice lived; all the unvaccinated ones died.

所有接種過疫苗的老鼠存活； 所有沒接種疫苗的老鼠死了。

Going one step beyond that,

再往前進一步，

there may be conserved regions that we could take advantage of across different-but-related virus species—like SARS-CoV-2, MERS, and a few coronaviruses which cause some common colds.

我們或可利用保留區交叉不同但有關聯的病毒物種，像 SARS-CoV-2、MERS，還有一些造成感冒的冠狀病毒。

Over the past few decades, a different part of the immune system has come into clearer focus.

過去幾十年間， 免疫系統的另一部分變成關注焦點。

Instead of antibodies, this part of the immune system uses a vast array of T cells that kill, for example, cells that have been infected by a virus.

不同於抗體，免疫系統的這部分比方說，用許多 T 細胞去殺已經被病毒感染的細胞。

Vaccines that train this part of the immune system, in addition to the antibody response, could provide broader protection.

訓練免疫系統這部分的疫苗加上抗體的對抗可提供更廣泛的保護。

A universal flu vaccine would be a monumental achievement in public health.

泛流感疫苗會是公共衛生劃時代的成就。

A fully universal vaccine against all infectious disease is— for the moment—squarely in the realm of science fiction,

在目前可以保護所有傳染病的疫苗還只存在科幻小說裡，

partially because we have no idea how our immune system would react if we tried to train it against hundreds of different diseases at the same time. Probably not well.

部分由於我們不知道免疫系統會如何反應，訓練它同時對抗幾百種疾病，可能不太好。

But that doesn't mean it's impossible.

但這不意味著不可能。

Look at where medicine is today compared to where it was two centuries ago.

看看今日的醫學成就和兩百年前的相比，

Who knows what it'll look like in another 50 or 100 years—maybe some future groundbreaking technology will bring truly universal vaccines within our grasp.

誰知道再 50 或 100 年後是怎樣——也許未來一些破天荒的科技會使真正泛用疫苗在我們掌控中。