It's spring 2021, the Alpha variant of the coronavirus has spread rapidly, becoming the dominant variant worldwide.

時值 2021 年春天，新冠肺炎 Alpha 變異株已經快速擴散， 成為全球主要病毒株。

But another more transmissible variant is about to appear⏤Delta.

但是另一種更容易傳染的變異株即將出現，就是 Delta。

What happens when two variants clash?

當兩種變異株衝突時，會怎麼樣？

Let's do a thought experiment.

我們來做個思想實驗。

Suppose that the variants reach a hypothetical isolated city of 1 million people who are completely susceptible to both viruses on the same day.

假設這些變異株抵達一個完全孤立的假想城市，其中的一百萬名居民在同一天都可能被這兩種病毒感染。

When a person here is infected with Alpha, they transmit it to, on average, 5 close contacts,

當這裡的一個人感染到 Alpha，他平均傳染給 5 名親密接觸者，

then, begin to feel sick and immediately isolate themselves for the rest of the simulation.

然後他開始不舒服，馬上自我隔離到模擬結束。

The same thing happens with Delta, except that an infected person transmits it to, on average, 7.5 close contacts.

同樣的狀況也發生在 Delta，只不過於被感染的人平均傳染給 7.5 個親密接觸者。

What would you guess happens next?

你猜接下來會發生什麼事？

After six days, Alpha will have infected 15,625 people; Delta will have infected more than 10 times as many.

6 天後，會有 15,625 個人感染 Alpha、感染 Delta 的人數會超過十倍。

Just 20 hours later, Delta will have infected the rest of the population, all before Alpha could infect 6% of it.

僅僅 20 小時後，Delta 便會傳染給剩餘的人口，而這一切都發生在 Alpha 感染還不到 6% 人口之前。

With no one left to infect, Alpha dies out.

因為沒有剩下任何可以感染的人，Alpha 便滅絕了。

This model is drastically simplified, but it accurately reflects one thing that did happen in real life:

這個模型極度簡化，但它精確地反映出現實中確實發生的一個現象：

When both variants competed, Delta drove Alpha towards extinction in a matter of weeks.

當兩種變異株競爭時，Delta 只花了數週就讓 Alpha 滅絕。

Viruses are wildly successful organisms.

病毒是非常成功的生物。

There are about 100 million times as many virus particles on Earth as there are stars in the observable universe.

在地球上，病毒分子的數量是宇宙中可觀測星星數量的一億倍。

Even so, viruses can and do go extinct.

即便如此，病毒有可能，也的確會滅絕。

There are three main ways that can happen.

那要發生有三個主要途徑。

First, a virus could run out of hosts.

第一，病毒可能會耗盡宿主。

This might have happened in early 2020 to a flu lineage known as B/Yamagata.

這個狀況可能就是發生在 2020 年初的 B/Yamagata 流感病毒種系上。

When much of the world shut down, social-distanced, and wore masks to slow the spread of COVID-19,

當時全球許多地方都關閉、 保持社交距離、戴口罩以減緩新冠肺炎的散播，

that dramatically reduced the number of hosts available for B/Yamagata to infect.

那讓 B/Yamagata 能感染的宿主也大大地減少。

It'll take a few more flu seasons to know for sure if it's truly extinct or just hiding out in an animal reservoir.

這還需要再觀察幾個流感季節才能肯定它是否真正絕種，還是只是藏匿在動物宿主身上。

Many viruses, as part of their life cycle, cause diseases severe enough to kill their hosts.

許多病毒在生命週期中都會造成嚴重到足以讓宿主死亡的疾病。

This can be a problem because if a virus kills all its hosts, it could, in theory, run out of hosts to infect and go extinct.

這可能是個問題，因為如果病毒殺光了所有宿主，它理論上可能會耗盡可以感染的宿主而絕種。

This almost happened back in 1950s Australia.

這差點發生在 1950 年代的澳洲。

At the time, Australia was overrun by the European rabbit, an invasive species.

當時，澳洲被歐洲兔這種入侵物種佔領。

So, in an attempt to control the population, scientists released a virus called myxoma, which had been previously shown to be almost 100% lethal to European rabbits.

所以，為了試圖控制歐洲兔數量，科學家釋放了一種叫做黏液瘤的病毒，已知它對歐洲兔的致死率幾乎是 100%。

During the initial outbreak, as planned, tens, perhaps hundreds, of millions of European rabbits died.

在爆發初期時，如計畫一般，歐洲兔的死亡數達數千萬到數億。

But as the virus spread, it evolved a series of mutations that happened to make it less deadly, killing rabbits more slowly and killing fewer rabbits overall.

但隨這病毒散播，它演化出一系列的變異，恰好降低了致命性，較緩慢地誅殺兔子，且整體數量也較少。

With more infected hosts hopping around, this strain of the virus was more likely to spread than its deadlier cousin.

有更多被感染的宿主到處跳來跳去， 這種病毒株比它的致命表親更可能散播。

And, of course, rabbits evolved, too, to mount better immune responses.

當然了，兔子也開始演化以具備更好的免疫反應。

Overall, instead of killing every single rabbit, the virus evolved, the rabbit population bounced back, and both survived.

整題而言，病毒不是誅殺所有兔子，而是進行演化，兔子則數量回升，兩者共存。

The second way a virus could go extinct is if humans fight back with an effective vaccine and win.

可能會讓病毒絕種的第二種方式就是人類用有效的疫苗反擊並且獲勝。

Vaccination campaigns have driven two viruses essentially to extinction since vaccines were invented in the 1800s: smallpox and rinderpest, which kills cattle.

1800 年代疫苗發明之後，推行疫苗接種的活動就讓兩種病毒真的絕種了： 天花和會殺死牛的牛疫。

More on vaccination later.

疫苗接種議題稍後再聊。

The third way a virus can go extinct is if it's outcompeted by another virus or strain, like we saw earlier with Delta and Alpha.

會讓病毒絕種的第三種方式就是它被另一種病毒或病毒株打敗， 就如同先前 Delta 和 Alpha 的例子。

By the way, viruses don't always compete with each other.

順道一提，病毒不總是會彼此競爭。

A viral species can carve out its own distinct niche, for example, influenza infects your respiratory tract, and norovirus infects cells in your intestine, so both of these viruses can co-exist.

病毒物種能夠開拓出自己獨特的環境，例如流感病毒會感染你的呼吸道、諾羅病毒會感染你腸道內的細胞，所以兩種病毒可共存。

A virus' ecological niche can be tiny.

病毒的生態環境可能很小。

Hepatitis B and Hepatitis C viruses can infect the same cell; Hep B occupies the nucleus and Hep C occupies the cytoplasm.

B 型和 C 型肝炎病毒可以感染同一個細胞，B 肝佔領細胞核、C 肝佔領細胞質。

In fact, epidemiologists estimate that 2 to 10 percent of people with Hep C are also infected with Hep B.

事實上，流行病學家估計百分之 2 到 10 的 C 肝帶原者也感染到 B 肝。

So, will SARS-CoV-2, the species of virus that causes COVID-19, ever go extinct?

那麼，造成新冠肺炎的病毒物種 SARS-CoV-2 有可能絕種嗎？

Variants within the species will continue to arise.

這個物種中的變異株會持續出現。

Those variants might drive prior ones to extinction⏤or not.

那些變異株可能會讓舊的變異株絕種，或者不會。

Regardless of how the variants compete⏤or don't, the species itself, to which all the variants belong, is pretty firmly established among humans.

無論變異株如何競爭或是完全不競爭，所有變異株隸屬的物種已經穩穩地在人類之間立基。

If we managed to vaccinate enough people, could we drive SARS-CoV-2 to extinction?

如果我們能讓足夠的人接種疫苗，可能讓 SARS-CoV-2 絕種嗎？

Our vaccination campaign against smallpox worked because the vaccine was highly protective against infection, and smallpox had no close animal reservoir in which it could hide.

我們針對天花的疫苗接種活動奏效了，因為那種疫苗的保護力強到能讓接種者不被感染，而且天花病毒找不到接近的動物宿主讓它可以躲藏。

But SARS-CoV-2 can hide out in animals, and our current vaccines, while they provide excellent protection against severe illness and death, don't prevent all infections.

但 SARS-CoV-2 可藏匿在動物身上，而我們目前的疫苗雖然可以有效地避免重症和死亡，卻無法預防所有感染。

So, conceivably, there are two ways that SARS-CoV-2⏤the entire species⏤could go extinct.

所以 SARS-CoV-2 整個物種可能有兩種完全滅絕的方式。

A cataclysmic disaster could kill us all, or we could invent a universal vaccine that prevents all SARS-CoV-2 infections,

一場巨大災難可能屠殺全人類，或者我們可以發明一個能夠預防所有 SARS-CoV-2 感染的全面性疫苗，

those caused by all the variants that currently exist and those that don't.

包括由目前存在以及尚未浮現變異株所造成的所有感染。

Let's work toward that second option.

我們朝著第二個選項努力吧。

If a universal vaccine for COVID sounds appealing, what about a vaccine that protects you against everything?

如果新冠病毒的全面性疫苗聽起來很不錯，那麼有個可以讓你抵抗所有東西的疫苗如何呢？

Learn more about the pitfalls and promise of a universal vaccine with this video, or watch this video to learn about some older pandemic technology⏤plague masks.

透過這部影片學習全面性疫苗的隱憂和願景，或是觀看這部影片以了解一些更古老的防疫技術：瘟疫面具。