It’s spring 2021. The Alpha variant of the coronavirus has spread rapidly, becoming the dominant variant worldwide. But another, more transmissible variant is about to appear— Delta. What happens when two variants clash?
時值 2021 年春天。 新冠肺炎病毒的 Alpha 變異株已經快速擴散, 變成全世界的主流病毒株。 但,另一種更容易傳染的 變異株即將出現——Delta。 當兩種變異株碰撞時,會怎麼樣?
Let’s do a thought experiment. Suppose that the variants reach a hypothetical isolated city of 1 million people who are completely susceptible to both viruses on the same day. When a person here is infected with Alpha, they transmit it to, on average, 5 close contacts, then begin to feel sick and immediately isolate themselves for the rest of the simulation. The same thing happens with Delta, except that an infected person transmits it to, on average, 7.5 close contacts.
咱們來做個思想實驗。 倘若這些變異株到了 一個完全孤立的假想城市, 城市內有一百萬居民,全部 都很容易感染這兩種病毒, 兩種病毒同一天到。 當這裡的一個人感染到 Alpha, 平均就會傳染給 5 名親密接觸者, 接著,他開始不舒服, 便馬上自我隔離一直到模擬結束。 Delta 的狀況也一樣, 差別只在於被感染的人平均會 傳染給 7.5 個親密接觸者。
What would you guess happens next?
你猜接下來會如何?
After six days, Alpha will have infected 15,625 people. Delta will have infected more than 10 times as many. Just 20 hours later, Delta will have infected the rest of the population— all before Alpha could infect 6% of it. With no one left to infect, Alpha dies out.
6 天後, 會有 15625 個人感染 Alpha。 感染 Delta 的人數會超過十倍。 光是 20 小時後, 剩下的人都會感染到 Delta, 此時感染 Alpha 的人數 都還沒到總人口的 6%。 沒有剩下任何人可以感染了, Alpha 便滅絕了。
This model is drastically simplified, but it accurately reflects one thing that did happen in real life: when both variants competed, Delta drove Alpha towards extinction in a matter of weeks.
這個模型極度簡化, 但它確實能精確反映出 現實中發生的一個現象: 當兩種變異株競爭時, Delta 只花了幾個星期 就讓 Alpha 絕種。
Viruses are wildly successful organisms. There are about 100 million times as many virus particles on Earth as there are stars in the observable universe. Even so, viruses can and do go extinct.
病毒是非常成功的生物。 在地球上,病毒顆粒的數目是宇宙中 可觀察到的星星的數目乘以一億倍。 就算如此,病毒仍然 有可能/確實會絕種。
There are three main ways that can happen.
主要有三種方式,會讓病毒絕種:
First, a virus could run out of hosts.
第一,病毒可能會用光宿主。
This might have happened in early 2020 to a flu lineage known as B/Yamagata. When much of the world shut down, social distanced, and wore masks to slow the spread of COVID 19, that dramatically reduced the number of hosts available for B/Yamagata to infect. 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.
這個狀況有可能 在 2020 年初發生在 流感的 B/Yamagata 病毒種系上。 當世界很多地方都關閉、 保持社交距離、戴口罩, 以減緩新冠肺炎的散播, 能讓 B/Yamagata 感染的宿主也大大減少, 還需要再觀察幾個流感季節 才能肯定它是否真正絕種了, 或者只是躲藏在動物宿主身上。
Many viruses, as part of their life cycle, cause diseases severe enough to kill their hosts. 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.
許多病毒在生命週期中都會 造成嚴重的疾病,足以讓宿主死亡。 這可能是個問題,因為如果 病毒殺光了所有的宿主, 理論上,它可能會沒有剩下 任何宿主可以感染而絕種。
This almost happened back in 1950s Australia.
1950 年代在澳洲 就差點發生了這個狀況。
At the time, Australia was overrun by the European rabbit— an invasive species— 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. During the initial outbreak, as planned, tens, perhaps hundreds, of millions of European rabbits died. 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. With more infected hosts hopping around, this strain of the virus was more likely to spread than its deadlier cousin. And of course, rabbits evolved too, to mount better immune responses.
當時澳大利亞被歐洲兔子侵占—— 此兔是一種入侵物種—— 所以,為了試圖控制歐洲兔數量, 科學家釋放了一種病毒, 叫做黏液瘤病毒, 已知歐洲兔感染這種病毒的 致死率幾乎是 100%。 在疾病初次爆發時,如計畫, 歐洲兔的死亡數達數千萬, 甚至可能有數億隻。 但,隨著病毒散播, 病毒演化出了一系列突變種, 剛好變得沒有那麼致命。 殺死兔子的速度變慢了, 殺死的兔子總數也變少了。 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 更可能散播出去。 當然,兔子也會演化, 開始有更好的免疫反應。
Overall, instead of killing every single rabbit, the virus evolved, the rabbit population bounced back, and both survived.
總的來說,這種病毒沒有殺光 每一隻兔子,反而演化了, 兔子數量又再回升, 兩者都活了下來。
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——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. More on vaccination later.
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。 等下再回來談疫苗接種。
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. 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.
順便一提,病毒不見得 一定會彼此競爭。 病毒物種能夠開拓出 它自己的利基—— 比如,流感病毒會感染你的呼吸道, 而諾羅病毒會感染 你的腸道內的細胞, 所以這兩種病毒可以共存。
A virus’ ecological niche can be tiny: hepatitis B and hepatitis C viruses can infect the same cell— hep B occupies the nucleus, and hep C occupies the cytoplasm. In fact, epidemiologists estimate that 2 to 10% of people with hep C are also infected with hep B.
病毒的生態利基有可能很小: B 型和 C 型肝炎病毒 可以感染同一個細胞—— B 型肝炎病毒佔領細胞核, C 型肝炎病毒佔領細胞質。 事實上,流行病學家估計 C 型肝炎病毒帶原者有 2% 到 10% 也有感染到 B 型肝炎病毒。
So, will SARS-CoV-2— the species of virus that causes COVID 19— ever go extinct?
所以,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. Those variants might drive prior ones to extinction, or not. Regardless of how the variants compete (or don’t), the species itself— to which all the variants belong— is pretty firmly established among humans.
在這個物種之內還會 持續出現新變異株。 這些變異株有可能會讓 舊的變異株絕種,或者不會。 不論變異株如何競爭,或不競爭, 所有這些變異株所屬的這個物種 已經穩穩地在人類之中立基了。
If we managed to vaccinate enough people, could we drive SARS-CoV-2 to extinction? 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. 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.
如果我們有辦法 讓足夠的人接種疫苗, 有可能讓 SARS-CoV-2 絕種嗎? 我們針對天花做的 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。 但 SARS-CoV-2 可以躲在動物身上, 且我們目前的疫苗—— 雖然在避免重症和死亡的 保護力上很出色—— 卻無法預防所有的感染。
So, conceivably there are two ways that SARS-CoV-2— the entire species— could go extinct:
所以,可以想見,還有兩種 方式可以讓 SARS-CoV-2 整個物種有可能完全絕種。
a cataclysmic disaster could kill us all.
一場重大的災難 有可能讓大家同歸於盡。
Or...
或者,我們可能會發明出 一種通用的疫苗,
We could invent a universal vaccine that prevents all SARS-CoV-2 infections— those caused by all the variants that currently exist and those that don’t.
能預防所有的 SARS-CoV-2 感染, 目前既有的以及將來出現的 各種變異株所引起的感染。
Let's work toward that second option.
咱們朝第二個選項努力吧。