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  • ["An inefficient virus kills its host. A clever virus stays with it." - James Lovelock]

    [「無效的病毒會殺害宿主、聰明的病毒會與宿主共存。」 - James Lovelock]

  • 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 appearDelta.

    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?


  • 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,

    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.


  • 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?


  • 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:


  • 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.


  • 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.


  • There are three main ways that can happen.


  • First, a virus could run out of hosts.


  • 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.


  • 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.


  • 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.


  • 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.


  • 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.

    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.


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


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


  • 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.


  • 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.


  • 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.

    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.


  • Those variants might drive prior ones to extinctionor not.


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


  • 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.


  • 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 speciescould 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.


  • Let's work toward that second option.


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


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


["An inefficient virus kills its host. A clever virus stays with it." - James Lovelock]

[「無效的病毒會殺害宿主、聰明的病毒會與宿主共存。」 - James Lovelock]

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持續多年的新冠肺炎始終沒有結束跡象!看看影片了解終結病毒的三種方式(3 ways to end a virus)

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    shuting1215 發佈於 2023 年 02 月 05 日