The real reason polio is so dangerous

翻译人员: Jing Quan 校对人员: Bruce Wang

In 1952, polio was everywhere.

1952年，小儿麻痹症无处不在。

For years, this virus killed or paralyzed roughly half a million people annually,

数年以来，这个病每年都会杀死或者致瘫 将近5千万人。

leaving survivors reliant on crutches, wheelchairs, and respirators.

残留下来的幸存者也必须依靠 拐杖、轮椅或者呼吸器来维持生命。

Yet just 10 years later, paralytic polio cases in the US dropped by 96%.

但就在十年后，美国的小儿麻痹症患者 数量下降了96%。

Soon, similar trends spread worldwide,

不久之后，类似的事情也相继在世界各地发生了。

and it looked like we were on track to eradicate polio for good.

看起来我们已经找到了彻底根除 小儿麻痹症的方法了。

But in the 21st century, the virus started striking back.

但是在二十一世纪， 这个病毒再度席卷而来。

So, what’s the source of these recent spikes,

那么，是什么导致了 最近病毒的激增呢？

and how can researchers fighting polio finally get rid of this deadly disease?

研究此病毒的人员又能通过什么方法 来完全根除这种致命的疾病呢？

To answer these questions, we first need to understand the true danger of polio.

要回答这些问题，我们要先了解 小儿麻痹真正的危害。

Most infected individuals only present mild flu symptoms or no symptoms at all,

大多数受感染患者都只呈现 轻微流感症状，甚至完全没有症状。

with paralysis occurring in less than 1% of cases.

麻痹症状在患病人群中的发生几率 不到百分之一。

Which is why the real danger of polio is how infectious it is.

这也就是为什么小儿麻痹症的 真正危害是它的传染性。

Historically, there have been three strains of poliovirus,

历史上来说，总共出现过 三种小儿麻痹症病毒。

all of which typically enter our mouths from airborne droplets

典型的传播途径是 空气传递的飞沫进入嘴巴，

or contact with infected fecal matter.

或者是接触到被感染的排泄物。

This means polio runs rampant in communities with poor sanitation.

也就是说，小儿麻痹症在 卫生设施缺乏的地区较普遍。

And once infected, individuals remain contagious for 3 to 6 weeks,

并且，一旦受到感染， 患者就会有三到六个月的传染期，

spreading a silent outbreak with few trackable symptoms.

无声地将这种 难以发觉的疾病扩散开来。

This is what made polio unstoppable

这也是小儿麻痹症无人能挡的原因。

until US physician Jonas Salk found a solution in the early 1950s.

直到1950年早期美国医生 乔纳斯·索尔克找到了治愈方法。

He created an inactivated version of the virus that, when injected,

他发明了一种未激活版的病毒， 这种病毒被注射后，

prevented all three strains from causing paralysis.

会阻止其他三种病毒引发麻痹症状。

However, this inactivated poliovirus vaccine, or IPV,

但是，这个未激活版的 小儿麻痹症疫苗（简称IPV），

didn’t stop poliovirus from living in our bodies and spreading to others.

并没有阻止小儿麻痹症病毒 留存在人们体内或传染给他人。

Fortunately, Polish American microbiologist Albert Sabin

幸运的是，与此同时， 波兰裔美国微生物学家阿尔伯特·沙宾

was creating the oral polio vaccine, or OPV, at the same time.

正在发明一种口服版麻痹症疫苗， （简称OPV）。

This even cheaper and easier to administer treatment

这种更便宜且易于管理的治疗方法

contained weakened variants of each poliovirus strain,

包含了减弱版的各类麻痹症病毒。

known as attenuated viruses,

也就是减毒病毒。

And once ingested, these prevented polio from settling in the body altogether.

注射后，这种疫苗就会 彻底阻止病毒留存于人类体内。

Over the next several decades,

在接下来的数百年，

IPV and OPV eliminated polio in country after country.

IPV和OPV在许多国家 根除了小儿麻痹症。

But near the turn of the century,

就在世纪尾声，

this arms race between medical ingenuity and viral evolution took a turn.

这场医学创新与病毒进化的竞赛 来了个大反转。

Scientists discovered variant strains of polio—

科学家发现了 小儿麻痹症的变异株，

each almost identical to one of the three existing strains.

每一个都几乎和 现存的三种病毒之一相同。

And their source was even more troubling.

其来源更加令人不安。

Up to this point, one of OPV’s greatest advantages was that its attenuated viruses

到目前为止，OPV的一个最大优势是 它是减毒病毒

could spread just like wild polio,

能像野生小儿麻痹症病毒一样传播，

moving through the air and immunizing unvaccinated individuals.

如通过空气传播， 帮助未注射疫苗的人提高免疫力。

But researchers discovered that if these weakened viruses circulated

但研究者发现，如果这些减毒疫苗

for several weeks in under-vaccinated populations,

在未接种疫苗的人群中传播数周，

they could mutate into new vaccine-derived strains.

也会变异成新的疫苗衍生毒株。

To be clear, this didn’t mean the attenuated vaccine

需要明确一点，这并不意味着减毒疫苗

was inherently dangerous.

本身具有危险性。

OPV had already been used to stop wild poliovirus type 2 worldwide

OPV已经在全球范围内用于 遏制野生型小儿麻痹症2类病毒，

and eradicate all wild poliovirus

并根除了来自美国、西太平洋

from the Americas, West Pacific, and countless other countries.

以及无数其他国家的野生型病毒。

The issue was ensuring populations met a certain vaccination threshold—

问题在于 确保民众达到一定的疫苗接种门槛——

specifically, at least 80% of every community needed to be vaccinated

具体来说，每个社区 至少 80% 的人需要接种疫苗，

to prevent strains from mutating.

以防止病毒株发生变异。

So, in our current fight against polio,

所以，目前我们与小儿麻痹症的斗争中，

we've taken two approaches to this problem.

我们正运用两种方法解决这个问题。

First, vaccine developers have made even safer forms of OPV.

一是，疫苗开发者 已经研制了更安全的进阶版OPV。

Monovalent and bivalent OPVs

单价和二价OPV疫苗

respectively contain one or two types of attenuated poliovirus,

分别包含一种或两种减弱病毒，

reducing the number of strains that could possibly mutate.

减少可能发生变异的毒株数量。

These vaccines helped eradicate wild poliovirus types 2 and 3,

这些疫苗帮助消灭 2类和3类野生型毒株，

and today they’re tackling the last remnants of type 1 poliovirus

如今，他们正在巴基斯坦和阿富汗

in Pakistan and Afghanistan.

处理剩余的1类毒株。

Vaccine researchers also developed OPVs targeting vaccine-derived polio.

疫苗研究员也研发了 针对疫苗衍生产生的病症的OPV。

Currently, most polio cases are caused by vaccine-derived poliovirus

如今，大多由疫苗衍生的2类毒株

type 2 outbreaks in Africa and the Middle East.

在非洲和中东爆发。

So researchers created a new vaccine specifically to tackle this strain

所以研究人员专门研发了 对抗该毒株的新疫苗，

with minimal risk of mutating.

以将变异风险降至最低。

Second, medical workers on the front lines are using cutting-edge technology

二是，工作在一线的医务工作者 使用前沿技术

to ensure every population meets that 80% threshold.

将疫苗注射覆盖80%的当地人口。

Digital tools like geospatial imaging and analysis

数字工具如地理空间成像与分析

help them locate and immunize remote communities.

帮助他们定位和免疫偏远地区。

Extensive monitoring systems ensure they don’t miss a single child.

广泛的监测系统确保他们 没有遗漏任何一个孩童。

And waste surveillance systems employed across the globe

全球废料监测系统

can alert us to potential outbreaks.

能警醒我们潜在的爆发风险。

Today, the fight against polio is at a critical moment.

现在，和小儿麻痹症斗争 正是千钧一发之际，

We’re primed to eradicate wild poliovirus in the near future,

我们准备在不久的将来 彻底消灭野生型该病毒。

and with our new vaccines,

用我们新的疫苗

eradicating vaccine-derived strains might not be much further off.

摧毁疫苗衍生毒株也将不再遥远。

But doctors still struggle to reach areas

但是医生仍然难以到达

experiencing military conflict and civil unrest.

正在经历战争和内乱的地方。

And without keeping vaccination rates high,

如果疫苗注射率不高，

polio’s silent outbreaks could easily surge.

那小儿麻痹症悄无声息爆发， 就会极易扩散。

So it’s essential that we keep up the pressure

所以我们必须施加压力

to finally finish what we started over 70 years ago.

以结束我们70年前就开始的斗争。