Vaccines save more than 9 million lives each year,even though they contain ingredients that can be prety dangerous.But that's precisely the point those nasty ingredients are the only reason that vaccines work at all.On their own,our bodies are already pretty good at fighting off illness.When an unfamiliar pathogen invades our body,patrolling immune cells engulf a few of these foes to gather intel.
疫苗每年能救900万人，虽然其材料中含有相当危险的成分。然而这些危险的成分，正是疫苗起作用的关键所在。我们的身体自带良好地疾病防御能力。当一种陌生的病菌侵入我们体内，巡逻中的免疫细胞会吞噬少量入侵物，收集相关信息。
The cells then churn out a chemical alarm,transmitting the enemy's information along the chain of command and triggering the production of specially-targeted antibodies and assassin cells to fend off the rest of the invaders.After the battle,some of these specialized troops stick around so that if the pathogen returns,they can help mount a quicker response.
然后释放出大量的化学警报，通过指挥系统传递入侵者的信息诱使身体产生特定的抗体，然后暗杀细胞会消灭剩余的入侵病菌。战役结束后，部分特攻部队会留守，如果该病菌再次入侵，它们能够快速做出反应。
However,some pathogens are so powerful that they can overwhelm the immune system before it's able to mount a defense.Vaccination lets us stage a practice version of this battle in advance of the real one,so that the immune system can develop and stockpile weapons specifically targeted at the enemy.That does require introducing a bit of the enemy into our bodies,but it's enemy that we've already disarmed,either by killing it,breeding a super weak strain,or dismembering it to get at recognizable-but not dangerous-parts.
然而，有些病原体太过强大，它们可以在免疫系统做出防御前，将其击垮。疫苗让我们在遭遇这类大战前，有机会提前进行演习，因此免疫系统可以开发并储备针对特定敌人的武器。这首先需要往身体里引进少量敌人，不过这些敌人的武器已经解除，它们不是死的，只是培养的特别弱的菌株，或是经过分解得到的可识别但不危险的部分菌体。
Enter formaldehyde.It's a critical ingredient in some common vaccines,like those for tetanus and influenza,because it alters the structure of those pathogens just enough to render them harmless.This reactivity also makes formaldehyde dangerous to us in large doses,but vaccines contain only a tiny fraction of the formaldehyde we consume and naturally produce on a daily basis.
丢进甲醛。甲醛是一种常见疫苗的鉴定材料，例如破伤风和流感，它能改变这些病原体的结构，使它们恰好变得无害。正因如此，大量甲醛也会对人体造成危害，但疫苗所含的甲醛，只是我们日常摄入和产生的甲醛中的一丁点儿。
In fact,the biggest risk with formaldehyde is that it can leave pathogens so crippled that they won't trigger the proper immune response.So some vaccines contain substances called "adjuvants,"which put the immune system on higher alert.
事实上，甲醛最大的危害在于它会重创病原体，令其无法触发适当的免疫反应。因此一些疫苗中含有“佐剂”它能令免疫系统处于高度敏感状态。
Aluminum,for example,causes a minor irritation at the infection site,summoning immune cells to the scene so they'll encounter the weakened enemy.And although too much aluminum can be toxic,our bodies are super-efficient at eliminating it,keeping levels low even after lots of shots.So while boatloads of aluminum,buckets of formaldehyde,and an up-close meet-and-greet with a full-strength pathogen are all definitely bad ideas,a controlled concoction from a doctor is designed to be just nasty enough to keep us safe.
例如铝会在注射部位造成轻度刺激，导致免疫细胞赶到现场，恰好发现虚弱的病原体。虽然大量的铝会造成中毒，不过我们身体消除铝的效率特别高，即使在大量注射后含量也会保持在低水平。因此，尽管混了铝，掺了甲醛，并且直接接触大量病原体，这些显然都很危险，不过医生那一管混合物其危险程度是设计用来保护我们健康的。
There's always a chance of an adverse reaction to a vaccine's ingredients,but the much scarier scenario would be to let polio,measles,and other deadly diseases call the shots.
接种疫苗存在一定程度的不良反应，但是感染小儿麻痹症、麻疹和其他致命疾病，显然更可怕。
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