十万个为什么·科学启蒙30篇（2）

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疫苗是如何训练免疫系统的？

Vaccines introduce harmless versions of pathogens — such as dead viruses, weakened live ones, or just key protein fragments — to safely mimic infection.
Specialized immune cells called dendritic cells recognize these foreign markers and activate T-cells and B-cells to mount a targeted response.
B-cells produce antibodies that latch onto specific antigens, while memory cells remain in the body for years — ready to respond faster if the real pathogen returns.
Some vaccines require booster shots because immunity fades over time or because the pathogen mutates rapidly, like influenza viruses.
mRNA vaccines work differently: they deliver genetic instructions so your own cells temporarily make harmless spike proteins, triggering immunity without using any virus.
Herd immunity occurs when enough people are vaccinated, making it hard for diseases to spread — protecting those who can’t be vaccinated for medical reasons.
Before vaccines, measles killed over 2.6 million people annually worldwide; today, vaccination prevents an estimated 4–5 million deaths each year.
Side effects like sore arms or mild fever are normal signs that your immune system is learning — not evidence the vaccine is dangerous.