十万个为什么·科学启蒙30篇（2）

26 / 30

疫苗是如何帮助身体抵抗疾病的？

Vaccines contain weakened or inactive parts of a virus or bacteria.
When injected, they safely train your immune system to recognize real threats.
White blood cells learn to make special proteins called antibodies against the invader.
If the real disease enters your body later, your immune system responds much faster.
This rapid response often stops illness before symptoms even begin.
Some vaccines require multiple doses to build strong, lasting protection.
Herd immunity occurs when enough people are vaccinated to block disease spread.
Vaccines have helped eliminate deadly illnesses like smallpox worldwide.
Scientists continuously update flu vaccines because flu viruses change every year.
Side effects are usually mild, such as soreness or a low fever for one or two days.