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疫苗如何帮助身体抵抗疾病？

Vaccines contain weakened or dead germs, or just parts of them, that cannot cause serious illness.
When injected, they teach your immune system to recognize dangerous invaders without making you sick.
White blood cells quickly identify the vaccine material and produce special proteins called antibodies.
Memory cells store this information so your body reacts faster if the real germ returns later.
Some vaccines need booster shots because immunity fades slowly over many years.
mRNA vaccines, like those for COVID-19, give cells instructions to build harmless virus pieces.
This tricks the immune system into preparing defenses before actual infection occurs.
Vaccines have helped wipe out diseases like smallpox and nearly ended polio worldwide.
Herd immunity protects vulnerable people when enough community members are vaccinated.
Doctors test vaccines many times to ensure they are both safe and strongly effective.