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However—and this is critical—protection against severe disease has remained much more stable.
🛡️ Immunity Isn’t a Permanent Shield
Another reason vaccinated individuals may still get sick is that immunity naturally wanes over time.
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After vaccination:
Antibody levels peak
Then gradually decline
Memory cells remain for long-term protection
This means that months after vaccination, your body may not prevent infection as effectively—but it can still respond quickly to fight the virus.
This is why booster doses were introduced: to “remind” the immune system and strengthen protection, especially for vulnerable populations.
🧑⚕️ Individual Differences Matter
Not all immune systems respond the same way.