Viruses and other infectious organisms have been around since long before humans walked the planet. While many microorganisms are helpful and necessary for human survival and function, others bring disease and death. Immunity is what prevents humans from being wiped out by a particularly virulent bug.
The CDC defines immunity as “protection from an infectious disease. If you are immune to a disease, you can be exposed to it without becoming infected.”
How does one achieve immunity? As the CDC explains, there are two ways.
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