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We have coronaviruses. There is no "cold" virus really and it's an umbrella term for a few different viruses including coronaviruses. With human adapted coronaviruses - unlike zoonotic covid-19 - you don't get lifetime immunity https://www.ncbi.nlm.nih.gov/books/NBK7782/

You can just think of booster immunizations and getting tetanus shots when you're exposed. Why would you need those, otherwise? If you want to learn more looking into memory T and B cells.

I'm not certain if you are talking specific to coronavirus, but it is not unheard of with viruses. For example, chickenpox/shingles or herpes.

No, herpes, chickenpox + shingles would be the counter examples.

In my understanding, herpes and varicella (chicken pox/shingles) are thought to be "reactivations" of dormant viruses, not reinfections. The virus is never fully eliminated, and sometimes it becomes re-activated.