Years ago I had a Peanuts encyclopedia/big book o’ facts kind of book. One “fact” that always stuck with me was that there are over 180 different viruses that cause the common cold. Once you become infected with one you become immune to that particular virus and never get it again. This was from a book published in the 70s.
Does this “fact” resemble the truth in any way?
The “cold” virus mutates on a regular basis. There may have been 180 at one time (how would they know for sure?) but there are probably more now. You do get immunity to each one as you get it, which is why you don’t keep catching it back from your family members, but each year there are new ones.
Disclaimer: I’m a computer geek, not a doctor.
It’s true that the common cold is actually a class of rhinoviruses, each of which is distinct as far as your immune system goes but produces the same symptoms (broadly speaking). It’s false to try to count them all: Not only is it a large class, but each group is mutating rather rapidly (they have to go up against a dedicated immune system in each host, after all) and, sometimes, the definition of `species’ is a bit hazy.
As a side note, curing the common cold is damn near impossible for the above reasons. We’d need a hugely broad-spectrum antivirus drug that could catch all variants of the group of rhinoviruses without being defused by any mutations that group can undergo. Not killing the person would be a definite plus, too.
The latest I read is that there are about 500 different viruses that can cause colds, although as Derleth said they are constantly mutating. Moreover, you don’t get lifetime immunity from one virus. In fact, your immunity is short-lived because the IG involved is not of the long-memory variety. Immunity from one virus probably doesn’t last over a couple of months.