I’ve been mildy sick for a while now – almost three months I’d say. It’s just an everyday cold, though I’m pretty sure I caught a different cold virus on top of that a few days ago.
Wondering whether I should be concerned or not, I did a quick google. Looks like this is a rather common question, and the phenomenon is called a superinfection.
Long story short, the local immune response to two different rhinoviruses (aka the common cold) will essentially be the same. These include macrophages (i.e. the gross green stuff you blow out of your nose, or cough up out your lungs), which just needs to “eat up” the virus to disable it.
The adaptive immune response (B-cells and T-cells) might have a tricker time due to two different activating signals, but the two sets of viruses will be in competition with each other for resources (cells to kill) at the same time, so.
TL;DR: contracting two different strands of the common cold is nothing to be concerned about.
So when should one be concerned with a superinfection?
When you contract two different types of infections, say, viral and bacterial. The immune responses to viral and bacterial infections are quite different, and one may be counterproductive to the other.
For example, most people that “die of the flu” actually die from bacterial infections of the lung that were able to gain a foothold because of the immune response to the flu virus.