Question

we know that once affected by smallpox when dont get it again because our immune system identifies it then why it does not happen with cold or cough or other kind of diseases?

Answer 1

beacuse smallpox's virus' structure always remains the same wheras there are numerous viruses which cause cold and they have ability to change their structure and therefore the WBC's cant identify them and attack them despite they a memory of virus causing cold but it was a different one earlier