Catch cold VS catch a cold

[SARDORBEK]

Dear TEACHER!

I have come across the two similar expressions below many times,
but I'm not sure about their difference:

1) You'll catch cold if you go out like that. (M.Hewings - Advanced Grammar in Use)
2) You'll catch a cold unless you wear your coat (Jenny Dooley & Virginia Evans- Grammarway № 2)

In reference to the usage of indefinite article what is the difference between them
all things considered (formality, variety etc.. of English)

Many thanks...

[Alan]

There is virtually no difference.