Question

Is this a complete sentence? Diphtheria is rare in North America and Europe, it's still common in countries without readily available vaccinations.

Answer 1

Answer: nope

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Answer 2

I do not think that is a complete sentence.

Step-by-step explanation:

This is because when a reader reads your sentence, it doesn't emphasize how Diphtheria is still "common" in other countries. So the best way to write this sentence is:

Diphtheria is rare in North America and Europe. However, it's still common in countries without readily available vaccinations.

Or

Diphtheria is rare in North America and Europe. Although, it's still common in countries without readily available vaccinations.

You have to make sure your sentence has full meaning. Using a transition is better than using "and" or a comma by itself. That is because "Diphtheria is rare in North America and Europe." is already a complete sentence. If you placed a comma between the two, it will be looking like a run off sentence.