Are there any fifth world countries?

No. French Demographer Alfred Sauvy coined the phrase "3rd World" in 1952 as part of an economic differentiation of the world. The 1st World is the well developed countries of the West, the 2nd world were the less well developed countries of the Soviet Sphere, and the 3rd world is the group of developing countries that, at the time, both the 1st and 2nd worlds were trying to annex as ideological colonies.

You may be confusing that term with "5th Collumn", which is a term for a secret group that tries to disrupt a government during war.