The reputed story of "Ring Around the Rosie" was told summarily in the episode. The part about the 'ring around the rosie' applies to the initial rash. 'Ashes ashes' refers to the marks they would put on doors to indicate households with the infected. 'All fall down' applies to the infected quickly dying.
The plague must indeed have felt like the end of the world; the apocalypse.
Filmed on Catalina Island off the coast of Long Beach, California. Island is known as "Catrina Island" in the episode.
First use of the word "apocalypse" within the Walking Dead franchise whereas most often everyone uses the term "end of the world."
In this episode, we learn that other countries outside of the USA have been affected. Vancouver has fallen, and Mexico has closed its borders.
The song that Alicia is listening to while she walks around the island is "Coxcomb Red" by Ohio.