The movie 28 Days Later and the Music Video for "Party Rock Anthem" are linked.
When the virus gets to the United States, it mutates to make people dance. Everyone thinks it's the song that caused people to dance, but it's just coincidence the virus arrived when the song became a hit.

LMFAO's hiatus was caused by creative differences.
One of them wanted to focus more on the "Partying" while the other wanted to focus more on the "Rocking".