This equation was coined over 50 years ago:
Panspermia is the hypothesis that life can be transmitted through space. An example could be a very hardy bacteria in a meteorite. I saw a BBC Horizon programme where bacteria survived a simulated earth impact from space.
I'm actually not familiar with Drake's equation, but I would love to look it up and do some research. Are you able to loosely tell me about it? I'm also not familiar with Panspermia.