He didn’t exactly blow up the CDC—it blew up on its own because it couldn’t store the virsus safely.
But even if Rick thought Jenner was nuts, wouldn’t the two non-bitten dead guards at the school (or whatever that place was where they went to drop off the kid) have given him a clue that Jenner was right?
Yeah, you’re right but he wouldn’t be absolutely sure until he saw it happen himself (Shane)
Probably didn’t want to believe it.