I thought it was very weak, with a few implausibilities. The "flu" epidemic had been building up for weeks and then, suddenly, everyone died in one night. The lack of bodies and damage, I would anticipate a lot more chaos and disorder if suddenly everyone started dropping like flies.
I'm glad that the scriptwriters are keeping to stereotypes and including a PC section of the population, not risking offending anyone. I'm also glad that the main protagonist has been to the "Eastenders and Soap Opera School of acting" which means that we are very ware that this is a play. Otherwise it would start to become real and might cause nightmares.
So, I'm waiting for the appearance of the evil scientist, the corrupt politician and the meglomaniac military man to tick all the boxes.
In other words... not well written and not well acted. My belief was not suspended!