When I started watching this, I knew that it was set in a post-pandemic world, but I sort of thought that this would have some kind of space element; think "The 100"  or "The Martian" or something like that.  It did not! If you're curious about the plot, have a look at the book's wikipedia page (the TV show wikipedia page has a poor synopsis, oh yeah...spoiler alert).  The story was pretty cool, and it's told asynchronously, jumping between three different time frames (if I remember correctly). The big reveal comes at the end when all the threads are tied together.  I wasn't a big fan of the first few episodes because it wasn't readily apparent to me what was happening, but the ending was satisfactory and it did pay off in the end.

As an aside, it's interesting how all these global catastrophe movies and video games (caused by viruses or microbes) end up with the fall of civilization, but even with COVID we're still here ;-)