Virus Blast is one of my first middle sized games. It is a small popper game with around 250 levels and all you need to do is to touch red viruses to start reaction. You need to initiate chain reactions to minimize your steps and win level. Game has small tutorial at the beginning and then 5 different level packs with 40-60 levels in them. Game is released in 4 stores iTunes, Samsung, Amazon, Google Play. Here are the links to download the game:
Here is a small video which demonstrates gameplay.