This episode is the first where we really get to know Dr. Polaski and her ambitions and drive to help other people. She is in many ways similar to Picard – thus they don’t always see eye to eye. At the end of the episode they have a deeper understanding and respect for eachother.
The core premise of the episode is, that people were experimenting with genetics and created ‘super humans’ that have such a powerful immune system that it created a virus that kills humans… Nobody intended for this and it was not intentional from the ‘super humans’ (that are also just children, but well if you are 8 years old and fully grown, you are not a child)
It’s really weird to see that the genetic alteration thing is just brushed over and more a backdrop to the episode, while we would have stories like Star Trek 2: The Wrath of Kahn, or the entire backstory of DS9 Julian Bashier that takes a more critical look at it.
At the end of the episode, the Enterprise crew accidentally discovers that you can use the transporter to be immortal. By reversing all aging effects on the doctor by using some DNA they found in her quarters.