I read this sci-fi novel in the 80's. It is similar to the current TV series Alphas.
The story was about a young girl who ends up alone after some major disaster - a disease I believe. She thinks she is alone but eventualy discovers that there are others like her, other Alphas. She meets a young boy about her age who also believed he is alone, so they team up and travel across America to a location where they believe others like them are headed. Alphas are the next stage of evolution - smarter, stronger, healthier.
I have searched the web but can't find this book.