The Eleventh Plague

In the start of the book the main character Steven and his dad are traveling through the 2/3 infected United States when they see an unidentified air craft then they start to investigate. When they do they find some supplies that will help them during their travel like food water until a loud rapid gun fire sounds. And army troops start to come out of the nearest forest. Then a wagon pulls up gets Steven and his dad inside and out runs the troops then they take them to a secret neighborhood where they stay.