Redemption
Many of the characters throughout the text are given the chance for redemption. Most often this means a chance to take human form once more. For example Amy is changed back into human form in order for her to have the mental clarity necessary to defeat Zero. She was kept alive and save for all those years by Lucius for just that reason, to undo her failure the last time when she was bitten. Alicia nearly drowns, but somehow the shock of the incident reverses the affects of her virus so that she's clean again, although she chooses to commit suicide anyway. After retiring Peter gets back into the government game when the President asks. Eventually he becomes the new president, completely eliminating the reputation he had of quitting the first time when he retired. Each of these examples and more reveal individual opportunities for the characters to redeem themselves, but the theme of redemption is even more obvious when the book is considered as a whole. Humanity itself is fighting for survival against Zero and the virals, seeking a place which is safe from the contamination. Thanks to the heroic efforts of people like Michael and Peter, the last remaining humans do find this safe haven in the Atlantic Ocean. On this remote island they propagate and develop, eventually spreading onto the neighboring continents and restoring human civilization across the globe.
Sacrifice
The main characters of this book must be considered heroes. Each of them demonstrates a sacrificial willingness to participate in a cause which is greater than they are. In the end, they all -- except Amy, who pays her own price for immortality -- give their lives for the salvation of humanity. In the final conflict, Michael and Peter choose to stay and fight rather than sail away onboard the ship. This is an especially difficult decision for Michael because the ship has been his mission for over a decade now, his own invention. Not only does he give his life, but he gives all of his remaining time and ingenuity to outfit the ship in order to save the remaining humans. Finally, Amy gives her own blood to heal Peter after he's bitten. Although she defeats Zero, Amy is not freed. She has still been infected, so she is now immortal. When everyone else dies, Amy is left all alone in North America for centuries. She embodies the Christ figure from the Christian tradition by dying the first time when she was infected, saving the world, descending into purgatory -- her stint of solitude, -- and returning to teach the next generation. Quite literally, she embodies the savior role.
Loneliness
It's not surprising that people in this fictional timeline are suffering from severe loneliness. Since there are so few people left to begin with, those that find themselves separated from loved ones by necessity really feel the distance. At the very beginning of the novel, Alicia reminds readers about the fickle balance of life these days with the birth of her stillborn baby. Despite its being the product of rape, Alicia loved the child all throughout her pregnancy. She was absolutely crushed when the baby was born not breathing. As if a portent of the fate of all humanity, this infant is born having already died. Alicia takes two years to recover from the pain of her loss, living all that time completely alone. She spends her days training to track down and kill Zero. Her entire existence is based upon death, so it's no surprise that she kills herself in the end. Next Michael is introduced, having spent the last several years sailing around aimlessly. He is entirely alone. Since he could not return to his friends, he has spent years alone, looking for other people to help. Finally he gives up his journey to outfit the ship he finds in the Gulf in order to save what humans are still alive. For his part, Peter retires to a ranch in Texas. He's living a quiet life with just him and his nephew, but at night he dreams about another life with Amy. Each night he escapes into a detailed dream world where he's living with Amy, his true love. Even though he's not completely isolated like some of the other characters, he does pine for the one person who made him feel at ease.
