The document discusses how systems biology approaches can help improve vaccine design and testing. Researchers are able to measure immune system responses to potential vaccines at the genetic, protein, and cellular levels. By analyzing these complex data sets, they can identify signature profiles of protective immunity and use them to guide vaccine development. This allows them to quickly evaluate many candidates and focus on improving the most promising ones. The approach has provided insights into why some vaccines like yellow fever are highly effective. Researchers are now applying these methods to develop an HIV vaccine by studying immune responses in monkeys infected with simian immunodeficiency virus.