The primary purpose of VAERS is to detect new, unusual, or rare adverse effects associated with vaccines. In particular, the system is used to monitor increases in known adverse events, to identify potential risks factors for particular types of adverse events, to identify vaccine lots associated with adverse events, and to assess the safety of newly licensed vaccines for general public. By monitoring such events, VAERS helps to identify any important new safety concerns and thereby ensure that the benefits of vaccines are greater than their risks (CDC, 2012).