Upon intranasal vaccination, live attenuated influenza vaccine (LAIV) viruses may replicate within the nose for several days. Current clinical diagnostic tests cannot distinguish between LAIV viruses and multiple influenza viruses in recently inoculated patients that present with respiratory symptoms. This poses a problem for the diagnosis and treatment of patients with respiratory symptoms, as these symptoms may not be caused by influenza. CDC researchers have developed a real-time RT-PCR assay to detect the presence of LAIV viruses. This test is rapid, accurate, and provides diagnostic data about whether patient respiratory symptoms are due to wild-type influenza or LAIV viruses. Detection of LAIV viruses with this assay will allow practitioners to investigate other pathogens as causative agents for a patient's respiratory symptoms.