The investigators will use previously characterised Good Manufacturing Practices-certified RSV and influenza viruses derived from recent clinical isolates to investigate the response to infection in healthy adult volunteers. Subjects will be recruited via advertisement and screened at Imperial College London. Healthy individuals will be enrolled in the study and undergo baseline investigations including sampling from blood, upper and lower respiratory tract. They will then be inoculated with RSV or influenza by intranasal drops and quarantined for 10 days. During this time, they will have further blood and respiratory sampling. After the 10 day isolation period, they will be discharged and followed up for up to 6 months post-infection.