The bulk of the morbidity and mortality related to asthma is during periods of acutely increased symptomatology called 'exacerbations'. Roughly half of asthma sufferers experience such an exacerbation each year. Most of these events are triggered by viral infections, usually the common cold virus (rhinovirus). A key part of the body's defence against viral infections is to produce antiviral proteins called 'interferons', which have a myriad of effects to stop viruses. Previous work on cells taken from volunteers with asthma and healthy controls and infected with rhinovirus in the lab suggests interferon production is impaired in asthma. However when human volunteers with asthma are infected with rhinovirus, high levels of interferon are found a few days later - along with high numbers of virus. Whether the high virus numbers are the result of an initially weak interferon response, with subsequently unchecked viral replication leading to exaggerated interferon levels, is unknown as no one has measured interferons early in infection. By infecting volunteers with asthma and healthy controls with rhinovirus at a known time, only done in a handful of centres worldwide, we will be able to measure interferons within hours of infection and well before symptoms develop.