Lay summary
New Zealand has high rates of asthma and hospitalisations for asthma. Viral respiratory infections are the most common cause of asthma exacerbations in both children and adults. Preliminary laboratory and clinical evidence points to carrageenan nasal spray (an extract of red seaweed) being a potentially exciting new treatment for cold virus infections. This study will investigate how effective using a nasal spray containing carrageenan is as a treatment against the development of asthma exacerbations caused by rhinovirus cold infections, in adults with a history of severe asthma exacerbations. The use of carrageenan during a cold has been demonstrated to reduce the severity of cold symptoms by reducing viral load; we believe that this reduction will also decrease asthma exacerbations.