The total symptom score (TSS) is the sum of the 8 single common cold symptom scores consisting of 3 systemic (headache, muscle ache and chilliness) and 5 local (sore throat, blocked nose, runny nose, cough and sneezing) symptoms. Each common cold symptom was scored on a 4-point ordinal scale: 0 = symptom not present 1 = mild symptom (I can feel it but it has not disturbed or irritated me) 2 = moderate symptom (symptom has disturbed and irritated me some of the time) 3 = severe symptom (symptom has disturbed and irritated me most of the time) The mean over days 2 to 4 (TSS2-4) was calculated as (TSS2 + TSS3 + TSS4)/3 where TSS2, TSS3 and TSS4 are the total symptom scores calculated for days 2, 3 and 4 respectively. TSS2-4 ranges from 0 (no symptoms) to 24 (severe symptoms).