2.7. Randomization
COLD, COMMON COLDS
Participants were randomly divided into two groups in a 1:1 ratio using block randomization by an independent investigator. The stratification factor was the number of times they had contracted a cold in the past 3 years (0, 1–2, or more than 3). However, the allocation was performed by number of common colds in the past 3 years (0–1, 2, or more than 3), so there was a deviation from the protocol. The allocated sequence was sealed to both participants and investigators until the study ended and the database was locked.