The study you are linking to was not comparing flying to not flying, only two different groups flying. Consider that the baseline rate of colds in a seven day w

The study you are linking to was not comparing flying to not flying, only two different groups flying. Consider that the baseline rate of colds in a seven day window (their before travel to after travel survey window) is very high: https://www.cdc.gov/mmwr/volumes/69/wr/mm6914a5.htm https://www.cdc.gov/mmwr/volumes/69/wr/mm6914a5.htm