Brought my baby to HK (via CX) when she was 7 months as well! Agree with Mei that it's really more an issue of logistics planning than health risk.
If you want to be sure, ask your PD for a go signal based on your baby's history of health. I actually asked mine if there were any additional vaccines we had to take since we'll be in an enclosed space with people (and their viruses) from all over the world. But she said no need.
HKG is a very family-friendly airport. On our way home, baby was asleep in the stroller and we didn't have to take her out from check-in all the way to boarding, using "family lanes"! They even had a female security personnel check our stroller because my baby is a girl.