When is it safe for a newborn to travel via plane internationally? how old must they be?

At any time: It is safe to travel with an infant at anytime. The ventilation in an airplane is not very good and that is why many germs are airborne, but that would be only downside to flying with a newborn.

Depends on situation: During a stint in the military, i routeinly discharged newborns that traveled to the airport for a flight back to the US for their first month or two before returning to Japan. They traveled better than most toddlers or older kids.Considerations such as infectious exposure in transit, risk at the destination ; availability of health care factor in. Live life but plan ahead to protect baby.