In which period are there no symptoms, but the person is actively passing the pathogen?

The incubation period is the correct choice because it is defined as the time between exposure to a pathogen and the onset of symptoms. During this period, an individual can be infected and actively shedding the pathogen without exhibiting any signs or symptoms of illness. This means that the person can still transmit the disease to others, even though they feel fine and may not be aware they are infected.

In contrast, during the prodromal period, the individual starts to present mild symptoms, indicating the development of the illness. The illness period is characterized by the presence of more severe symptoms as the disease fully manifests, while the recovery period comes after the illness, where the symptoms decrease and the person is regaining health. Therefore, it is during the incubation period that a person may unknowingly spread the pathogen while showing no symptoms at all.