The connection between the state of mind and the state of immunity explains why the death rate during Christmas and New Year peaked in camp and how a sudden loss of hope could kill people.
Book: Man's Search for Meaning
The death rate in the week between Christmas, 1944, and New Year's, 1945, increased in the camp beyond all previous experience. The higher rate wasn't caused by a harder working environment, a deterioration of food supplies, a change of weather, or new epidemics. It's simply because many prisoners had lived in the naive hope that they would be home again by Christmas. When they gradually found out that would not happen, they lost hope, and disappointment overcame them.
The connection between the state of mind of a person, their hope and courage, or lack of them, and the state of immunity of their body explain how a sudden loss of hope could kill people.
The ultimate cause of some's death was that the expected liberation did not come, and they were severely disappointed, which suddenly lowered their body's resistance against the latent typhus infection. Their faith in the future and their will to live had become paralyzed, and their body fell victim to illness.