Five weeks ago, you gave 72-year-old Sipho his annual influenza vaccine. Sipho had never reacted to any of the other vaccines given to him since birth, including his annual influenza vaccine which he had been receiving since turning 60. He was not taking any medication, but told you that he had a mild viral infection a few weeks prior. This was treated symptomatically, and he was over this episode when he came for his vaccination. Yesterday, his clearly distraught daughter brought him to the clinic, since he had developed weakness of the left side of his body and difficulty in breathing. He was admitted to the hospital and seen by the neurologist, and today you heard that the diagnosis is Guillain-Barré Syndrome (GBS).

The trigger event in this scenario is:
A. The vaccination received by Sipho
B. The infection that Sipho had a few weeks before receiving the vaccine
C. The daughter bringing Sipho to the clinic five weeks after you vaccinated him
D. The development of GBS symptoms