From what I’ve seen, gamma globulin shot is basically just the vitamin on steroids.
The flu shot however, actually adds a hidden, long-lasting status effect that reduces the odds of getting the cold and flu via other means.
Code excerpts, from Effects.Json:
{
"type": "effect_type",
"id": "common_cold",
"name": ["Common Cold"],
"desc": ["Symptoms alleviated by medication (cough syrup)."],
"apply_memorial_log": "Caught a cold.",
"remove_memorial_log": "Got over the cold.",
"apply_message": "You feel a cold coming on...",
"rating": "bad",
"resist_effects": ["took_flumed"],
"miss_messages": [["You're too stuffed up to fight effectively.", 1]],
"base_mods": {
"thirst_tick": [300],
"thirst_min": [1],
"fatigue_tick": [50],
"fatigue_min": [1],
"str_mod": [-3, -1],
"dex_mod": [-1, 0],
"per_mod": [-1, 0],
"int_mod": [-2, -1],
"cough_chance": [300, 0]
}
},
{
"type": "effect_type",
"id": "flu",
"name": ["Influenza"],
"desc": ["Symptoms alleviated by medication (cough syrup)."],
"apply_memorial_log": "Caught the flu.",
"remove_memorial_log": "Got over the flu.",
"apply_message": "You feel a flu coming on...",
"rating": "bad",
"resist_effects": ["took_flumed"],
"base_mods": {
"thirst_tick": [300],
"thirst_min": [1],
"fatigue_tick": [50],
"fatigue_min": [1],
"str_mod": [-4, -2],
"dex_mod": [-2, 0],
"per_mod": [-1, 0],
"int_mod": [-2, -1],
"pain_max_val": [15],
"pain_min": [1, 0],
"cough_chance": [300, 0],
"vomit_chance": [3600, 7200]
}
},
{
"type": "effect_type",
"id": "flushot",
"blocks_effects": ["flu"]
},