You have to separate infections from poisonings. You can drink cyanide right now and be dead in 30 seconds. Or eat Amanita mushroom and be dead in 3 hours. But that’s because the mushroom already contains the neurotoxin! An infection, by definition, involves replication of the foreign organism within your body, and that takes time. E.coli bacteria are some of the fastest replicators, and they still take 45 minutes per division at minimum. There is only so fast they can physically duplicate DNA and assimilate foreign molecules. And you need multiple successive divisions to build up a population to count as an infection - on the order of days. Viral infections can grow even faster than bacterial, but they still take time. COVID is one of the most infectious viruses known, and it still takes 3-5 days from exposure to symptom onset. The fastest colds take ~24 hours. Not minutes! Even if you have the most advanced militarized bioweapon zombie virus, you cannot bypass the laws of physics - DNA is still replicated at 100 nucleotides per second. Whatever is causing someone in the movies to turn into a zombie in minutes is not an infection, it is a brain-killing neurotoxin at best.