It's hard making antibodies, you should feel fatigue after your vaccination shot. It's your body creating antibodies but not after 4 days - if it persists could be another issue. Vaccines that have worked like Polio vaccines. There are good and bad vaccines. But the Covid vaccine is a "God send" according to Dr. Ray. 94% drop in symptomatic COVID cases among Israel's vaccinated - study
Anti-Vaxxers / Long haulers / staying indoors v being outdoors.