Getting a flu shot causes people to contract the flu.
The seasonal flu vaccine is inactivated (dead) virus, not live virus, and therefore cannot replicate or cause infection. Some people experience mild symptoms like soreness, low-grade fever, or body aches after vaccination, these are signs of immune system activation and inflammation, not influenza itself. True influenza involves high fever, respiratory symptoms, and myalgia lasting 5-7 days; post-vaccine soreness resolves in 1-2 days and isn't accompanied by the systemic illness of actual flu. Studies comparing vaccinated and unvaccinated populations consistently show that vaccinated people experience fewer influenza cases and milder illness when they do get infected. The perception that 'the vaccine gave me the flu' likely stems from coincidental timing: flu season peaks in winter, the same time when many people get vaccinated. Someone vaccinated in November who gets sick in December may assume causation, when in fact they encountered wild virus. A 2017 meta-analysis of over 20 studies found no increase in respiratory illness in vaccinated versus unvaccinated groups, the vaccine does not cause flu and provides 40-60% protection in good years.