human
I've heard that the flu vaccine can cause side effects. How severe are these side effects?
assistant
The most common side effect is a sore arm or shoulder, but this is usually mild and only lasts for a few days. Other less common side effects include headache, fever, muscle aches, fatigue, nausea, vomiting, and dizziness. These symptoms may last for up to two weeks, but are usually mild and go away on their own.