NPR –
The vaccine and the tests are based upon different parts of the COVID virus. “All the vaccines in the United States use the spike genetic material,” says Kamil. “All of the home tests detect something called nucleocapsid,” a protein not found in the vaccine. But if the vaccine is going to make you feel ill, then how can you tell whether you’re sick from the vaccine or from a COVID infection? The answer to that question has to do with the timing and nature of your symptoms. As for how long your vaccine symptoms might last, Cohen says “everybody’s a little bit different,” but you should start to be concerned if you have a fever, body aches or headaches that last more than 24 hours.