Doctor explains why the COVID-19 vaccine's 2nd dose has side effects Coronavirus vaccine second-dose side effects Many people who received both coronavirus vaccine doses say the second shot is worse than the first. We talk to a doctor about why that could be the case for some. As many people start receiving their second shot of the coronavirus vaccine, FOX 35 is looking into why some people have side effects from the second dose. "Anytime something foreign enters the body, the body sees it as that -- something foreign," Dr. Jason Littleton said. "It tries to recognize it. If it can’t recognize it. It tries to attack it."