For example, the flu vaccine has many side effects, such as low fever, swelling at the injection site, redness, itching, fatigue, headache and many others. The flu vaccine is also not recommended for people allergic to eggs. Diphtheria, tetanus and acellular pertussis, also known as DTaP is one of the most common vaccines required for children, it also comes with many side effects such as fever, swelling, redness, soreness, tenderness at the injection site, poor appetite and vomiting may also occur. According to CDC.gov, there are many problems that can occur after any vaccine, even if severe reactions are very serious