These vaccines are very safe. Like other vaccines, a sore arm and brief flu-like symptoms of fever, fatigue, muscle aches and headache can occur. Some people get an enlarged lymph node for a few weeks under the arm. Rarely, people can have a serious allergic reaction, similar to what can rarely occur with other vaccinations. Inflammation of the heart muscle (myocarditis) has occurred after these vaccines but is generally mild and is also seen in people who have COVID-19. The inflammation of the heart that can occur with COVID-19 can be severe and even life-threatening. Overall, people are much more likely to get seriously ill from having COVID-19 than from getting vaccinated.