Vaccine side effects, such as headaches, fevers and chills, are a sign our immune system is building protection against the virus we are being vaccinated against.

When we receive an mRNA vaccine (Moderna or Pfizer), the vaccine tells our cells to build copies of the spike protein found on the surface of the virus that causes COVID-19. It’s impossible for these spike protein copies to infect us with COVID-19. But our body sees a protein it doesn’t recognize and launches an immune response to build antibodies. Even if those antibodies do not prevent infection, they, along with memory –B and –T cells, can respond immediately and reduce the length and severity of illness. People who are not vaccinated were 17 times more likely to die from COVID-19 in March than those who received a primary vaccine series plus a booster dose.

Severe adverse events from vaccination are rare.

Anaphylaxis is a severe allergic reaction that may occur within minutes after receiving any vaccination. For COVID-19 vaccinations, it has occurred at a rate of about five cases per 1 million vaccinations.

Myocarditis is inflammation of the heart muscle, and pericarditis is inflammation of the outer lining of the heart. These reactions are rare and happen most often in teenagers or young adult males, usually within one week of receiving an mRNA COVID-19 vaccination (Pfizer or Moderna). CDC data show myocarditis occurs less often after a booster dose than the second dose in a primary vaccine series. Symptoms include chest pain, shortness of breath and a fast-beating, fluttering or pounding heart. Most patients respond well to treatment of their symptoms and feel better within a few days.