Most people may experience at least one side effect after getting their dose - the most common being an injection site reaction (e.g., pain, swelling, or redness). How many people experience Pfizer and Moderna side effects? More serious side effects, like a severe allergic reaction and myocarditis (heart inflammation) or pericarditis (heart lining inflammation), are very rare. Because of this, you may experience similar side effects with either brand, but they may be more noticeable after the second shot. The Pfizer and Moderna COVID-19 vaccines are the same type of vaccine - called messenger RNA (mRNA) vaccines. Pfizer and Moderna side effects after the second COVID-19 vaccine shot However, new data suggests a second dose of this vaccine can help provide additional protection against COVID-19. The Johnson & Johnson vaccine is a single shot. For more information on who currently should receive a third dose, click or tap here. A third dose is not currently required in other people who are fully vaccinated. The FDA has also authorized a third COVID-19 vaccine dose for select individuals with lower immunity and people over age 65. For both vaccines, you need both doses to be fully vaccinated. For the Moderna vaccine, you need to wait 28 days. For the Pfizer vaccine, you need to wait 21 days after the first dose to get the second dose. Which COVID-19 vaccines require a second dose?īoth the Pfizer and Moderna COVID-19 vaccines require two doses. We’ll take a look at how the immune system responds to vaccines, what the Pfizer and Moderna vaccine side effects are, and why they tend to be worse after the second shot. This phenomenon has to do with how vaccines help your immune system fight off infection. Many people have wondered why they have more intense side effects after getting the second shot of the Pfizer or Moderna COVID-19 vaccine.