Is the COVID-19 Booster Shot the Same Vaccine as the First Two Shots?

Medically Reviewed on 12/1/2021
Is the COVID-19 Booster Shot the Same Vaccine as the First Two Shots
COVID-19 booster shots are the same formulation as the existing vaccines. However, the Moderna booster is half the dose of the previous two doses

COVID-19 booster shots are the same formulation as the existing vaccines. The additional vaccine dose strengthens the immune response of the standard vaccine course.

  • Johnson & Johnson: Booster is equivalent to the previous doses.
  • Pfizer: Booster is equivalent to the previous doses.
  • Moderna: Booster is half the dose of the first two shots. So, if you get the Moderna booster, it is a 50-mg dose rather than a 100-mg dose.

However, if you decide to get the Moderna booster, you may be offered a full third dose. That is because the FDA previously approved a third dose of Pfizer or Moderna for people who are immunocompromised.

Many people who have already been fully immunized against COVID-19 should be vaccinated again to remain protected. A booster dose can help protect you, your family, and your community against COVID-19.

What is the difference between a booster dose and an additional dose?


A COVID-19 booster dose is administered when a person has completed the single or double vaccine schedule and has a healthy immune system, but the protection against the virus has become less effective over time.

Additional dose

The goal of the additional dose is to improve the response of the initial vaccine shots in people who are immunocompromised.

Who will be offered a COVID-19 booster shot?

The CDC has recommended COVID-19 booster shots for:

  • Frontline health and social care workers
  • Those living in residential care homes for older adults
  • Frontline health and social care workers
  • All adults aged 18 years or older (depending on the vaccine received in the first dose)
  • All those aged 16-49 years with underlying health conditions that put them at higher risk of severe COVID-19
  • Adult caregivers
  • Adult household contacts (aged 16 years or older) of immunosuppressed individuals

Can I mix and match vaccines?

Yes, the FDA has approved mix-and-match vaccination and booster doses. The administration approved a plan that allows adults to choose whether they want their booster to be Pfizer, Moderna, or Johnson & Johnson, regardless of which type you got for your first series. 

The goal is primarily to make boosters more accessible. According to the FDA, mixing vaccines produces a stronger immune response than multiple doses of the same vaccine.

Are there any side effects of booster shots?

So far, it appears that the side effects of the booster shots are similar to what people experienced after the first doses of the primary series. After receiving the vaccine, you may experience mild to moderate side effects that usually subside after a few days. The most frequently reported side effects are:

Even if they receive the same vaccine, different people may experience different side effects. Symptoms can arise as a result of the immune-building process. These symptoms are normal and indicate that your immune system is reacting to the vaccine.

How helpful are the booster doses?

Booster doses have been shown in studies to significantly increase the protection against hospitalization and death. Evidence suggests that immunity against COVID-19 weakens in vaccine recipients of all ages. 

Vaccines initially appeared to be less effective in infection prevention, but they may decrease the rate of hospitalization and mortality. A small increase in the rate of hospitalization of fully vaccinated coronavirus patients suggests booster doses are required to prevent infection and ensure that breakthrough cases remain mild.

Researchers believe that the COVID-19 vaccine could become like a flu shot, administered 1-2 times a year. This could change depending on variants that may arise in the future.

Are COVID-19 vaccines and booster doses safe?

Vaccines must be proven to be safe and effective before they are administered in humans. COVID-19 vaccines and booster doses are no exception. COVID-19 vaccines have met the same safety standards as other vaccine trials.

Hundreds and thousands of doctors, nurses, seniors, and other frontline workers have proven that these vaccines are safe. Current recommendations advise pregnant women at high risk of exposure to SARS-CoV-2 (the virus that causes COVID-19) or those with comorbidities to get vaccinated after consulting their health care provider.

Why are people aged 12-17 years old not eligible for a booster when they can get a vaccine?

Booster doses are not currently recommended for those younger than 18 years old. Severe COVID-19 disease is uncommon in this age group. The primary course of COVID-19 vaccines generates a strong immune response, so the benefit from additional doses of vaccine is likely to be minor. 

Furthermore, there is currently very little information on the safety of repeated mRNA vaccine doses in this age group.

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Medically Reviewed on 12/1/2021
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Centers for Disease Control and Prevention. COVID-19 Vaccine Booster Shots.

Johns Hopkins Medicine. Booster Shots, Third Doses and Additional Doses for COVID-19 Vaccines: What You Need to Know.

US Food and Drug Administration. Coronavirus (COVID-19) Update: FDA Takes Additional Actions on the Use of a Booster Dose for COVID-19 Vaccines.