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Q: What is the difference between the third dose and a booster shot? I’m fully vaccinated against COVID-19. Should I get the booster shot?

There has been some confusion and misinformation on the COVID-19 vaccine “third dose” also sometimes referred to as the “booster” shot. Many are asking “what’s the difference?” and that is a great question.

The “third dose” of the vaccine, which is available now, is for the immunocompromised individuals who may not have benefited from the full efficacy of the two-shot vaccine series because of their compromised immune system. This can include people who are in cancer treatment, dialysis patients, and people with medical conditions that weaken the immune system, like HIV and sickle cell disease (a full list can be found on the Maui Health website at The third, additional dose, is needed to increase vaccine efficacy and essentially “catch-up” to the full protection the vaccine can provide. You can get a third dose if you meet health qualifications, had the Pfizer or Moderna vaccine, and if it has been more than four weeks since you received the second dose. If you received the Johnson & Johnson vaccine, you should not receive an additional dose at this time.

A “booster dose” will soon be offered to individuals who were fully vaccinated and are not immunocompromised, to provide a “boost” to increase vaccine efficacy, as the vaccine has been shown to decline in efficacy after a period of time. To receive the booster dose, you must be at least eight months past your second dose of either the Pfizer or Moderna vaccine. At this time, the Johnson and Johnson vaccine has not been approved for any additional doses. Per the CDC, once the booster dose is available to the general public, we will follow a similar phased rollout as the COVID vaccine, with healthcare workers qualifying first.

Both the third dose and the booster dose are administered in the same way and in the same dosage as the first and second dose.

Also, as a reminder, we are only administering the Pfizer COVID-19 vaccine in our clinic for first, second and third doses. For more details, please visit

Finally, we want you to know that the approval of the third dose and booster shots does not mean that the first two doses of vaccine were not effective. Studies continue to show that the vaccine provides lasting protection against COVID-19, and significantly reduces the chance of hospitalization and death. So, if you haven’t been vaccinated yet, it is still the best thing you can do to protect yourself and your loved ones.

Michael J. Shea , MD

Critical Care Medicine

Maui Memorial Medical Center
221 Mahalani Street
Wailuku, HI 96793