Should healthy adults receive a Covid vaccine booster shot and why?

A booster shot of Covid vaccine (eg, mRNA, Pfizer or Moderna) is now recommended by the CDC even for healthy adults as follows:1

  • If you received Pfizer vaccine as your primary series, are ≥12 years old and at least 5 months after your 2nd dose
  • If you received Moderna vaccine as your primary series, are ≥18 years old and at least 5 months after your 2nd dose
  • If you received J&J vaccine, are ≥18 years old and at least 2 months after your 1st dose

There are at least 3 reasons for receiving a Covid vaccine booster: 1

  • Waning immunity after primary vaccine series
  • Emergence of Omicron variant which seems to be less responsive to the existing immunity from the vaccine
  • Recent data from clinical trials showing that a booster shot increased the immune response in trial participants who completed an either Pfizer or Moderna mRNA vaccine primary series 6 months earlier or had J&J vaccine single dose 2 months earlier

Here is the data from CDC on the vaccine effectiveness against Covid based on epidemiologic data on emergency department (ED)/urgent care (UC) encounters or hospitalization during the recent Omicron-predominant period:2

 Vaccine effectiveness against ED/Urgent care encounters 

  • 2 doses of mRNA vaccine: 41% (69% <2 months vs 37% ≥5 months after last dose)
  • 3 doses of mRNA vaccine: 83% (87% < 2 months vs 66% 4 months vs 31% ≥5 months)

Vaccine effectiveness against hospitalization 

  • 2 doses of mRNA vaccine: 55% (71% < 2months vs 54% ≥5 months)
  • 3 doses of mRNA overall 88% (91% if < 2 months, 78% if ≥4 months)

So take full advantage of available Covid vaccines and maximize your chance of not getting Covid!


Bonus Pearl: Did you know that a recent CDC study found that people 18 years and older who received the same mRNA vaccine brand for all their vaccinations experienced fewer adverse reactions following the booster dose than they did after their second dose of mRNA vaccine, with 92% of reported reactions not considered serious?3

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  1. Covid-19 vaccine booster shots. Feb 2, 2022.,after%20the%20J%26J%2FJanssen%20vaccine. Accessed Feb 24, 2022
  2. Waning 2-dose and 3-dose effectiveness of mRNA vaccines against Covid-19-associated emergency department and urgent care encounters and hospitalizations among adults during periods of delta and omicron variant predominance-VISION network, 110 states, August 2021-Jan 2022. Feb 18, 2022 Accessed Feb 24, 2022.
  3. New CDC studies: Covid-19 boosters remains safe, continue to offer high levels of protection against severe disease over time and during Omicron and delta waves. Feb 11, 2022. Accessed Feb 24, 2022


Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Mercy Hospital-St. Louis, Massachusetts General Hospital, Harvard Catalyst, Harvard University, their affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!

Should healthy adults receive a Covid vaccine booster shot and why?

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