CDC Study Finds Second COVID-19 Booster Defends Against Omicron Variants


The CDC published a new study, which found that a second mRNA booster shot would be effective against the Omicron variants of COVID-19.

A second mRNA booster shot is significantly effective against the COVID-19 Omicron BA.1, BA.2, and BA.2.12.1 variants, according to a study by the CDC.1

In the study, 214,487 individuals who went to the emergency department or urgent care (ED/UC) with COVID-19-like illnesses were studied, along with their vaccination status..2 Three doses of the vaccines were linked to higher vaccine effectiveness (VE) against ED/UC visits, and a fourth vaccine proved most effective.2

"The findings of this study are important because they provide an answer to a question that many people are asking: Should I get the second booster shot?” said co-author Shaun Grannis, MD, MS, vice president for data and analytics at Regenstrief Institute and professor of family medicine at the Indiana University School of Medicine.1

“The data clearly show that a second booster significantly increases vaccine effectiveness against these variants—which while no longer dominant in many areas, are still present,” Grannis said in the press release. “As we go into the fall, when viruses typically pick up, we want to encourage people who are eligible for a second booster to be proactive and to strongly consider getting one because it will provide greater protection. It will reduce the need for COVID-19-related emergency department visits and hospitalizations.”1

The first booster shot was originally 68% effective against these variants, but after 6 months it decreased to 52% efficacy.1 The second mRNA booster reached 80% efficacy within the first 6 months, and no data is available yet for the post-6-month mark.1

The study looked at the second booster and whether it reduced hospitalizations and emergency department (ED) visits caused by the widespread Omicron BA.1 and BA.2/BA.2.12.1 variants.1 The vaccine successfully protected against and prevented both hospitalizations and visits to the ED.1

The CDC recommends a second booster for individuals over 50, as well as the fourth shot of the vaccine for moderately or severely immunocompromised patients who are 12 years of age and older.1

"From a population health perspective, the protection supplied by the second booster helps ensure that health care resources are capable of responding to the full spectrum of medical needs, reducing the chance of overwhelming health systems with COVID-19-related disease," Grannis said in the press release.1

The study, called "Effectiveness of 2, 3, and 4 COVID-19 mRNA vaccine doses among immunocompetent adults during SARS-CoV-2 Omicron BA.1 and BA.2/BA.2.12.1 sublineage periods—VISION Network, 10 states, December 2021-June 2022," was published in the CDC’s Morbidity and Mortality Weekly Report on July 15, 2022.1


  1. Second mRNA booster significantly effective against Omicron variants. Regenstrief Institute. July 15, 2022. Accessed July 25, 2022.
  2. Beusekom, Mary Van. COVID-19 boosters offer good protection against early Omicron subvariants. University of Minnesota. July 18, 2022. Accessed July 25, 2022.,2.12.

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