Second COVID-19 Booster Dose Improves Efficacy Against Omicron Subvariants


After a second booster dose, efficacy against COVID-19 Omicron subvariants rose to 80% within the first 6 months, according to results of a study by the CDC.

A second booster dose was found to significantly improve efficacy against widespread COVID-19 variants Omicron BA.1 and BA.2/BA.2 12.1, according to the results of a study from the CDC.1

With the first booster dose, vaccine efficacy against the variants was only 68% and declined to 52% after 6 months, according to the CDC. However, after the second booster dose, efficacy against these variants rose to 80% within the first 6 months.1

There currently are no data available for the efficacy after 6 months.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," Shaun Grannis, MD, MS, vice president for data and analytics at Regenstrief Institute and professor of family medicine at Indiana University School of Medicine, said in a statement.1 "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 CDC currently recommends a second booster dose, or fourth overall for a primary 2-dose vaccine series, for individuals 50 years of age or older, as well as for those who are moderately or severely immunocompromised who are 12 years of age or older.1

The study was published in the CDC’s Morbidity and Mortality Weekly Report.1

For the study, the CDC collaborated with 7 US health care systems and the Regenstrief Institute to create the VISION network, which is used to assess the efficacy of COVID-19 vaccines.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 statement.1

In another study published in the Science, an additional booster dose could elicit sufficient immune protection against severe Omicron-induced COVID-19 disease.2

The study’s findings support evidence that a third vaccine dose expands the existing memory B cells in the bodies for the spike protein of COVID-19 infection, according to the authors. The results also support that the vaccine induces new memory B cells and the production of antibodies with enhanced potency against the Omicron subvariants.2

The investigators also found that the ability of the Omicron BA.5 spike to bind with the host receptor was more than 6 times stronger than the ancestral strain; however, all Omicron subvariants were slower at the next major step after binding with the receptor, which is fusing with the membrane of the host cell.2

The stronger binding could compensate for the slower time it takes to fuse with the host cell, the investigators said.2


1. Second mRNA booster significantly effective against Omicron variants, study finds. News release. Science Daily. July 18, 2022. Accessed July 25, 2022.

2. Booster shots offset some of Omicron immune evasion tactics. News release. Science Daily. July 19, 2022. Accessed July 25, 2022.

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