A joint South Korea–U.S. research team announced findings that a COVID-19 vaccine booster shot (additional dose) does more than simply increase the number of antibodies; it strengthens the competitiveness of the immune cells themselves. It is akin to mobilizing the army and retraining it to boost fighting power. Thanks to this, the human body gains broader and stronger defenses even against variant viruses such as omicron.
A joint team from Washington University School of Medicine in St. Louis in the United States, Moderna, a COVID vaccine developer, and Korea University College of Medicine identified how a COVID-19 booster shot induces a broad immune response that can respond to multiple variants. The study was published on the 11th in the international journal "Science Immunology." Moderna developed a COVID-19 mRNA vaccine and received emergency use authorization from the U.S. Food and Drug Administration (FDA) in Dec. 2020.
The researchers observed how a fourth booster shot changes immune cells in nine healthy adults who had received three doses of the existing messenger RNA (mRNA) vaccine. The booster they received was a bivalent mRNA vaccine that simultaneously targeted the early form of the coronavirus that appeared at the end of 2019 and the omicron variant that emerged starting in Nov. 2021.
When a vaccine is administered, an immune response occurs in the lymph nodes (lymph glands) near the injection site. In the lymph nodes, "memory B cells" recognize the coronavirus surface protein produced by the mRNA vaccine as an antigen, an external invader. Later, when the coronavirus invades, another immune cell, the macrophage, awakens the memory B cells to produce antibodies. The antibodies trigger a neutralizing reaction that surrounds the virus and holds it to prevent infection of other cells.
The researchers collected a small amount of lymph node tissue with a thin needle and analyzed the immune cell response. As a result, the booster shot reactivated memory B cells formed by prior doses and summoned them to the core space of the immune response. It is akin to a situation similar to actual coronavirus infection. B cells again underwent maturation and selection, producing broad antibodies that could recognize not only the original coronavirus but also evolved variants.
In particular, the researchers found an antibody called mAb-52 in several study participants. This antibody showed the ability to neutralize multiple coronavirus variants and was also effective in preventing severe disease from omicron infection in hamster experiments, a rodent model.
These findings show that a booster shot not only increases antibody counts to strengthen existing immunity but also promotes renewed training of immune cells, guiding the process of generating antibodies that can respond to new variants. In other words, variant-responsive vaccines widen the breadth of immunity.
The researchers said, "Booster shots expand B-cell immunity against future variants," and noted, "This will be a key clue for developing vaccines to respond to variant viruses going forward."
Meanwhile, in Korea, COVID-19 vaccinations will begin on the 15th for seniors ages 75 and older. The Korea Disease Control and Prevention Agency said that those 75 and older or who are immunocompromised will be vaccinated starting on the 15th of next month, those ages 70–74 on the 20th, and those ages 65–69 starting on the 22nd, in sequence. Vaccinations will run through Apr. 30 next year.
High-risk groups such as adults ages 65 and older and immunocompromised people will be vaccinated free of charge. Members of the general public who are not high risk must pay the vaccination expense. Usually, one dose is sufficient, but immunocompromised children under age 12 need one to two doses.
Vaccinations are available at designated medical institutions and public health centers nationwide. Designated medical institutions can be found on the "Vaccination Helper" website. An ID card is required to receive the shot.
References
Science Immunology (2025), DOI: https://doi.org/10.1126/sciimmunol.adu4107