Overview

• A study published in *Cell* demonstrates that same-arm booster vaccinations produce faster and broader antibody responses within the first week compared to alternating arms.
• Macrophages in lymph nodes near the injection site are primed by the initial dose and play a key role in orchestrating memory B cell responses to boosters in the same location.
• Human trials with the Pfizer-BioNTech COVID-19 vaccine validated findings from mice, showing enhanced early protection against Delta and Omicron variants with same-arm boosting.
• While antibody levels equalize after four weeks regardless of the injection site, the early immune advantage could be critical during outbreaks of rapidly mutating viruses.
• The research offers a pathway to refine vaccination protocols and informs the design of next-generation vaccines that may require fewer booster doses.