This study investigates multiple vaccine strategies to enhance immunogenicity and protection against SARS-CoV-2 in aged mice. The study aims to determine the effect of a booster dose, with an emphasis on older age. Female three and eleven-month-old BALB/c mice were studied over the course of 38 weeks. Mice received BNT162b2 SARS-CoV-2 spike mRNA vaccine series, primary vaccination series, and mock Phosphate-buffered saline (PBS) injections. Single mouse experiments aimed to include 20 mice per group. Sample size and age criteria were chosen empirically based on the results of previous studies. Mice were randomly assigned to different treatment groups.