Background: Despite the global prevalence of SARS-CoV-2 reinfection, relatively little is known regarding its association with osteoporosis in older adults. This study investigated the potential impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection on bone health or osteoporosis risk in adults aged 55 years and older in Beijing, China, while also exploring additional factors that may influence this association. Methods: This cross-sectional study was conducted at Beijing Ditan Hospital, Beijing, China, between August and December 2024. Patients aged ≥ 55 years with SARS-CoV-2 infections were included. Data on demographic characteristics, lifestyle habits, diet, serum contents of 25-hydroxyvitamin D (25-OH-VD), and other potential risk factors for osteoporosis were collected through structured questionnaires. Bone mineral density (BMD) was assessed using dual-energy X-ray absorptiometry (DXA). To identify the variables associated with osteoporosis, logistic regression analysis was employed. Results: Three hundred and eighty-eight patients were enrolled, comprising 272 individuals with a single SARS-CoV-2 infection and 116 with two or more infections. The results revealed that individuals who had reinfection revealed a considerably higher prevalence of osteoporosis (48.3% vs. 17.3%, p < 0.0001). This trend was consistent across different skeletal sites: 33.6% vs. 7.4% at the left hip, 37.9% vs. 5.5% at the right hip ( p < 0.0001), and 30.2% vs. 12.9% at the lumbar spine (L1–L4) ( p < 0.0001). SARS-CoV-2 reinfection remained substantially associated with osteoporosis after controlling for con-founding variables, with an OR of 3.08 (95% CI: 1.696–5.593). Conclusion: In summary, the risk of osteoporosis among individuals with SARS-CoV-2 reinfection should be carefully monitored, and greater emphasis should be placed on early, individualized prevention and treatment strategies.

The 20 μg (0–1–6 month) hepatitis B virus (HBV) vaccination is widely recommended for HBV vaccine-naïve immune adults in China. However, suboptimal protective responses may occur due to dose-series incompletion. We aim to investigate the immunogenicity of a 60 μg HB vaccine with a 0–2 month series among HBV vaccine-naïve immune adults aged 25–55 to assess potential alternative approaches for HB immunization. A two-center randomized controlled trial was carried out. Participants were randomly allocated to either the 20 μg (0–1–6 month) or the 60 μg (0–2 month) regimen. Blood samples were collected eight weeks after the final injection to measure the antibodies. A total of 583 adults (289 in the 20 μg regimen and 294 in the 60 μg regimen) were included. The seroprotection rates (SPRs) were 97.23% and 93.54% in the 20 μg and 60 μg regimens, respectively (p = 0.0261), and the geometric mean concentrations were 600.76 mIU/mL and 265.68 mIU/mL, respectively (p < 0.0001). The immunogenicity of the 60 μg regimen decreased significantly with age, particularly in adults aged 40 and older. The 60 μg regimen may be beneficial for adults under 40, especially those with poor compliance or in urgent need of immunization.