Diabetes mellitus Affects Antibody Response to SARS-CoV-2 Vaccination in Older Residents of Long-Term Care Facilities: Data from the GeroCovid Vax Study

   ABSTRACT OBJECTIVE: Type 2 Diabetes mellitus may affect the humoral immune response following vaccinations, but data concerning COVID-19 vaccines are scarce. We evaluated the impact of diabetes mellitus on antibody response to the SARS-CoV-2 vaccination in older long-term care facilities (LTCF) residents and tested for differences according to anti-diabetic treatment. RESEARCH DESIGN AND METHODS: 555 older LTCF residents participating in the GeroCovid Vax study were included for this analysis. SARS-CoV-2 trimeric S Immunoglobulin G (anti-S-IgG) concentrations using chemiluminescent assays were tested before the first dose and after 2- and 6-months. The impact of diabetes on anti-S-IgG levels was evaluated using linear mixed models, which included the interaction between time and the presence of diabetes. A second model considered also diabetes treatment: no insulin therapy (including dietary only or use of oral anti-diabetic agents) and insulin therapy (alone or in combination with oral anti-diabetic agents). RESULTS: The sample's mean age was 82.1 years, 68.1% were women and 25.2% were diabetic. In linear mixed models, the presence of diabetes mellitus was associated with lower anti-S-IgG levels 2 (β=-0.20, 95%CI:-0.34,-0.06) and 6 months (β=-0.22, 95%CI:-0.37,-0.07) after the first vaccine dose. Compared to those without diabetes, diabetic residents not using insulin had lower IgG levels at 2- and 6-month assessments (β=-0.24, 95%CI:-0.43,-0.05, and β=-0.30, 95%CI:-0.50,-0.10, respectively), while no differences were observed for those under insulin.  CONCLUSION: Older LTCF residents with diabetes tended to have weaker antibody response to COVID-19 vaccination. Insulin treatment might buffer this effect and establish a humoral immunity similar to non-diabetic individuals.</p