International Journal of Clinical Case Reports, 2025, Vol.15, No.4, 190-199 http://medscipublisher.com/index.php/ijccr 194 Genetic differences and previous exposure to the influenza virus can also affect the response after vaccination. For instance, people with low antibody levels before getting vaccinated may actually experience stronger reactions. However, for those with already high antibody levels, the response was not so obvious (Song et al., 2010; Williams et al., 2022). Therefore, when vaccinating the elderly, a more suitable plan needs to be formulated based on individual circumstances (Bernstein et al., 1999; Castrucci, 2018). 5.2 The impact of chronic diseases Diabetes, heart disease and chronic kidney disease are very common among the elderly, and these diseases will further weaken the immune effect of vaccines (Figure 2) (Castrucci, 2018). Chronic diseases often lead to long-term inflammation and metabolic disorders, causing the immune system to age more rapidly and the body's response ability to vaccines to decline (Frasca et al., 2020; Mcelhaney et al., 2020; Sadarangani et al., 2022). For instance, elderly people in poor physical condition or with dementia usually have a poorer antibody response after vaccination than those in good health (Gross et al., 1989; Bellei et al., 2006). Figure 2 Geometric mean titers (GMT) pre-and post-influenza vaccine among full cohort for influenza A/HK/H3N2, A/MI/H1N1, and B-split, and among those with and without diabetes mellitus and obesity (Adopted from Sadarangani et al., 2022) Image caption: Panels a shows line graphs depicting GMT and 95% confidence intervals pre- and post-influenza vaccination for A/HK/H3N2, A/MI/H1N1 and B-split for the full cohort, subcategorized by their baseline seroprotection status (HAI of at least 1:40) for each respective strain. Panels b shows GMT and 95% confidence intervals pre- and post-influenza vaccination for the three strains amongst those with diabetes mellitus (n = 67) compared to those without. Panels c show GMT and 95% confidence intervals pre-and post-influenza vaccination for the three strains amongst those with obesity (n = 163, applying the same definition as in Tables 1 and 2) compared to those without. The embedded table displays the GMT and 95% CI data as shown in the corresponding panel line graphs (Adopted from Sadarangani et al., 2022) Some drugs required for chronic diseases, such as metformin, anti-inflammatory drugs and lipid-lowering drugs, may also have an impact on the immune system, thereby altering the effect of antibody production (Agarwal et al., 2018). However, if these chronic diseases are well controlled, the elderly can still achieve good vaccine effects, which also indicates that managing underlying diseases well is very crucial (Gross et al., 1989; Sadarangani et al., 2022).
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