Impact of Nutritional Status on Antibody Titer After Booster mRNA COVID-19 Vaccine Among Elderly Adults in Japan.

BACKGROUND: Published studies on mRNA coronavirus disease 2019 (COVID-19) vaccine effects focus on younger individuals, comprising the majority of the workforce. Studies in elderly adults are sparse. METHODS: In total, 107 subjects were recruited (median age 78; interquartile range [IQR], 58.5-90.5; range, 35-105 years). Factors associated with antibody titer after the third mRNA COVID-19 vaccination were compared between 49 elderly (age ≥80; median, 94; IQR, 86-97; range, 80-105 years) and 58 younger (age ≤79; median, 61; IQR, 46-71; range, 35-79 years) adults. RESULTS: Among body mass index (BMI) categories, the group of underweight elderly adults had a lower antibody titer compared to those with normal weight (P < .01 after 1, 3, and 5 months). Elderly adults were less likely to maintain effective antibody titer (≥4160 AU/mL) compared to younger adults: 76% versus 98%, P < .001 after 1 month, and 45% versus 78%, P < .001 after 3 months. Elderly adults who maintained effective antibody titer for 5 months had a higher BMI (22.9 kg/m2 vs 20.1 kg/m2, P = .02), and were less likely to have underweight BMI (0% vs 31%, P = .02) compared to the subjects who failed to maintain effective antibody titer. CONCLUSIONS: These results highlight the impact of nutritional status and the deleterious effect of underweight BMI on antibody titer and its maintenance among elderly adults following booster mRNA COVID-19 vaccination.