Elevated BMI reduces the humoral response to SARS‐CoV‐2 infection

OBJECTIVE: Class III obesity (body mass index [BMI] ≥ 40 kg m(−2)) significantly impairs the immune response to SARS‐CoV‐2 vaccination. However, the effect of an elevated BMI (≥ 25 kg m(−2)) on humoral immunity to SARS‐CoV‐2 infection and COVID‐19 vaccination remains unclear. METHODS: We collected blood samples from people who recovered from SARS‐CoV‐2 infection approximately 3 and 13 months of post‐infection (noting that these individuals were not exposed to SARS‐CoV‐2 or vaccinated in the interim). We also collected blood samples from people approximately 5 months of post‐second dose COVID‐19 vaccination (the majority of whom did not have a prior SARS‐CoV‐2 infection). We measured their humoral responses to SARS‐CoV‐2, grouping individuals based on a BMI greater or less than 25 kg m(−2). RESULTS: Here, we show that an increased BMI (≥ 25 kg m(−2)), when accounting for age and sex differences, is associated with reduced antibody responses after SARS‐CoV‐2 infection. At 3 months of post‐infection, an elevated BMI was associated with reduced antibody titres. At 13 months of post‐infection, an elevated BMI was associated with reduced antibody avidity and a reduced percentage of spike‐positive B cells. In contrast, no significant association was noted between a BMI ≥ 25 kg m(−2) and humoral immunity to SARS‐CoV‐2 at 5 months of post‐secondary vaccination. CONCLUSIONS: Taken together, these data showed that elevated BMI is associated with an impaired humoral immune response to SARS‐CoV‐2 infection. The impairment of infection‐induced immunity in individuals with a BMI ≥ 25 kg m(−2) suggests an added impetus for vaccination rather than relying on infection‐induced immunity.