Assessing the relationship between body mass index and influenza-like illness risk and symptom severity among military health system beneficiaries vaccinated against influenza: a pooled prospective cohort study from a randomized trial.

INTRODUCTION

Obesity prevalence is rising globally and associated with increased influenza mortality. The relationship between obesity and influenza-like-illness (ILI) incidence and symptom severity is less clear.

MATERIALS AND

METHODS

US Military Health System (MHS) beneficiaries enrolled in a randomized influenza vaccine trial received one of three influenza vaccines and were followed for ILI via weekly surveys throughout one influenza season. Participants were pooled across vaccine arms into a prospective cohort. We compared ILI risk and ILI symptom severity (Flu-PRO) across body mass index (BMI) categories using multivariable regression models.

RESULTS

Among the 8,334 participants with >50% response rates to weekly ILI surveys, 42% had an overweight-range BMI and 24% had an obesity-range BMI. The median age was 36.2, and 86% had no baseline comorbidities. Over one quarter of the participants (27%) reported at least one ILI during follow-up, with a median duration of 11 days. Participants with an overweight and obesity-range BMI were more likely to report ILIs [adjusted incidence rate ratio (aIRR) 1.18 (95% confidence interval (CI): 1.05-1.33) and 1.59 (95% CI: 1.37-1.84), respectively]. Participants with obesity also had higher risks of reporting moderate-to-severe symptoms in four Flu-PRO domains: gastrointestinal, respiratory, systemic, and throat [adjusted risk ratio (aRR) of 1.64 (95% CI: 1.01-2.70), 1.33 (95% CI: 1.05-1.67), 1.32 (95% CI: 1.06-1.63), and 1.20 (95% CI 1.02-1.40) respectively].

CONCLUSIONS

Higher BMI was associated with ILI incidence and severity. These findings prompt further research into optimal strategies to reduce the impact of ILI in MHS settings and the general population.