# The lower rate of bone and joint infection in patients with open extremity fractures associated with vaccination prior to injury: a propensity-matched cohort study

## TL;DR

This study found that patients who received vaccines before an injury had a lower risk of bone and joint infections after open fractures.

## Contribution

The study shows that prior vaccination is associated with reduced bone and joint infections in open fracture patients, possibly due to enhanced immune response.

## Key findings

- Vaccinated patients had a 2.4% BJI rate versus 12.0% in controls after open fractures.
- Vaccinated patients showed slightly higher neutrophil counts and CRP levels after injury.
- Propensity score matching confirmed balanced demographics and clinical factors between groups.

## Abstract

Vaccines could strengthen the innate immune system in addition to conferring protection against their target pathogen via vaccine-induced immunomodulation, a phenomenon termed trained immunity. The purpose of the present study was to determine whether vaccination prior to injury is associated with a lower rate of bone and joint infections (BJIs) in patients with open extremity fractures.

Patients with open extremity fractures treated at one hospital between January 2010 and December 2019 were identified. Incidental vaccine recipients and control cohorts were matched in a 1:1 ratio using propensity scores based on age, sex, anatomical location of the fracture, Gustilo–Anderson classification, body mass index (BMI), and diagnosis of diabetes. The primary endpoint was BJIs within 1 year after initial injury. Secondary outcomes were neutrophil counts and serum C-reactive protein (CRP) levels within 24 h of admission. Logistic or linear regression was performed to control for potential confounding factors when comparing primary and secondary outcomes.

Vaccine inoculation history was successfully collected from 6,338 patients, with only 83 patients receiving an incidental vaccine inoculation within 3 months before injury. After propensity score matching, demographic and clinical factors were well-balanced between cohorts (all standardized differences >0.1). After controlling for potential confounders, patients in the vaccine group were at a lower risk of BJIs after open extremity fractures (vaccine, 2/83 [2.4%]; control, 10/83 [12.0%), p = 0.011). Levels of circulating neutrophils and CRP were slightly increased in the vaccine group.

Vaccine inoculation is associated with the lower BJI rate after open extremity fractures, and vaccinated patients might have a more robust immune response against bacterial challenges in terms of neutrophil and CRP levels after injury. Future prospective cohort studies and clinical trials are warranted to evaluate this finding definitively.

http://www.chictr.org.cn/usercenter.aspx, identifier ChiCTR2000041093.