Purpose: The current study has two objectives. First, compare clinical outcomes between solid organ transplant (SOT) recipients who receive influenza vaccination and those who do not receive vaccination. Second, report the rate of influenza vaccination among SOT recipients at a large academic transplant center.

Methods: The study was a retrospective chart review of all SOT recipients receiving transplantation at our institution from January 1, 2011 to September 1, 2012. A cohort of patients who received influenza vaccination during the first full influenza season after transplant was compared to a cohort who did not receive vaccination. Each patient had outcomes collected for 1 year from the start of the first full influenza season (September 1) after transplant.

Results: The study included 586 transplant recipients with an overall vaccination rate of 59.3%. Table 1 shows the rate of vaccination for each organ. The majority of those who received vaccination did so early in the influenza season prior to December 1^st.

Baseline demographics were similar between the two groups. The rate of hospitalization per patient year was lower in the vaccinated group with 0.34 admissions per patient year versus 0.51 in the non-vaccinated group (p=0.0017). There was no difference found in the rate of admissions for pneumonia or the number of cases of influenza between the two groups. Similarly, there was no difference in the death rate per patient year between the groups.

Initially, there was no difference in the rate of rejection per patient year between those who were vaccinated and those who were not vaccinated. However, when rejection episodes that were diagnosed on the date of vaccination were removed from the vaccinated group and attributed to the non-vaccinated group, there was a significant reduction in the rejection rate per patient year as illustrated in table 2.

Conclusion: Influenza vaccination in the first year after transplant resulted in reduced rates of hospitalization across all organ types. There was no difference in rates of admissions for pneumonia, cases of influenza or mortality between the two groups. Influenza vaccination resulted in a reduction in the adjusted rate of acute rejection.

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