Introduction: Infections are a common cause of morbidity and mortality among solid organ transplant recipients. Some infections are preventable with vaccination. Rates of these infections vary with immunosuppression, vaccination rates and baseline disease prevalence. Both adherence with and response to vaccination in this population are variable, and optimum vaccination strategies continue to be refined. We aimed to characterise the incidence and complications of vaccine-preventable infections in an Australian cohort of transplant recipients compared with the general population.
Methods: Eligible participants received a solid organ transplant in New South Wales, Australia, in 2000-2015. Linkage was undertaken between transplant registries and the notifiable conditions information management system. Vaccine-preventable infections were laboratory confirmed diphtheria, Haemophilus influenzae type b, influenza, invasive pneumococcal disease, measles, mumps, pertussis, poliovirus, rubella and tetanus. Extracted information included infection type, date, clinical site, hospitalizations and deaths due to infection. Crude incidence rates were calculated for each infection from transplant date censored at first infection episode, death, loss to follow up or end of observation period (Dec 2016). Standardized incidence ratios (SIR) were calculated relative to Australian population notification rates, standardizing for gender, age (5-year categories) and calendar year.
Results: Among 3,394 eligible recipients, 399 vaccine-preventable infections affected 339 (10%) recipients. Influenza was the most common vaccine-preventable infection with 352 notifications among 305 recipients. Influenza cases were much more common among transplant recipients than the general population (SIR 8.9, 95% CI 8.0-10.0, Table 1). In 36 cases (10%), hospitalization was required, and 2 deaths due to influenza were reported.

There were 20 notifications of invasive pneumococcal disease (IPD) for 18 recipients. IPD occurred 10.2 times more often among transplant recipients than the general population (95%CI: 6.4-16.2). Most (n=13, 65%) cases were hospitalized, and one patient died from invasive pneumococcal disease. The excess burden of both influenza and IPD decreased over time (Figure 1).

Cases of pertussis occurred only slightly more often than in the general population (SIR 1.5, 95%CI: 1.0-2.3). Of 26 cases, there was one reported hospitalization and no deaths due to pertussis. Only one case of mumps, and no other vaccine-preventable infections, were reported.
Conclusion: Influenza and IPD occur more frequently among organ transplant recipients than the general population, with appreciable morbidity and mortality. Excess rates of influenza and IPD have decreased over time, which may reflect improvements in vaccination. Other vaccine-preventable infections were not associated with excess disease among transplant recipients. The need for appropriate recipient vaccination is emphasized.