Am J Transplant: Effects of influenza vaccination in solid organ transplant recipients

Background: In immunocompromised and immunocompetent people, influenza viruses are a common cause
of respiratory infections.
Influenza is a potentially serious infection in solid organ transplant (SOT) recipients that can lead to hospitalization, admission to intensive care units (ICUs), and even death
.
Annual seasonal influenza vaccination is widely recommended and is considered the primary strategy for preventing influenza and its complications in immunocompromised patients, including SOT candidates and recipients
.
The American Society of Transplantation recommends that all SOT recipients receive an annual flu vaccine
.
However, SOT recipients have been reported to be under-immune to influenza, with nearly half of SOT recipients in the United States and Europe not being vaccinated
.
Therefore, although vaccines are widely available, a significant proportion of this high-risk group is susceptible to influenza
.
Although the flu vaccine is the most widely studied vaccine among transplant recipients, its effectiveness remains controversial
.

Most studies suggest that the antibody response of SOT recipients after influenza vaccination is not optimal, and these responses depend on the immunosuppressive drug regimen used, the time since transplantation, and the type of
graft.
There are few
randomised clinical trials involving SOT recipients.
Data from a multicenter observational study of SOT recipients with laboratory-confirmed influenza infection suggest that vaccination in the same influenza season is associated with a reduction in disease severity, assessed for the onset of pneumonia and ICU admission
.
Therefore, recommendations for influenza vaccination for SOT recipients rely on immunogenicity data, observational studies, and efficacy results
from non-immunocompromised populations.

Methods: We investigated influenza vaccination coverage and effectiveness in a population-based national cohort study that included all 18-year-old ≥ receiving SOT living in Denmark between 1 December 2007 and 1 April 2016, using an improved
, season-specific approach for nine consecutive influenza seasons.
The primary outcome is the season-specific risk
of admission to hospital for pneumonia of all causes.
Secondary outcomes were season-related influenza admissions, intensive care unit (ICU) admissions, and all-cause mortality
.
The crude hazard ratio and adjusted hazard ratio (AHR) were estimated using the COX proportional hazards regression model with a 95%
confidence interval.

Results: In total, 11,381 person-years of follow-up data were collected from 5,745 people who received SOT, 48% of whom were vaccinated
.
In the same season, influenza vaccination was associated with the risk of admission for all-cause pneumonia (AHR, 0.
83; 95% CI, 0.
69-0.
99; p=.
035) and all-cause mortality (AHR, 0.
60; 95% CI, 0.
47-0.
76; p=.
001), but was associated with the risk of influenza-related admission (AHR, 0.
75; 95% CI, 0.
46-1.
22; p=.
24) or ICU admission (AHR, 0.
84; 95% CI, 0.
67-1.
06; p=14) is irrelevant
.

Table 1 Demographic characteristics of solid organ transplant recipients under influenza vaccination

Table 2 Analysis of potential comorbidities of solid organ transplant recipients based on influenza vaccination

Table 3 Socio-economic and cultural level of solid organ transplant recipients after influenza vaccination

Figure Relationship between influenza vaccination status and prognosis of solid organ transplant recipients stratified by age group
.
Rough and adjusted hazard ratios (HR) with 95% confidence intervals (95% CI)
are given.
Adjustments were made for age, transplant initiation, transplant type, education level, income, comorbidities, prescription drugs, and vaccination status

Conclusion: Despite these benefits, influenza vaccination rates among SOT recipients remain low
.
Therefore, annual flu vaccination needs to be a priority
.

Original source:

Harboe ZB, Modin D, Gustafsson F, et al.
Effect of influenza vaccination in solid organ transplant recipients: A nationwide population-based cohort study.
Am J Transplant 2022 10; 22(10)