Safety and Immunogenicity of Live Viral Vaccines in a Multicenter Cohort of Pediatric Transplant Recipients

Vaccination strategies for solid organ transplant candidates and recipients: insights and recommendations

INTRODUCTION

Vaccines save lives. They are integral to reducing the morbidity and mortality of vaccine-preventable infections in solid organ transplant recipients. Pre-transplant vaccination provides a unique opportunity for administration of live, viral vaccines, and enhanced vaccine efficacy, compared to the post-transplant period with decreased vaccine response due to immunosuppression.

AREAS COVERED

We discuss a general approach to pre- and post-transplant vaccination in solid organ transplant candidates and recipients. We then review guideline statements and recent literature related to individual vaccines, including the recently developed respiratory syncytial virus vaccine. Travel and occupation-related vaccines are also discussed.

EXPERT OPINION

The challenge of vaccination for immunocompromised patients expands as the prevalence of immunocompromised adults rises, and immunocompromised patients are frequently excluded from vaccine trials. In an age of vaccine hesitancy and reemerging vaccine-preventable infections, well-powered, prospective studies are needed to evaluate the clinical effectiveness of vaccines in solid organ transplant candidates and recipients.

Have Live Viral Vaccine Practices Among the Pediatric Liver Transplant Community Changed? A Survey Study of Pediatric Liver Transplant Centers Across the United States

BACKGROUND

Expanded data regarding the safety and immunogenicity of live viral vaccines (LVV) during the posttransplant period has resulted in updated recommendations endorsing LVVs for select pediatric liver transplant (LT) recipients, a significant change from historical guidelines. The goal of this survey study was to understand current LVV practices among pediatric LT centers.

METHODS

A 20-question email survey detailing center-specific pre- and post-LT LVV practices was distributed between May 1, 2024, and August 1, 2024, to a representative from each US center participating in the Society of Pediatric Liver Transplantation (SPLIT).

RESULTS

The overall survey response rate was 95% (41/43 centers). In the pretransplant period, 85% of centers (35/41) administer LVVs starting at 6 months of age, 7% (3/41) wait until 9 months, and another 7% start at 12 months. The majority of centers (83%, 34/41) require a 4-week interval between LVVs and active transplant listing. In the posttransplant period, 39% of centers (16/41) never recommend LVVs, citing perceived limited safety data (63%, 10/16) and inability to reach provider consensus (31%, 5/16) as reasons. Among the 25 centers that offer LVVs, barriers faced in implementing LVV protocols include parental concerns about change from historical recommendation (48%, 12/25) and parental concerns about safety/efficacy (36%, 9/25).

CONCLUSIONS

The majority of pediatric LT centers across the US now recommend LVVs for select LT recipients. However, these centers face barriers in vaccinating all nonimmune eligible transplant recipients. Research is needed to understand and overcome barriers to widespread acceptance and implementation of evidence-based LVV recommendations.

Safety and immunogenicity of the measles-mumps-rubella vaccine in immunocompromised children with inflammatory bowel disease, or after liver transplantation: An observational study

Safety of live vaccines is questioned in children with inflammatory bowel diseases and after liver transplantation receiving immunosuppressive therapy. The objective was to monitor the immunogenicity and safety of attenuated live vaccines against measles, mumps and rubella (MMR) in children receiving immunosuppressive therapy. In this prospective multicenter observational study (DRKS00014569) 22 children and adolescents with incomplete MMR vaccination status were identified. Following individual assessment of vaccination readiness with stable immunosuppressive therapy in the last three months with no evidence of underlying disease activity, a risk-benefit assessment regarding vaccination with live-attenuated vaccines was performed. A checklist was used to assess the immune status based on thresholds for leukocyte, lymphocyte and CD4+ T cell counts, serum immunoglobulin G and M levels and detectable in vitro T cell activation. Sixteen patients were vaccinated against MMR, eleven after liver transplantation and five with inflammatory bowel disease. At the time of vaccination, four patients were receiving moderate (e.g., tacrolimus drug level below 5 ng/ml), eleven were receiving high-intensity immunosuppression (e.g. anti-tumor-necrosis factor agents, mycophenolate mofetil) and one child had previously discontinued immunosuppressive treatment. There were no serious adverse events or complications related to the vaccination. In children receiving immunosuppressive medications, the seroconversion rate for measles after the first MMR vaccination was 73.3 % (11/15) and after the second vaccination 80 % (12/15). Specific in vitro lymphocyte reactivity to measles antigen was detectable in three out of four patients after vaccination. This study shows that MMR vaccination can be carried out under immunosuppressive therapy in selected patients without relevant side effects, and a specific humoral and cellular immune response could be achieved.

Consensus statement for the diagnosis, treatment, and prognosis of kaposiform hemangioendothelioma

Kaposiform hemangioendothelioma (KHE) is a rare vascular tumor that typically presents in infancy or early childhood. As awareness of KHE increases, it is imperative that the management of KHE be updated to reflect the latest evidence-based guidelines. The aim of this study was to integrate the literature and Chinese expert opinions to provide updated recommendations that will guide the diagnosis, treatment, and prognosis of patients with KHE. According to this consensus statement, 28 nationally peer-recognized experts in vascular anomalies and an expert in evidence-based medicine were assembled and formed three consensus subgroups. A series of key themes and questions were developed for each group, including recommendations for diagnosis, treatment, and prognosis. A systematic search was conducted for English-language articles published in PubMed and other relevant studies identified by the expert panel. A diagnosis of KHE necessitates the integration of clinical, imaging, and histologic features. The treatment of KHE should be tailored to the specific characteristics of each patient, including the size of the lesion, the presence of symptoms, the location, and the overall condition of the patient. In addition to focusing on the disease itself, it is also important to consider the complications of KHE and their impact on prognosis. The recommendations presented herein are intended to assist in the guidance of clinical practice and decision-making in patients with KHE, with the objective of improving patient outcomes.

Postvaccination Immunogenicity Among Pediatric Solid Organ Transplant Recipients

This cohort study assesses the protection provided by live attenuated viral vaccines among a pediatric population of solid organ transplant recipients 1 year after vaccination.

Measles vaccination in lung transplant candidates

Background

The incidence of measles is now increasing. Measles is especially dangerous for high-risk individuals, including lung transplant candidates with severe progressive bronchopulmonary disorders.

Objective

The objective of this study was to investigate how vaccine-induced immunity is developed in lung transplant candidates seronegative for measles. In order to study vaccine-induced measles immunity, the study subjects were divided in two groups. The main group consisted of 22 patients (11 males and 11 females) with severe bronchopulmonary disorders, aged 19 to 58. The control group was made up of healthcare providers who were matched with respect to age and gender to the patients in the main group. All study subjects were given a single dose of measles vaccine. Levels of anti-measles IgG antibodies (Ab) were measured by enzyme-linked immunosorbent assay (ELISA) using the VectoMeasles-IgG kit (Russia).

Results

One month after vaccination, both study groups showed a statistically significant increase in anti-measles IgG Ab compared to baseline levels. In the main group, vaccine-induced Ab levels were significantly lower than in the control group (0.41 [0.098; 1.75] IU/mL vs. 1.94 [0.96; 3.3] IU/mL; р<0.0001). The rates of seroconversion were 73% and 100% in the main and control groups, respectively. The majority of non-responders (83%) in the main group had restrictive pulmonary disease. One year after vaccination, anti-measles Ab were detected in 36% (5/14) of the patients in the main group.

Conclusion

Administration of a single dose of measles vaccine to seronegative lung transplant candidates with severe progressive bronchopulmonary disorders was safe and resulted in protective levels of antibodies in 73% of patients. One year after vaccination, anti-measles Ab were detected in 36% of the patients, which suggested that a single dose failed to induce a robust immune response in this patient population.

Detection of viral RNA and DNA and immune response following administration of live attenuated measles and varicella vaccines in children with chronic liver disease

Infections preventable by live virus vaccines are surging in the setting of decreased herd immunity. Many children with chronic liver diseases (CLDs) are unimmunized and at increased risk for infection due to guidelines recommending against live vaccines within 4 weeks pretransplant. This prospective study of 21 children with CLD and 13 healthy controls defined the timing of measles virus and varicella-zoster virus (VZV) RNA- and DNA-emia following vaccination and compared immune responses to measles and varicella vaccines in both groups. Measles virus RNA and VZV DNA real-time PCR were measured weekly following vaccination; measles virus RNA was undetectable in all by 14 days postvaccination, but VZV DNA, which can be managed with antivirals, was detected in 1 child in the CLD group at 21 days and 1 control at 28 days postvaccination. Humoral or cell-mediated vaccine response was 100% to measles virus and 94% to VZV in the CLD group postvaccination, whereas it was 100% to both vaccines in controls. Our pilot study suggests that both live vaccines can be safely and effectively administered up to 14 days prior to transplantation in children with CLD. We anticipate this will improve vaccination rates and thus decrease rates of vaccine-preventable infections in vulnerable children with CLD.

Assessing clinical benefits of live-attenuated vaccination in post-liver transplant patients: Analysis of breakthrough infections and natural boosters

Recently, live-attenuated measles, rubella, varicella, and mumps vaccines have been administered to carefully selected post-liver transplant patients. Although attention has been focused on post-vaccination antibody titers and adverse events, the real-life clinical benefits remain unclear. A comprehensive analysis of breakthrough infections and natural boosters (asymptomatic cases with significant elevation in virus antibody titers) following immunization post-liver transplantation was conducted from 2002-2023, exploring the timing, frequency, correlation with domestic outbreaks, and degree of antibody elevation. During the median 10-year observation period among 68 post-liver transplant patients, breakthrough infections occurred only in chickenpox, with 7 mild cases (1 episode/64 person-years). A total of 59 natural booster episodes (1, 5, 20, and 33 for measles, rubella, chickenpox, and mumps, respectively) were observed, with incidence rates of 1 per 569, 110, 22, and 17 person-years, respectively. The timing of natural boosters closely correlated with domestic outbreaks (P < .05 in chickenpox and mumps), influenced by local vaccine coverage. The degree of antibody elevation was significantly higher in individuals with breakthrough infections than in those with natural boosters (P < .05). These findings suggest that immunization with live-attenuated vaccines for post-liver transplant patients has demonstrated clinical benefits. Furthermore, mass vaccination has a positive impact on post-transplant patient outcomes.

Live-attenuated vaccine failure after liver transplantation: A 20-year cohort study

BACKGROUND

A recent conditional recommendation suggests considering live-attenuated vaccines for solid organ transplant recipients, yet the conditions of their safe and effective administration remain unclear.

METHODS

This prospective study was conducted at Keio University Hospital from 2002 to August 2023. We gave a live-attenuated vaccine to liver transplant (LT) recipients fulfilling criteria for live-attenuated vaccines, including criteria for humoral and cell-mediated immunity. Patient background information, immunization date, vaccine strain, immunosuppressive agents at the time of vaccination, and antibody titers were collected. Factors related to primary and secondary vaccine failure were evaluated to enhance the effectiveness of the live-attenuated vaccine program after LT.

RESULTS

Among 67 LT recipients, 54, 55, 47, and 55 received at least one dose of live-attenuated vaccine for measles, rubella, varicella, and mumps, respectively. The difference in vaccine strains, but not the use of two or more immunosuppressive agents, was associated with a lower risk of vaccine failures. Measles vaccine with the AIK-C strain exhibited significantly lower primary and secondary failure rates than the CAM-70 strain (1/38 vs. 4/16, odds ratio: 0.08, 95 % confidence interval [CI]: 0.01-0.80, p = 0.02, and hazard ratio: 0.54, 95 % CI: 0.34-0.85, p = 0.01, respectively). No primary failures were observed with the TO-336 strain of rubella, whereas 4 of 10 LT recipients with the Matsuura strain of rubella did not seroconvert. For mumps, the Hoshino strain showed lower primary failure rates than the Torii strain (15/52 vs. 3/3, p = 0.03).

CONCLUSION

According to a 20-year long-term study, vaccine strains are the most critical factor influencing primary and secondary vaccine failure in post-transplant live-attenuated vaccination.

Long-term persistence of seroprotection against measles following measles-mumps-rubella vaccination administered before and after pediatric liver transplantation

Liver transplantation (LT) recipients are susceptible to infections, including measles. Concerns about the safety and efficacy of live-attenuated vaccines, such as the measles-mumps-rubella (MMR) vaccine, have led to hesitancy among providers in administering them to immunocompromised patients. This 9-year interventional study assessed seroprotection against measles following MMR vaccination in pediatric LT recipients. Of 119 participants enrolled, 60 (50%) were seroprotected against measles after transplantation. Among the 59 nonseroprotected participants, 56 fulfilled safety criteria and received MMR vaccination with a seroprotection rate of 90% (95% confidence interval [CI], 73%-98%) after a first dose, 95% (95% CI, 85%-99%) after primary vaccination with 1 to 3 doses, comparable to nonimmunocompromized populations. However, measles antibodies declined over time, suggesting the need for regular monitoring, and booster doses. Half of the vaccinees (26/53, 49%) subsequently lost seroprotection. Among them, 23 received additional doses of MMR, with a high seroconversion rate. At their last follow-up (median, 6.1 years; interquartile range, 3.0-8.1 after inclusion), 63% (95% CI, 49%-75%) of all vaccinees were seroprotected against measles. In conclusion, MMR vaccination in pediatric LT recipients offers seroprotection against measles, but long-term immunity should be monitored closely.

Inadvertent live vaccine administration in adult patients with inflammatory bowel disease on immunosuppressive therapy

Live vaccines are contraindicated in patients on immunosuppressive therapy. We conducted a retrospective study evaluating the administration of a live vaccine in patients with IBD on immunosuppressive therapy. The primary outcome was to determine clinical or disseminated disease episodes within three months of vaccine administration in patients who inadvertently received a live vaccine. Thirty-five patients met the inclusion criteria. Twenty-two received the measles, mumps, and varicella (MMR) vaccine, nine received the live zoster vaccine, and one received the varicella vaccine (VAR). Three patients received both the MMR and VAR. The majority of our cohort (20, 57 %) were on anti-tumor necrosis factor, followed by azathioprine (12, 34 %) and vedolizumab (3, 9 %). Although live vaccines are contraindicated in patients on immunosuppressive therapy, none of the patients in this study reported any infections after inadvertent immunization. Further studies are required to address the safety and effectiveness of live vaccine administration in this population.

Incomplete Immunity for Varicella and Measles in Pediatric Organ Transplant Candidates. Real World Experience From an Infectious Diseases Pre-Transplantation Clinic

BACKGROUND

Vaccinating pediatric solid organ transplant candidates against measles and varicella is crucial due to the risk of severe disease in immunosuppressed recipients and general avoidance of live virus vaccines post-transplantation. The world saw a resurgence of measles starting 2012 prompting the American Society of Transplantation in 2015 to release guidelines on recognition, prevention, and post-exposure prophylaxis of this disease in solid transplant recipients. This study aims to assess the extent of incomplete immunity to these viruses in candidates and the approach to immunity optimization during a period of heightened awareness.

METHODS

A cross-sectional study from 2012 to 2016 at Cleveland Clinic Children's included pediatric solid organ transplant candidates. Data on vaccination history, serology, and demographics were collected. Incomplete immunity was defined by incomplete vaccination or seronegativity.

RESULTS

Among 91 candidates, 54.9% had complete varicella vaccination. Serological varicella immunity among patients tested varied by age: < 7 years, 50.0% positive in patients with complete schedules, none in the incomplete; ≥ 7 years, 50.0% positive in patients with complete schedules, 65.5% in the incomplete. For measles, 69.2% had complete vaccination, with immunity varying by age among those tested: < 7 years, 84.6% positive in patients with complete schedules, 42.9% in the incomplete; ≥ 7 years, 81.0% with complete, 62.5% with incomplete. Only 31.1% of those who qualified for a varicella additional dose and 28% who qualified for an additional measles dose received it, respectively.

CONCLUSIONS

Incomplete immunity to varicella and measles was prevalent in pediatric solid organ transplant candidates at our center during the study period. Despite an increase in global measles activity, our efforts to optimize immunity through additional vaccine doses were only partially successful. Future research should focus on addressing strategies and understanding barriers to ensure timely vaccination for this vulnerable population prior to transplant, especially during periods of increased viral activity.

Live Vaccine and Varicella Postexposure Prophylaxis in Pediatric Liver Transplant Recipients: A Survey of Practice in Australia and New Zealand

BACKGROUND

Administration of live vaccines following liver transplant (LT) has historically not been recommended due to concerns regarding risk of vaccine-attenuated disease. However, there is evidence suggesting that in select transplant recipients live vaccinations can be administered safely. Studies in other regions have indicated that despite this evidence many clinicians remain hesitant to administer live vaccinations.

METHOD

A REDCap survey was distributed to gastroenterologists, pediatricians, and infectious diseases physicians at pediatric centers across Australia and New Zealand via email between September and November 2023. The survey included a series of questions regarding live vaccine and varicella postexposure prophylaxis (PEP) practices in pediatric LT recipients and barriers to live vaccine administration in this cohort.

RESULTS

There was a total of 16 responses to the survey, from 10 different pediatric centers, including 10/11 pediatric gastroenterology centers and all four pediatric LT centers in the region. Only 31% (5/16) of respondents (from 3/10 different centers) offer live vaccines. The main barrier to live vaccine administration was clinician reluctance and the main reason for not offering live vaccines was insufficient safety data. Sixty-nine percent (11/16) of respondents take vaccination status and/or serology into account when deciding whether to offer varicella PEP to this cohort. Respondents universally offer varicella zoster immunoglobulin as PEP, though 31% (5/16) also offer antiviral medication.

CONCLUSIONS

Many clinicians in our region remain hesitant to provide live vaccines to pediatric LT recipients, with concerns regarding insufficient safety data. Updated local guidelines may help to address this.

Varicella-Zoster Virus Pretransplant Vaccination and Posttransplant Infections Among Pediatric Solid Organ Recipients in the Two-Dose Varicella Era: A Single-Center, Multi-Organ Retrospective Study

BACKGROUND

Varicella-zoster virus (VZV) pretransplant immunization rates, exposures, and posttransplant disease are poorly characterized among pediatric solid organ transplant (SOT) recipients in the two-dose varicella vaccine era.

METHODS

A retrospective analysis of the electronic health records among children <18 years old who received SOT from January 1, 2011 through December 31, 2021, was performed at a single center to assess for missed pretransplant varicella vaccination opportunities, characterize VZV exposures, and describe posttransplant disease.

RESULTS

Among 525 children, 444 were ≥6 months old (m.o.) at SOT with a documented VZV vaccine status. Eighty-five (19%) did not receive VZV Dose One; 30 out of 85 (35%) could have been immunized. Infants 6-11 m.o. accounted for 14 out of 30 (47%) missed opportunities. Among children ≥12 m.o. with documented Dose Two status (n = 383), 72 had missed vaccination opportunities; 57 out of 72 (79%) were children 1-4 years old. Most children had unclassifiable pre-SOT serostatus as varicella serology was either not obtained/documented (n = 171) or the possibility of passive antibodies was not excluded (n = 137). Of those with classified serology (n = 188), 69 were seroimmune. Forty-seven of 525 (9%) children had recorded VZV exposures; two developed varicella-neither had documented pre-SOT seroimmunity nor had received post-exposure prophylaxis. Nine additional children had medically attended disease: four primary varicella and five zoster. Of the 11 cases, 10 had cutaneous lesions without invasive disease; one had multi-dermatomal zoster with transaminitis. Seven (64%) received treatment exclusively outpatient.

CONCLUSIONS

VZV exposure and disease still occur. Optimizing immunization among eligible candidates and ensuring patients have a defined VZV serostatus pretransplantation remain goals of care.

Live-Attenuated Vaccines in Pediatric Solid Organ Transplant

Measles, mumps, rubella (MMR), and varicella incidence rates have increased due to the delayed vaccination schedules of children secondary to the COVID-19 pandemic. Decreased herd immunity creates a risk for immunocompetent children and immunocompromised individuals in the community. Historically, live-attenuated vaccines (MMR and varicella) were recommended before solid organ transplants. The amount of time before transplant when this is appropriate is often debated, as is the utility of vaccine titers. MMR and varicella vaccines previously were not recommended in immunocompromised patients post-solid organ transplant due to the undue risk of transmission and posed infection risk. The new literature on live-attenuated vaccines in post-transplant pediatric patients provides more insight into the vaccines' safety and efficacy. The present article aims to provide guidance on live-attenuated vaccines (MMR and varicella) in the pre-transplant and post-operative solid organ transplant phases of care in pediatric patients.

Changes in graft outcomes in recipients <10 kg over 25 years of pediatric kidney transplantation in the United States

BACKGROUND

Kidney transplant (KT) was initially associated with poor outcomes, especially in smaller recipients. However, pediatric transplantation has evolved considerably over time. We investigated the impact of weight at the time of transplant and whether outcomes changed over 25 years for <10 kg recipients.

METHODS

Using the UNOS database, pediatric recipient outcomes were analyzed between 1/1/99 and 12/31/14. KT weight was stratified: <8.6 kg (mean weight of recipients <10 kg), 8.6-9.9 kg, 10-14.9 kg, 15-29.9 kg, and ≥30 kg. Outcomes in recipients <10 kg were then compared between 1990-1999 and 2000-2014.

RESULTS

17 314 pediatric KT recipients were included; 518 (3%) had a transplant weight <10 kg. The highest rates of allograft loss and death were in recipients <8.6 kg and ≥30 kg. Recipients <8.6 kg also had higher rates of delayed graft function, rejection, and longer hospital length of stay. In the multivariable Cox regression model, transplant weight was not a predictor of allograft loss. When compared with recipients <8.6 kg, patient survival hazard ratios associated with recipient weight of 10-14.9 kg, 15-29.9 kg, and ≥30 kg were 0.61 (95%CI: 0.4, 1), 0.42 (95%CI: 0.3, 0.7) and 0.32 (95%CI: 0.2, 0.6), respectively. In the later era of transplant, recipients <10 kg had improved outcomes on univariate analysis; however, the era of transplantation was not an independent predictor of allograft loss or patient survival in Cox regression models.

CONCLUSIONS

Outcomes in children weighing 8.6-9.9 kg at the time of KT were similar to higher weight groups and improved over time; however, special precautions should be taken for recipients <8.6 kg at the time of transplant.

Live-attenuated vaccination for measles, mumps, and rubella in pediatric liver transplantation

BACKGROUND

Infections are a serious short- and long-term problem after pediatric organ transplantation. In immunocompromised patients, they can lead to transplant rejection or a severe course with a sometimes fatal outcome. Vaccination is an appropriate means of reducing morbidity and mortality caused by vaccine-preventable diseases. Unfortunately, due to the disease or its course, it is not always possible to establish adequate vaccine protection against live-attenuated viral vaccines (LAVVs) prior to transplantation. LAVVs such as measles, mumps, and rubella (MMR) are still contraindicated in solid organ transplant recipients receiving immunosuppressive therapy (IST), thus creating a dilemma.

AIM

This review discusses whether, when, and how live-attenuated MMR vaccines can be administered effectively and safely to pediatric liver transplant recipients based on the available data.

MATERIAL AND METHODS

We searched PubMed for literature on live-attenuated MMR vaccination in pediatric liver transplantation (LT).

RESULTS

Nine prospective observational studies and three retrospective case series were identified in which at least 833 doses of measles vaccine were administered to 716 liver transplant children receiving IST. In these selected patients, MMR vaccination was well tolerated and no serious adverse reactions to the vaccine were observed. In addition, an immune response to the vaccine was demonstrated in patients receiving IST.

CONCLUSION

Due to inadequate vaccine protection in this high-risk group, maximum efforts must be made to ensure full immunization. MMR vaccination could also be considered for unprotected patients after LT receiving IST following an individual risk assessment, as severe harm from live vaccines after liver transplantation has been reported only very rarely. To this end, it is important to establish standardized and simple criteria for the selection of suitable patients and the administration of the MMR vaccine to ensure safe use.

Approach to vaccinating the pediatric solid organ transplant candidate and recipient

Solid organ transplantation (SOT) candidates and recipients are at increased risk for morbidity and mortality from vaccine-preventable infections. Children are at particular risk given that they may not have completed their primary immunization series at time of transplant or have acquired natural immunity to pathogens from community exposures. Multiple society guidelines exist for vaccination of SOT candidate and recipients, although challenges remain given limited safety and efficacy data available for pediatric SOT recipients, particularly for live-vaccines. After transplant, individual patient nuances regarding exposure risks and net state of immunosuppression will impact timing of immunizations. The purpose of this review is to provide readers with a concise, practical, expert-opinion on the approach to vaccinating the SOT candidate and recipient and to supplement existing guidelines. In addition, pediatric-specific knowledge gaps in the field and future research priorities will be highlighted.