Long-lasting hyporesponsivenss induced by the 23-valent pneumococcal polysaccharide vaccine (PPV23) in asplenic patients with β-thalassemia major

Vaccinations in Pediatric Hematology and Oncology: Biologic Basis, Clinical Applications, and Perspectives

Children with hemato-oncological diseases represent a heterogeneous population at heightened risk for vaccine-preventable diseases. Their immunosuppressed state reduces vaccine efficacy and raises safety concerns regarding live attenuated vaccines due to the risk of viral reactivation. The immunological and clinical implications of the single conditions are significantly different; therefore, specific vaccination strategies are needed. Despite the availability of vaccine guidelines for immunocompromised patients, clinical practice remains highly variable. It is generally recommended to avoid vaccinations during chemotherapy, with some exceptions for influenza, pneumococcal, and, in some countries, hepatitis B vaccines. The timing of immune recovery after chemotherapy depends on the specific treatment and most guidelines recommend administering vaccines 3-6 months after treatment cessation. Concerning HSCT, the timing of immune recovery is affected by several factors such as the HSCT platform, graft-versus-host disease (GvHD), and infections. Inactivated vaccines are typically administered 3-6 months post-HSCT, while live attenuated vaccines are delayed for at least two years. In children with asplenia or hyposplenism, recommendations focus on immunization against encapsulated bacteria, with tailored schedules based on the patient's age and underlying condition. This paper explores the biological factors influencing vaccination efficacy and safety in pediatric hematology and oncology patients. It also provides an updated overview of the available evidence and current vaccination guidelines. Finally, this paper highlights the main clinical and research areas for further improvement to provide tailored vaccination schedules for this vulnerable population.

Evaluation of the immunization efficacy and adverse reactions of hepatitis B vaccination in children with thalassemia minor

OBJECTIVE

To assess the immunization efficacy and incidence of adverse reactions after hepatitis B vaccination in children with thalassemia based on data from real-world studies.

METHODS

A total of 625 children were recruited into this cross-sectional study. Subgroup analyses of different thalassemia types were performed using binary logistic regression, the factors affecting HBsAb levels were identified using multiple linear regression, and the dose-response relationship between the duration of immunization and seroconversion was explored using the restricted cubic spline (RCS) model to further assess the protective duration of the hepatitis B vaccine.

RESULTS

HBsAb positivity in enrolled children was 87.3% in the thalassemia group and 81.4% in the control group. Multifactorial analysis revealed that the duration of immunization, age at completion of vaccination, and whether the first dose was delayed were significant factors influencing HBsAb levels in children (P < 0.05). The threshold for HBsAb positivity may be reached when the immunization duration reaches approximately 30 months. A subgroup analysis revealed that the HBsAb positivity rate was lower in children with β-thalassemia minor compared to those with α-thalassemia minor (P = 0.001, 95% CI: 0.097 ∼ 0.536). Adverse reactions after hepatitis B vaccination were dominated by general reactions, with a statistically significant difference in injection-site redness and swelling between the thalassemia and control groups (P < 0.05).

CONCLUSIONS

The immunization response to the hepatitis B vaccine in children with thalassemia minor was comparable to healthy children, with no abnormal adverse effects seen.

British Society for Haematology guidelines to improve the care of asplenic patients: Much work done, some remaining and a call for national registries

Asplenic patients are at high risk of serious infectious or thrombotic complications, especially when they are not adequately informed of the risk and not closely followed. Ladhani et al. on behalf of the British Society for Haematology propose updated guidelines for managing these patients. Healthcare professionals need to improve infection prevention in patients with hypofunctional or absent spleen through better identification and immunisation using established national registries. Commentary on: Ladhani et al. Prevention and treatment of infection in patients with absent or hypofunctional spleen: A British Society for Haematology guideline. Br J Haematol 2024;204:1672-1686.

Prevention and treatment of infection in patients with an absent or hypofunctional spleen: A British Society for Haematology guideline

Guidelines for the prevention and treatment of infection in patients with an absent or dysfunctional spleen were published by the British Committee for Standards in Haematology in 1996 and updated in 2002 and 2011. With advances in vaccinations and changes in patterns of infection, the guidelines required updating. Key aspects included in this guideline are the identification of patients at risk of infection, patient education and information and immunisation schedules. This guideline does not address the non-infective complications of splenectomy or functional hyposplenism (FH). This replaces previous guidelines and significantly revises the recommendations related to immunisation. Patients at risk include those who have undergone surgical removal of the spleen, including partial splenectomy and splenic embolisation, and those with medical conditions that predispose to FH. Immunisations should include those against Streptococcus pneumoniae (pneumococcus), Neisseria meningitidis (meningococcus) and influenza. Haemophilus influenzae type b (Hib) is part of the infant immunisation schedule and is no longer required for older hyposplenic patients. Treatment of suspected or proven infections should be based on local protocols and consider relevant anti-microbial resistance patterns. The education of patients and their medical practitioners is essential, particularly in relation to the risk of serious infection and its prevention. Further research is required to establish the effectiveness of vaccinations in hyposplenic patients; infective episodes should be regularly audited. There is no single group ideally placed to conduct audits into complications arising from hyposplenism, highlighting a need for a national registry, as has proved very successful in Australia or alternatively, the establishment of appropriate multidisciplinary networks.

Efficacy, immunogenicity, and evidence for best-timing of pneumococcal vaccination in splenectomized adults: a systematic review

INTRODUCTION

: Streptococcus pneumoniae is the most frequent cause of overwhelming post-splenectomy infections. Pneumococcal vaccination is generally recommended for splenectomized individuals. However, most of our knowledge comes from a few observational studies or small randomized clinical trials. We conducted this systematic review to assess the evidence of efficacy, antibody response, and the best timing for pneumococcal vaccination in splenectomized individuals.

AREAS COVERED

: The systematic review was conducted according to the PRISMA guidelines. We screened 489 articles, included 21 articles, and assessed the risk of bias using Cochrane RoB 2 and ROBINS-I. We summarized the findings narratively due to the heterogeneity of the studies.

EXPERT OPINION

Splenectomized individuals seem to have adequate antibody responses to pneumococcal vaccines. No differences in antibody responses were observed compared to healthy controls, except in one study. The studies were heterogeneous, and the majority had moderate to high degree of bias. There is a lack of clinical evidence for efficacy and best timing of pneumococcal vaccination in splenectomized individuals. Randomized clinical trials addressing these issues are needed.

Preventing infections in children and adults with asplenia

An estimated 1 million people in the United States have functional or anatomic asplenia or hyposplenia. Infectious complications due to encapsulated organisms such as Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae can lead to fulminant sepsis and death, particularly in young children, in the period shortly after splenectomy, and in immunocompromised patients. Patients with asplenia are also at risk for less common infections due to Capnocytophaga, Babesia, and malaria. Antibiotic prophylaxis, vaccines, and patient and family education are the mainstays of prevention in these at-risk patients. Recommendations for antibiotic prophylaxis typically target high-risk periods, such as 1 to 3 years after splenectomy, children ≤5 years of age, or patients with concomitant immunocompromise. However, the risk for sepsis is lifelong, with infections occurring as late as 40 years after splenectomy. Currently available vaccines recommended for patients with asplenia include pneumococcal vaccines (13-valent pneumococcal conjugate vaccine followed by the 23-valent pneumococcal polysaccharide vaccine), meningococcal vaccines (meningococcal conjugate vaccines for serogroups A, C, Y and W-135 and serogroup B meningococcal vaccines), H. influenzae type b vaccines, and inactivated influenza vaccines. Ongoing booster doses are also recommended for pneumococcal and meningococcal vaccines to maintain protection. Despite the availability of prevention tools, adherence is often a challenge. Dedicated teams or clinics focused on patient education and monitoring have demonstrated substantial improvements in vaccine coverage rates for individuals with asplenia and reduced risk of infection. Future efforts to monitor the quality of care in patients with asplenia may be important to bridge the know-do gap in this high-risk population.

Perioperative Immunization for Splenectomy and the Surgeon's Responsibility: A Review

Importance

Patients who have had splenectomy have a lifelong risk of overwhelming postsplenectomy infection (OPSI), a condition associated with high mortality rates. Surgeons must be aware of the rationale of vaccination in the case of splenectomy, to provide appropriate immunization in the perioperative time.

Observations

English-language articles published from January 1, 1990, to December 31, 2019, were retrieved from MEDLINE/PubMed, Cochrane Library, and ClinicalTrials.gov databases. Randomized clinical trials as well as systematic reviews and observational studies were considered. Asplenia yields an impairment of both innate and adaptive immunity, thus increasing the risk of severe encapsulated bacterial infections. Current epidemiology of OPSI ranges from 0.1% to 8.5% but is hard to ascertain because of ongoing shifts in patients' baseline conditions and vaccine penetration. Despite the lack of randomized clinical trials, immunization appears to be effective in reducing OPSI incidence. Unfortunately, vaccination coverage is still suboptimal, with a great variability in vaccination rates being reported across institutions and time frames. Notably, current guidelines do not advocate any particular health care qualification responsible for vaccine prescription or administration. Given the dearth of high-level basic science or clinical evidence, the optimal vaccination timing and the need for booster doses are not yet well established. Although almost all guidelines indicate to not administer vaccines within 14 days before and after surgery, most data suggest that immunization might be effective even in the immediate perioperative time, thus placing the surgeon in a primary position for vaccine delivery. Furthermore, revaccination schedules are the target of ongoing debates, since a vaccine-driven hyporesponsiveness has been postulated.

Conclusions and Relevance

In patients who have undergone splenectomy, OPSI might be effectively prevented by proper immunization. Surgeons have the primary responsibility for achieving adequate, initial immunization in the setting of both planned and urgent splenectomy.

Pneumococcal Conjugate Vaccination Followed by Pneumococcal Polysaccharide Vaccination in Lung Transplant Candidates and Recipients

Background

Pneumococcal conjugate vaccination as well as pneumococcal polysaccharide vaccination are recommended for lung transplant candidates and recipients, but the combination of these vaccines has not been extensively studied in these specific populations.

Methods

Lung transplant candidates and recipients were vaccinated with a 13-valent pneumococcal conjugate vaccine, followed 8 weeks later by a pneumococcal polysaccharide vaccine. Pneumococcal antibody levels against 13 pneumococcal serotypes were measured and followed up after 1 year in the transplant recipients. These values were compared with a historical control group vaccinated with the polysaccharide vaccine alone.

Results

Twenty-five lung transplant candidates and 23 lung transplant recipients were included. For the majority of serotypes, there was no significant increase in antibody levels after additional vaccination with the polysaccharide vaccine in both patient groups. When compared with the historical control group, the antibody response in lung transplant recipients 1 year after vaccination did not seem to have improved by vaccination with both vaccines instead of the polysaccharide vaccine alone.

Conclusions

Serologic vaccination responses in lung transplant candidates and recipients were not improved by giving a 23-valent pneumococcal polysaccharide vaccine after a 13-valent pneumococcal conjugate vaccine. The benefit of this vaccination schedule in lung transplant recipients seems to differ from other immunocompromised populations. The optimal vaccination schedule for lung transplant candidates and recipients remains to be determined.

Precision immunization: a new trend in human vaccination

Vaccination has been one of the major revolutions in the history of human health. Vaccination programs have targeted entire populations such as infants or elderly subjects as a matter of being efficient with time and resources. These general populations are heterogeneous in terms of factors such as ethnicity, health status, and socio-economics. Thus, there have been variations in the safety and effectiveness profiles of certain vaccinations according to current population-wide strategies. As the concept of precision medicine has been raised in recent years, many researchers have suggested that vaccines could be administered more precisely in terms of particular target populations, vaccine formulations, regimens, and dosage levels. This review addresses the concept and framework of precision immunization, summarizes recent and representative clinical trials of among specific populations, mentions important factors to be addressed in customizing vaccinations, and provides suggestions on the establishment of precision immunization with the goal of maximizing the effectiveness of vaccines in general.

Antibody persistence 5 years after a 13-valent pneumococcal conjugate vaccine in asplenic patients with β-thalassemia: assessing the need for booster

Streptococcus pnemoniae is a major cause of morbidity and mortality among splenectomised patients with β-thalassemia major. We have previously shown that a 13-valent pneumococcal conjugate vaccine (PCV13) induces robust early immune responses in such patients, while history of repeated immunisations with the 23-valent polysaccharide pneumococcal vaccine (PPSV23) results in attenuation of the response to PCV13. However, the duration of vaccine-induced protection in splenectomised thalassemic patients and the associated need for booster immunisation remains unclear. In the current study, we enumerate antibody persistence 5 years post-PCV13 and investigate any correlation with early immune response and immunisation history. Pneumococcal serotype (PS)-specific antibodies against 5 vaccine antigens were measured 5 years post-PCV13 in 34 asplenic adults with β-thalassemia. PS-specific antibodies against 5 vaccine serotypes had declined significantly at 5 years post-PCV13 (year 5).Year 5 antibody titres remained above baseline for PS9V, 19A and19F, returned to baseline for PS23F, and dropped below baseline for PS3 (p < 0.001).Year 5 antibodies were positively correlated with day 28 antibody titres, while no correlation was found with early memory B cell response. Previous PPSV23 history was correlated with impaired antibody persistence against serotype 19A. Antibody levels dropped significantly but remained at protective levels 5 years post-PCV13.We propose that asplenic patients with β-thalassemia may benefit from measurement of antipneumococcal antibodies after 5 years post-PCV13 as they may eventually be in need for booster pneumococcal vaccination. Clinical Trials Registration ID: www.clinicaltrials.gov NCT01846923.

Effectiveness and practical uses of 23-valent pneumococcal polysaccharide vaccine in healthy and special populations

Streptococcus pneumonia (S. pneumoniae) is responsible for significant morbidity and mortality throughout the world. The 23-valent pneumococcal polysaccharide vaccines (PPV23) have been widely used for many years, but challenges are remaining in some respects, especially for its effectiveness among high-risk populations and older adults. This review aims to summarize recent clinical trials and studies of PPV23 vaccination among healthy people ≥ 2 years of age and those with high-risk conditions such as pregnant women, individuals with immunocompromising diseases and other chronic conditions, and provide health officials in China and other developing countries a comprehensive understanding of the current vaccination strategies for PPV23 and for the combined use of PPV23 and pneumococcal conjugate vaccines (PCVs) in adults.

The Asplenic Patient: Post-Insult Immunocompetence, Infection, and Vaccination

BACKGROUND

Splenic injury can occur through multiple mechanisms and may result in various degrees of residual immunocompetence. Functionally or anatomically asplenic patients are at higher risk for infection, particularly with encapsulated bacteria. Vaccination is recommended to prevent infection with these organisms; however, the recommendations are routinely updated, and vaccine selection and timing are complex.

METHODS

Review of the pertinent English-language literature, including the recommendations of the U.S. Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices.

RESULTS

Overwhelming post-splenectomy infection is associated with high morbidity and mortality rates. Patients requiring splenectomy for trauma-related injury appear to be at lower risk for infection than those undergoing splenectomy for a hematologic or oncologic indication. Initial vaccination is dependent on immunization history but generally should consist of the 13-valent pneumococcal conjugate, quadrivalent meningococcal conjugate, meningococcal serogroup B, and Haemophilus influenzae serotype b (Hib) vaccines. Antimicrobial prophylaxis for certain asplenic patients, such as children under the age of five y, may be indicated.

CONCLUSION

Immunization remains a key measure to prevent overwhelming post-splenectomy infection. Consideration of new recommendations and indications, possible interactions, and timing remains important to including optimal response to the vaccines.

Pneumococcal Vaccination in High-Risk Individuals: Are We Doing It Right?

Controversy exists regarding the optimal use of the 23-valent pneumococcal conjugate vaccine for the protection of high-risk individuals, such as children and adults with immunocompromising conditions and the elderly. The effectiveness and immunogenicity of 23-valent pneumococcal polysaccharide vaccine (PPV23) are limited in such high-risk populations compared to the healthy, with meta-analyses failing to provide robust evidence on vaccine efficacy against invasive pneumococcal disease (IPD) or pneumonia. Moreover, several studies have demonstrated a PPV23-induced state of immune tolerance or hyporesponsiveness to subsequent vaccination, where the response to revaccination does not reach the levels achieved with primary vaccination. The clinical significance of hyporesponsiveness is not yet clarified, but attenuated humoral and cellular response could lead to reduced levels of protection and increased susceptibility to pneumococcal disease. As disease epidemiology among high-risk groups shows that we are still in need of maximum serotype coverage, the optimal use of PPV23 in the context of combined conjugate/polysaccharide vaccine schedules is an important priority. In this minireview, we discuss PPV23-induced hyporesponsiveness and its implications in designing highly effective vaccination schedules for the optimal protection for high-risk individuals.