Waning Vaccine Immunity and Vaccination Responses in Children Treated for Acute Lymphoblastic Leukemia: A Canadian Immunization Research Network Study

Vaccinations in children with hematologic malignancies and those receiving hematopoietic stem cell transplants or cellular therapies

Children who are immune compromised are uniquely threatened by a higher risk of infections, including vaccine-preventable diseases (VPDs). Children who undergo chemotherapy or cellular therapies may not have preexisting immunity to VPDs at the time of their treatment including not yet receiving their primary vaccine series, and additionally they have higher risk of exposures (e.g., due to family structures, daycare and school setting) with decreased capacity to protect themselves using nonpharmaceutic measures (e.g., masking). In the past, efforts to revaccinate these children have often been delayed or incomplete. Treatment with chemotherapy, stem cell transplants, and/or cellular therapies impair the ability of the immune system to mount a robust vaccine response. Ideally, protection would be provided as soon as both safe and effective, which will vary by vaccine type (e.g., replicating versus nonreplicating; conjugated versus polysaccharide). While a single approach revaccination schedule following these therapies would be convenient for providers, it would not account for patient specific factors that influence the timing of immune reconstitution (IR). Evidence suggests that many of these children would mount a meaningful vaccine response as early as 3 months following completion of treatment. Here within, we provide updated guidance on how to approach vaccination both during and following completion of these therapies.

Single-Center Experience in Vaccination of Children in Special Risk Groups: A Multidisciplinary Institutional Consensus Protocol

OBJECTIVE

Despite marked improvements in the accessibility of childhood vaccines, knowledge gaps remain about the vaccination of children in special risk groups (SRG). This study aimed to analyze the clinical data of children vaccinated in SRG in a single-center unit to contribute to the clinical evidence for the specific planning of immunization of children in SRG. The second- ary aim is to present institutional consensus on the vaccination of children in SRG.

MATERIALS AND METHODS

This retrospective study was conducted at a single-center pediatric vaccination clinic. Patient charts between 2018 and 2021 were retrospectively reviewed, and clinical and laboratory data were extracted. Serial joint meetings with multiple healthcare pro- fessionals were performed to develop an institutional protocol for vaccination.

RESULTS

There were 479 children vaccinated between 2018 and 2021 for reasons such as post- chemotherapy, after hematopoietic stem cell transplantation, before/after solid organ trans- plantation, allergies, and chronic diseases. Of these, 298 (62.2%) children vaccinated in the unit due to a history of food or vaccine allergies were excluded. One hundred eighty-one children were vaccinated at a median age of 11 [7-15] years. Most children were vaccinated after treat- ment for malignancies. Solid tumors were the most frequent malignancy (67%), followed by acute lymphoblastic leukemia (29.0%) and acute myeloid leukemia (4.0%). Institutional vacci- nation protocols for cancer survivors, hematopoietic stem cells, and solid organ recipient chil- dren were developed and presented.

CONCLUSION

There is a need to prepare national guidelines for vaccinating children with altered immunocompetence. Sharing vaccination practices by multidisciplinary vaccination units might increase and provide knowledge to develop national policies.

Global caregiver perspectives on COVID-19 immunization in childhood cancer: A qualitative study

Introduction

SARS-CoV-2 has led to an unprecedented pandemic where vulnerable populations, such as those with childhood cancer, face increased risk of morbidity and mortality. COVID-19 vaccines are a critical intervention to control the pandemic and ensure patient safety. This study explores global caregiver's perspectives related to COVID-19 immunization in the context of pediatric cancer management.

Methods

A mixed methods survey was developed based on consensus questions with iterative feedback from global medical professional and caregiver groups and distributed globally to caregivers of childhood cancer via electronic and paper routes. We present qualitative findings through inductive content analysis of caregiver free-text responses.

Results

A total of 184 participants provided qualitative responses, 29.3% of total survey respondents, with a total of 271 codes applied. Codes focused on themes related to safety and effectiveness (n = 95, 35.1%), logistics (n = 69, 25.5%), statements supporting or opposing vaccination (n = 55, 20.3%), and statements discussing the limited availability of information (n = 31, 11.4%). Within the theme of safety and effectiveness, safety itself was the most commonly used code (n = 66, 24.4% of total segments and 69.5% of safety and effectiveness codes), followed by risks versus benefits (n = 18, 18.9% of safety and effectiveness codes) and efficacy (n = 11, 11.6%).

Discussion

This study provides insights to guide healthcare professionals and caregiver peers in supporting families during the complex decision-making process for COVID-19 vaccination. These findings highlight the multidimensionality of concerns and considerations of caregivers of children with cancer regarding COVID-19 vaccination and suggest that certain perspectives transcend borders and cultures.

Immune function in childhood cancer survivors: a Children's Oncology Group review

Childhood cancer and its treatment often impact the haematopoietic and lymphatic systems, with immunological consequences. Immunological assessments are not routinely included in surveillance guidelines for most survivors of childhood cancer, although a robust body of literature describes immunological outcomes, testing recommendations, and revaccination guidelines after allogeneic haematopoietic cell transplantation. Survivorship care providers might not fully consider the impaired recovery of a child's immune system after cancer treatment if the child has not undergone haematopoietic cell transplantation. We did a scoping review to collate the existing literature describing immune function after childhood cancer therapy, including both standard-dose chemotherapy and high-dose chemotherapy with haematopoietic cell rescue. This Review aims to summarise: the principles of immunology and testing of immune function; the body of literature describing immunological outcomes after childhood cancer therapy, with an emphasis on the risk of infection, when is testing indicated, and preventive strategies; and knowledge gaps and opportunities for future research.

Vaccination of immune compromised children-an overview for physicians

Immune compromised children are threatened by a higher risk of infections; some of these are preventable by vaccination. Primary care physicians play a fundamental role in optimising vaccination status. In this narrative review, we present the evidence on vaccine safety and immunogenicity in immune compromised children and discuss in which conditions live-attenuated vaccines can possibly be used. Vaccination schedules differ in some of these conditions, including the use of vaccines with higher antigenic contents (e.g. high-dose hepatitis B vaccine), additional vaccine doses (e.g. 2-dose schedule meningococcal vaccine), more frequent booster doses (e.g. life-long pneumococcal vaccine booster), supplementary vaccines (e.g. meningococcal B vaccine) and use of vaccines beyond the age of usual recommendation (e.g. Haemophilus influenza type b vaccine after 5 years of age). Serological monitoring is a useful tool for customizing vaccination schedule in immune compromised children, confirming adequate vaccine response and documenting seroprotection (especially against measles and varicella). Finally, verification of vaccination status of all household members can prevent them being vector of transmission of an infection to the immune compromised children. Conclusion: Intensified information strategies are needed to improve trust, rectify perceived risks and improve vaccine acceptability; primary physicians can play a critical role in the latter. What is Known: • Physician's awareness is key to success, since it repeatedly correlates with higher vaccination rates What is New: • The vaccination status of immunocompromised children is rarely up-to-date • Knowing the latest vaccine recommendations is challenging, as they differ for each medical condition and change periodically • This review summarises the vaccine recommendations for children with compromised immune systems and highlights how paediatricians play a key role in coordinating their application.