The efficacy of influenza vaccination in a pediatric oncology population

Adequate immune responses to vaccines after chemotherapy for leukaemia diagnosed in childhood

AIM

The survival rate after treatment for childhood leukaemia has greatly improved, but could result in protracted immune deficiency. This study examined the immune status of children after chemotherapy and evaluated their responses to immunisation.

METHODS

Subjects who had completed their treatment for acute lymphoblastic leukaemia at The Children's Hospital Reykjavík, Iceland, during 2011-2020 had blood drawn and were then immunised for influenza in October 2021. Blood was drawn again 4 weeks later and their humoral and cellular responses were measured with a haemagglutination inhibition assay and lymphocyte stimulation test. Antibodies to other immunisations were also evaluated.

RESULTS

We studied 18 patients (10 male) who had completed their treatment at 3.7-20.3 years of age (mean 9.1), 11-84 months (mean 36.9) before enrolment. Conventional immunological evaluation did not reveal notable abnormalities. The responses to several childhood vaccinations, including the pneumococcal conjugate vaccination, were adequate in most patients. Humoral responses to the influenza vaccine confirmed adequate reactions in all but one patient. Considerable variations were observed in the lymphocyte stimulations tests.

CONCLUSION

Most patients reacted adequately to immunisation, especially against annual influenza and Streptococcus pneumoniae, reiterating the usefulness of vaccinations. The most appropriate timing for vaccination after treatment still needs to be determined.

Lessons learnt from influenza vaccination in immunocompromised children undergoing treatment for cancer

Influenza infection contributes substantially to global morbidity and mortality, with children undergoing treatment for cancer among the most vulnerable due to immunosuppression associated with disease and treatment. However, influenza remains one of the most common vaccine-preventable diseases. Despite international guidelines recommending inactivated influenza vaccination on the basis of data supporting efficacy and an excellent safety profile in this population, uptake has often been suboptimal due to persisting hesitancy among both patients and oncologists regarding the ability of the vaccine to mount a sufficient immune response, the optimal vaccine schedule and timing, and the best method to assess response in immunocompromised populations. In this Review, we discuss the evidence regarding influenza vaccination in children with cancer, factors that influence response, and highlight strategies to optimise vaccination. Host immune factors play a substantial role, thus principles learnt from influenza vaccination can be broadly applied for the use of inactivated vaccines in children with cancer.

[Practical management during maintenance therapy of pediatric acute lymphoblastic leukemia: Recommendations of the French Society for Childhood and Adolescent Cancer and Leukemia (SFCE)]

Maintenance therapy is the last phase of treatment for acute lymphoblastic leukemia in children and adolescents. Although maintenance therapy is associated with toxicities and specific management issues, it is an essential phase of treatment that reduces the risk of relapse. The objective of this work is to propose a guide for the initiation, administration, and monitoring of maintenance therapy, and for the management of food, schooling, leisure, community life, risk of infection and links with family medicine.

Neutropenia and Infection Prophylaxis in Childhood Cancer

PURPOSE OF REVIEW

Pediatric oncology patients frequently experience episodes of prolonged neutropenia which puts them at high risk for infection with significant morbidity and mortality. Here, we review the data on infection prophylaxis with a focus on both pharmacologic and ancillary interventions. This review does not include patients receiving hematopoietic stem cell transplantation.

RECENT FINDINGS

Patients with hematologic malignancies are at highest risk for infection. Bacterial and fungal prophylaxis decrease the risk of infection in certain high-risk groups. Ancillary measures such as ethanol locks, chlorhexidine gluconate baths, GCSF, IVIG, and mandatory hospitalization do not have enough data to support routine use. There is limited data on risk of infection and role of prophylaxis in patients receiving immunotherapy and patients with solid tumors. Patients with Down syndrome and adolescent and young adult patients may benefit from additional supportive care measures and protocol modifications. Consider utilizing bacterial and fungal prophylaxis in patients with acute myeloid leukemia or relapsed acute lymphoblastic leukemia. More research is needed to evaluate other supportive care measures and the role of prophylaxis in patients receiving immunotherapy.

Vaccination of patients with haematological malignancies who did not have transplantations: guidelines from the 2017 European Conference on Infections in Leukaemia (ECIL 7)

Patients with haematological malignancies are at high risk of infection because of various mechanisms of humoral and cell-mediated immune deficiencies, which mainly depend on underlying disease and specific therapies. Some of these infections are vaccine preventable. However, these malignancies are different from each other, and the treatment approaches are diverse and rapidly evolving, so it is difficult to have a common programme for vaccination in a haematology ward. Additionally, because of insufficient training about the topic, vaccination is an area often neglected by haematologists, and influenced by cultural differences, even among health-care workers, in compliance to vaccines. Several issues are encountered when addressing vaccination in haematology: the small size of the cohorts that makes it difficult to show the clinical benefits of vaccination, the subsequent need to rely on biological parameters, their clinical pertinence not being established in immunocompromised patients, scarcity of clarity on the optimal timing of vaccination in complex treatment schedules, and the scarcity of data on long-term protection in patients receiving treatments. Moreover, the risk of vaccine-induced disease with live-attenuated vaccines strongly limits their use. Here we summarise guidelines for patients without transplantations, and address the issue by the haematological group-myeloid and lymphoid-of diseases, with a special consideration for children with acute leukaemia.

A multiyear quality improvement project to increase influenza vaccination in a pediatric oncology population undergoing active therapy

BACKGROUND

In an effort to reduce morbidity and mortality from vaccine preventable influenza infection, national consensus guidelines recommend vaccination of patients who are immunocompromised as a result of receiving cancer therapy. Quality improvement (QI) processes are a proven method used to improve vaccination rates.

PROCEDURE

We conducted a QI initiative aimed at increasing influenza vaccination in oncology patients undergoing active treatment. Primary drivers for the project focused on patient education, staff and provider education, and communication regarding vaccine-eligible patients. We performed a retrospective analysis of influenza infection among the vaccine-eligible population. This approach has validity at our institution because of the consistent follow-up and hospital admission pattern of cancer patients on active therapy such that nearly all follow-up care is delivered at our institution.

RESULTS

We successfully achieved greater than 87% vaccination of eligible patients each vaccine season (September to March). During the recommended timeframe for delivering influenza vaccine between September and December of each vaccine season, we offered the vaccine to 100% of patients on active therapy and vaccinated >90%. Barriers to success, including vaccine refusals, increased late in the vaccine season. Influenza infection was documented in 0.5-7.3% of the vaccine-eligible group.

CONCLUSION

A robust influenza vaccination program implemented using a standardized QI approach can sustain a high vaccination rate in a pediatric oncology population receiving active treatment. The influenza infection rate was under 10% in the vaccinated group.

The Effectiveness of Trivalent Inactivated Influenza Vaccine in Children with Acute Leukemia

OBJECTIVE

The objective of this study was to determine the effectiveness of trivalent inactivated influenza vaccine (TIV) for the prevention of laboratory-confirmed influenza and influenza-like illnesses (ILI) among children and adolescents receiving therapy for acute leukemia.

STUDY DESIGN

A retrospective review of the demographic and clinical characteristics of 498 patients at a pediatric cancer center who received therapy for acute leukemia during 3 successive influenza seasons (2010-2011 through 2012-2013).

RESULTS

In 498 patient seasons with a known immunization history (median age, 6 years; range, 1-21), 354 patients (71.1%) were immunized with TIV and 98 (19.7%) received a booster dose of vaccine. Vaccinated and unvaccinated patients had generally similar demographic characteristics. There were no differences in the overall rates of influenza or ILI between vaccinated and unvaccinated patients overall, or in any individual season. There was no difference in the rates of influenza or ILI between patients who received 1 dose of vaccine and those who received 2 doses. Time to first influenza infection and time to first ILI in vaccinated and unvaccinated patients were not different.

CONCLUSION

TIV did not protect children and adolescents with acute leukemia against laboratory-confirmed influenza or ILI. Future prospective studies should assess TIV effectiveness in high-risk subpopulations and alternative strategies to prevent influenza should be considered in this population.

Immunogenicity and safety of high-dose trivalent inactivated influenza vaccine compared to standard-dose vaccine in children and young adults with cancer or HIV infection

BACKGROUND

Approaches to improve the immune response of immunocompromised patients to influenza vaccination are needed.

METHODS

Children and young adults (3-21 years) with cancer or HIV infection were randomized to receive 2 doses of high-dose (HD) trivalent influenza vaccine (TIV) or of standard-dose (SD) TIV. Hemagglutination inhibition (HAI) antibody titers were measured against H1, H3, and B antigens after each dose and 9 months later. Seroconversion was defined as ≥4-fold rise in HAI titer comparing pre- and post-vaccine sera. Seroprotection was defined as a post-vaccine HAI titer ≥1:40. Reactogenicity events (RE) were solicited using a structured questionnaire 7 and 14 days after each dose of vaccine, and adverse events by medical record review for 21 days after each dose of vaccine.

RESULTS

Eighty-five participants were enrolled in the study; 27 with leukemia, 17 with solid tumor (ST), and 41 with HIV. Recipients of HD TIV had significantly greater fold increase in HAI titers to B antigen in leukemia group and to H1 antigen in ST group compared to SD TIV recipients. This increase was not documented in HIV group. There were no differences in seroconversion or seroprotection between HD TIV and SD TIV in all groups. There was no difference in the percentage of solicited RE in recipients of HD TIV (54% after dose 1 and 38% after dose 2) compared to SD TIV (40% after dose 1 and 20% after dose 2, p=0.27 and 0.09 after dose 1 and 2, respectively).

CONCLUSION

HD TIV was more immunogenic than SD TIV in children and young adults with leukemia or ST, but not with HIV. HD TIV was safe and well-tolerated in children and young adults with leukemia, ST, or HIV.

Immunogenicity and clinical effectiveness of the trivalent inactivated influenza vaccine in immunocompromised children undergoing treatment for cancer

Influenza is associated with significant morbidity and mortality in children receiving therapy for cancer, yet recommendation for, and uptake of the seasonal vaccine remains poor. One hundred children undergoing treatment for cancer were vaccinated with the trivalent inactivated influenza vaccine according to national guidelines in 2010 and 2011. Influenza‐specific hemagglutinin inhibition antibody titers were performed on blood samples taken prior to each vaccination and 4 weeks following the final vaccination. A nasopharyngeal aspirate for influenza was performed on all children who developed an influenza‐like illness. Following vaccination, seroprotection and seroconversion rates were 55 and 43% for H3N2, 61 and 43% for H1N1, and 41 and 33% for B strain, respectively. Overall, there was a significant geometric mean fold increase to H3N2 (GMFI 4.56, 95% CI 3.19–6.52, P < 0.01) and H1N1 (GMFI 4.44, 95% CI 3.19–6.19, P < 0.01) strains. Seroconversion was significantly more likely in children with solid compared with hematological malignancies and in children <10 years of age who received a two‐dose schedule compared to one. Influenza infection occurred in 2% of the vaccinated study population, compared with 6.8% in unvaccinated controls, providing an adjusted estimated vaccine effectiveness of 72% (95% CI −26–94%). There were no serious adverse events and a low reactogenicity rate of 3%. The trivalent inactivated influenza vaccine is safe, immunogenic, provides clinical protection and should be administered annually to immunosuppressed children receiving treatment for cancer. All children <10 years of age should receive a two‐dose schedule.

Quality improvement initiative to increase influenza vaccination in pediatric cancer patients

BACKGROUND

Pediatric patients with cancer face more severe complications of influenza than healthy children. Although Centers for Disease Control and Prevention guidelines recommend yearly vaccination in these patients, in our large academic center, <60% of oncology patients receiving chemotherapy were immunized at baseline. Our objective was to increase this rate through a multifaceted quality improvement initiative.

METHODS

Eligible patients were >6 months old, within 1 year of receiving chemotherapy, >100 days from stem cell transplant, and had ≥ 1 outpatient oncology visit between September 1, 2012, and March 31, 2013. Five interventions were instituted concomitantly: (1) family education: influenza/vaccine handouts were provided to families in clinic waiting rooms; (2) health informatics: daily lists of outpatients due for immunization were generated from the electronic medical record and sent automatically to triage staff and nurses; (3) outpatient clinic: patients due for vaccination were given colored wristbands during triage to alert providers; (4) inpatient: vaccine order was built into admission order set; and (5) provider education: staff education was provided at conferences on screening of patients, vaccine ordering, and documentation of refusals/contraindications.

RESULTS

The complete influenza immunization rate increased by 20.1% to 64.5%, and the proportion of patients receiving ≥ 1 dose of vaccination increased by 22.9% to 77.7%. Similar changes were noted across all cancer types, with highest rates of immunization in leukemia/lymphoma patients (86.8%) and lowest in patients after stem cell transplant (66.7%).

CONCLUSIONS

Technology, education, and multidisciplinary clinical process changes increased influenza vaccination rates. Ongoing efforts are targeting subgroups with lowest rates of immunization.

A prospective study of chemotherapy immunologic effects and predictors of humoral influenza vaccine responses in a pediatric oncology cohort

BACKGROUND

Pediatric oncology patients represent a cohort of individuals uniquely at risk of complications from influenza, yet less likely to respond to the vaccine. It is not yet clear how to best protect this vulnerable population.

METHODS

We performed a prospective analysis of 177 pediatric oncology patients to define the predictors of influenza vaccine responses. Each variable was examined over three time points and a repeated measure analysis was performed.

RESULTS

Patients with ALL vaccinated during induction phase had superior influenza vaccine responses than those subjects vaccinated during post-induction or maintenance phases (P=0·0237). Higher aggregate HAI titer responses were associated with a higher baseline B-cell count (P=0·0240), and higher CD4 and CD8 influenza-specific T-cell responses, suggesting prior antigen exposure is a significant contributor. The solid tumor cohort had equivalent responses during all time frames of chemotherapy.

DISCUSSION

The optimal protection from influenza of pediatric patients on chemotherapy should include vaccination, but it is clear that not all patients produce high titers of antibodies after vaccination. This study identified biomarkers that could be used to individualize vaccine approaches. Immunologic predictors might have a role in targeting resources, as B-cell counts predicted of vaccine responses among the patients with ALL.

Immunologic consequences of chemotherapy for ovarian cancer: impaired responses to the influenza vaccine

OBJECTIVES

To examine the effect of chemotherapy for ovarian cancer on immunologic function and to define the effect on the serologic response to the influenza vaccine.

METHODS

Under IRB approved protocols, patients with ovarian cancer were administered seasonal trivalent killed influenza vaccines. Peripheral blood was collected for immunologic assessments. Serum was analyzed for hemagglutination inhibition (HAI) antibody titers. Peripheral blood mononuclear cells were isolated to characterize T and B cell populations and function.

RESULTS

Thirty-one patients were recruited: 13 in remission receiving a dendritic cell vaccine with or without a single dose of low-dose cyclophosphamide, 3 in remission not receiving treatment, and 15 undergoing standard therapy. Significant effects on T cell and B cell subset distributions were seen. Functional effects were also seen. Few patients were able to mount a 4-fold HAI antibody response. A 4-fold response was observed for H1N1 in 20%, for H3N2 in 26%, and for influenza B in 6%. Pre-existing exposure to influenza was predictive of responders.

CONCLUSIONS

Despite CDC recommendations that patients undergoing chemotherapy receive influenza vaccine, there is little evidence to support its serologic effectiveness in this population. Patients with ovarian cancer are almost uniformly unable to mount a meaningful antibody response. These findings have serious implications for future resource allocation for both seasonal and novel pandemic influenza outbreak and understanding the immunologic deficits as a result of chemotherapy may improve patient care.

Influenza vaccination in children being treated with chemotherapy for cancer

BACKGROUND

Influenza infection is a potential cause of severe morbidity in children with cancer; therefore vaccination against influenza is recommended. However, data are conflicting regarding the immune response to influenza vaccination in children with cancer, and the value of vaccination remains unclear.

OBJECTIVES

1. To assess the efficacy of influenza vaccination in stimulating an immunological response in children with cancer during chemotherapy, compared with control groups.2. To assess the efficacy of influenza vaccination in preventing confirmed influenza and influenza-like illness and/or in stimulating immunological response in children with cancer treated with chemotherapy, compared with placebo, no intervention or different dosage schedules.3. To identify the adverse effects associated with influenza vaccines in children with cancer treated with chemotherapy, compared with other control groups.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (1966 to 2012) and EMBASE (1980 to 2012) up to August 2012. We also searched reference lists of relevant articles and conference proceedings of the Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC), the Infectious Diseases Society of America (IDSA), the Multinational Association of Supportive Care in Cancer (MASCC) and the International Society of Paediatric Oncology (SIOP).

SELECTION CRITERIA

We considered randomised controlled trials (RCTs) and controlled clinical trials (CCTs) in which the serological response to influenza vaccination of children with cancer was compared with that of control groups. We also considered RCTs and CCTs that compared the effects of influenza vaccination on clinical response and/or immunological response in children with cancer being treated with chemotherapy, compared with placebo, no intervention or different dosage schedules.

DATA COLLECTION AND ANALYSIS

Two independent review authors assessed the methodological quality of included studies and extracted the data.

MAIN RESULTS

We included 1 RCT and 9 CCTs (total number of participants = 770). None of the included studies reported clinical outcomes. All included studies reported on influenza immunity and adverse reactions to vaccination. In five studies, immune responses to influenza vaccine were compared in 272 children receiving chemotherapy and 166 children not receiving chemotherapy. In four studies, responses to influenza vaccine were assessed in 236 children receiving chemotherapy compared with responses in 142 healthy children. Measures used to assess immune responses included a four-fold rise in antibody titre after vaccination, development of a haemagglutination inhibition (HI) titre > 32 and pre- and post-vaccination geometric mean titres (GMTs). Immune responses in children receiving chemotherapy were consistently weaker (four-fold rise of 38% to 65%) than those in children who had completed chemotherapy (50% to 86%) and in healthy children (53% to 89%). In terms of adverse effects, 391 paediatric oncology patients received influenza vaccine, and the adverse effects described included mild local reactions and low-grade fever. No life-threatening or persistent adverse effects were reported.

AUTHORS' CONCLUSIONS

Paediatric oncology patients receiving chemotherapy are able to generate an immune response to the influenza vaccine, but it remains unclear whether this immune response protects them from influenza infection or its complications. We are awaiting results from well-designed RCTs addressing the clinical benefit of influenza vaccination in these patients.

Protecting pediatric oncology patients from influenza

Influenza is a common respiratory pathogen. Its severity can be unpredictable, but people with chronic illness are at increased risk of severe infection, complications, and death from influenza. This review examines evidence to support various strategies to protect pediatric oncology patients from influenza-related morbidity. Influenza vaccination should be considered standard. Additional evidence-supported measures include antiviral treatment, antiviral prophylaxis, cohorting of patients, and hospital infection control measures. Data from other high-risk populations support the vaccination of family members, double-dose or high-dose vaccination, and the use of barrier methods. These measures have the potential to optimize patient outcomes because there will be fewer treatment interruptions for acute illness. These strategies can also protect patients from prolonged hospitalizations and morbidity related to influenza.

Immunologic consequences of chemotherapy for acute myeloid leukemia

There are few data characterizing the immunologic consequences of chemotherapy for acute myeloid leukemia (AML) and almost nothing is known about the effects of chemotherapy in a pediatric AML cohort. We identified T-cell subsets, B-cell subsets, and used Enzyme-linked immunosorbent spot analyses to define the function of T cells and B cells in 7 pediatric patients with AML on chemotherapy. The data show that the effects of chemotherapy disproportionately target the B cell and depletion of B cells is associated with impaired responses to the inactivated influenza vaccine. Diminished T-cell numbers were also observed although the magnitude of the effect was less than what was seen for B cells. Furthermore, measures of T-cell function were largely intact. We conclude that humoral immunity is significantly affected by chemotherapy for AML.

Rituximab-treated patients have a poor response to influenza vaccination

The efficacy of influenza vaccination in patients treated with rituximab is a clinically important question. Rheumatology clinics are populated with patients receiving rituximab for a broad array of disorders. Although several studies have explored the efficacy of other vaccines in rituximab-treated populations, results have been conflicting. We wished to define influenza vaccine efficacy in a rituximab-treated cohort. We examined 17 evaluable subjects treated with rituximab for rheumatologic conditions. T cell subsets, B cells subsets, T cell function, and B cell function were evaluated at specific time points along with hemagglutinination inhibition titers after receiving the standard inactivated influenza vaccine. T cell subset counts were significantly different than controls but did not change with rituximab. B cells depleted in all patients but were in various stages of recovery at the time of vaccination. Influenza vaccine responsiveness was poor overall, with only 16 % of subjects having a four-fold increase in titer. Pre-existing titers were retained throughout the study, however. The ability to respond to the influenza vaccine appeared to be related to the degree of B cell recovery at the time of vaccination. This study emphasizes that antibody responses to vaccine are impaired in subjects treated with rituximab and supports the concept that B cell recovery influences influenza vaccine responsiveness.

Successful H1N1 influenza vaccination of children receiving chemotherapy for solid tumors

BACKGROUND

The hemato-oncology community has been seriously concerned about the H1N1 pandemic of 2009. Here, we report on the evaluation of the immunogenicity and tolerability of H1N1v monovalent vaccines in young patients with cancer during this pandemic.

PROCEDURE

Between December 7, 2009 and February 26, 2010, 20 children receiving chemotherapy for solid tumors at the Institute of Hematology and Pediatric Oncology of Lyon, were immunized by 2 doses of either AS03-adjuvanted or nonadjuvanted vaccine. The level of specific antibodies was assessed at D21 and D42.

RESULTS

Seroconversion was observed in 13 of the 20 cases (65%), and 18 of 20 cases (90%) had protective titers after the 2 doses. Exploratory univariate analysis failed to show a significant influence of prevaccination lymphocyte counts on seroresponse rates.

CONCLUSIONS

These data suggest that H1N1v monovalent vaccines were well tolerated by young cancer patients while on chemotherapy and achieved protective immune response in most cases.

Epidemiology and potential preventative measures for viral infections in children with malignancy and those undergoing hematopoietic cell transplantation

In pediatric patients with malignancy and those receiving hematopoietic stem cell transplants, bacterial and fungal infections have been the focus of fever and neutropenia episodes for decades. However, improved diagnostic capabilities have revealed viral pathogens as a significant cause of morbidity and mortality. Because of limited effective antiviral therapies, prevention of viral infections is paramount. Pre-exposure and post-exposure prophylaxis and antiviral suppressive therapeutic approaches are reviewed. Additionally, infection control practices specific to this patient population are discussed. A comprehensive approach utilizing each of these can be effective at reducing the negative impact of viral infections.

Influenza vaccination for immunocompromised patients: systematic review and meta-analysis from a public health policy perspective

BACKGROUND

Immunocompromised patients are vulnerable to severe or complicated influenza infection. Vaccination is widely recommended for this group. This systematic review and meta-analysis assesses influenza vaccination for immunocompromised patients in terms of preventing influenza-like illness and laboratory confirmed influenza, serological response and adverse events.

METHODOLOGY/PRINCIPAL FINDINGS

Electronic databases and grey literature were searched and records were screened against eligibility criteria. Data extraction and risk of bias assessments were performed in duplicate. Results were synthesised narratively and meta-analyses were conducted where feasible. Heterogeneity was assessed using I(2) and publication bias was assessed using Begg's funnel plot and Egger's regression test. Many of the 209 eligible studies included an unclear or high risk of bias. Meta-analyses showed a significant effect of preventing influenza-like illness (odds ratio [OR]=0.23; 95% confidence interval [CI]=0.16-0.34; p<0.001) and laboratory confirmed influenza infection (OR=0.15; 95% CI=0.03-0.63; p=0.01) through vaccinating immunocompromised patie nts compared to placebo or unvaccinated controls. We found no difference in the odds of influenza-like illness compared to vaccinated immunocompetent controls. The pooled odds of seroconversion were lower in vaccinated patients compared to immunocompetent controls for seasonal influenza A(H1N1), A(H3N2) and B. A similar trend was identified for seroprotection. Meta-analyses of seroconversion showed higher odds in vaccinated patients compared to placebo or unvaccinated controls, although this reached significance for influenza B only. Publication bias was not detected and narrative synthesis supported our findings. No consistent evidence of safety concerns was identified.

CONCLUSIONS/SIGNIFICANCE

Infection prevention and control strategies should recommend vaccinating immunocompromised patients. Potential for bias and confounding and the presence of heterogeneity mean the evidence reviewed is generally weak, although the directions of effects are consistent. Areas for further research are identified.

Immune response to 2009 pandemic H1N1 influenza virus A monovalent vaccine in children with cancer

PURPOSE

This study investigated the immune response to 2009 pandemic H1N1 influenza monovalent vaccine in children with cancer receiving chemotherapy.

METHODS

We enrolled 25 pediatric patients. Ten patients younger than 10 years old received two vaccinations and the remaining 15 patients older than 10 years old received one. We checked hemagglutination-inhibition (HAI) antibody titers in sera of patients before and 3-4 weeks after vaccination. Seroprotective titer was defined as HAI antibody titer ≥ 40 and seroresponse as ≥ 4-fold increase in HAI antibody titers after vaccination.

RESULTS

The pre- and post-vaccination seroprotective rates were 52% and 72% (P = 0.24). Sixteen (64%) patients were possibly exposed to 2009 pandemic H1N1 influenza previously, and there was significant association between possible exposure and pre-vaccination seroprotective rate (P = 0.03). Post-vaccination seroresponse rate was 32%, and seroresponse was greater in patients without pre-vaccination seroprotective titer than those with pre-vaccination seroprotective titer (50% vs. 15%, P = 0.07). Children with lymphocyte counts above 1,500/µl during vaccination period had better seroresponse than those with lymphocyte counts below 1,500/µl (P = 0.008). Post-vaccination geometric mean titer (GMT) significantly increased in patients younger than 10 years receiving two vaccinations (pre- and post-vaccination GMT were 21.4 and 60.6, respectively; P = 0.025).

CONCLUSIONS

Monovalent vaccine for the 2009 pandemic H1N1 influenza A was found to be partially immunogenic in children with cancer, as evidenced by 32% of seroresponse rate. Immune response can be improved with vaccinations administered to patients whose absolute lymphocyte counts returned to a level of 1,500/µl or higher.