This case was reported in a literature article and described the occurrence of haemophilus influenzae serotype b in a 7-year-old male subject who was vaccinated with Haemophilius influenzae type b vaccine (manufacturer unspecified). The subject's medical history included chemotherapy and leukemia lymphoblastic acute at the age of 2. He was in first remission until he relapsed at the age of 4. Before this presentation, he was in remission for more than 1 year. Birth history was a term delivery with no complications and there was no significant past medical history except for ALL and a femur fracture that healed after closed reduction and casting. Surgical history included only the insertion and subsequent removal of a port-a-catch. The subject's family history was noncontributory. No recent history of nausea, vomiting, diarrhea, cough, ear pain, dysuria, malaise, confusion or syncope. No recent history of travel or camping, no known sick contacts and no known trauma. Concurrent vaccination included combined diphtheria, tetanus, pertussis (A or W not known) vaccine ;manufacturer unspecified;unknown;unknown given on an unspecified date; hepatitis B vaccine recombinant ;manufacturer unspecified;unknown;unknown given on an unspecified date; inactivated poliomyelitis virus vaccine ;manufacturer unspecified;unknown;unknown given on an unspecified date; live attenuated measles, mumps (strain not specified) , rubella vaccine ;manufacturer unspecified;unknown given on an unspecified date; measles, mumps and rubella vaccine, strain not specified ;manufacturer unspecified;unknown given on an unspecified date; varicella virus vaccine ;manufacturer unspecified;unknown;unknown given on an unspecified date. All vaccines were given more than 6 months before the diagnosis of ALL. Varicella zoster immunity was documented before initiation of chemotherapy, although anti-hib antibody testing was not performed before chemotherapy. On an unspecified date, the subject received 1st dose, 2nd dose, 3rd dose and 4th dose of Haemophilus influenzae type b vaccine (administration site and route unknown, batch number not provided). In the Summer, within years of vaccination with Haemophilus influenzae type b vaccine, the subject experienced right hip pain with weight-bearing activities. 6 days previously, he also had rise in temperature (100.2 ?F) which resolved on the same day. Since the events occurred in the Summer, there were no school or daycare exposures. Blood cultures revealed Gam-negative diplococci. The subject was hospitalised. The subject was treated with antibiotics. On physical examination, the subject was afebrile with normal vital signs. It was unremarkable except for tenderness to palpation in the right groin without warmth, swelling or erythema. The range of motion at the hip was normal, although there was discomfort with extension and abduction of the right leg. The gait was antalgic, favoring the left side. The complete blood count and manual differential were within normal limits. The urinalysis was normal and the subject's serum c-reactive protein was elevated at 7 mg/dL. An MRI of this right hip was performed which showed a large right hip joint effusion and bone marrow edema of the femoral neck that was interpreted as suspicious for osteomyelitis and septic arthritis. Arthrocentesis of the right hip and bone biopsy of the femoral neck revealed no pathologic evidence of malignancy and minimally inflammatory joint fluid. Although cultures (performed after initiation of antibiotics) were negative, osteomyelitis was presumed to be the cause of the bone marrow edema. After 6 days of improvement and a decreased of c-reactive protein, the subject was discharged to complete 10 days of IV antibiotic therapy followed by another 32 days of oral therapy. The pathogen on the initial blood cultures was identified as Haemophilus influenzae type b. Osteomyelitis was  caused by Haemophilus influenzae type b. The subject returned to clinic and titers were drawn to assess his immunity to previous vaccinations. The subject had negative serum IgG for VZV, measles, hepatitis B, tetanus, pertussis, and diphtheria, although he did still retain evidence of immunity to polio, with titers of 1:8 (polio 1), 1:64 (polio2),and1:128 (polio 3). He also had detectable Haemophilius influenzae antibodies 4 weeks after his initial presentation. Subsequent immune workup revealed normal quantitative immunoglobulins, normal lymphocyte subsets (normal CD3, CD4, CD8, and CD19, according to handbook normal values; and normal CD2, natural killer cells, CD45RA, and CD45RO according to reference laboratory standards), and normal lymphocyte proliferation in response to mitogens with absent quantitative response to tetanus antigen. A complete reimmunization schedule was undertaken with seroconversion to hepatitis B, hepatitis A, measles, VZV, pertussis, diphtheria, and tetanus. At the time of reporting, the outcome of the events was unspecified. Summary of the literature article: Acute lymphoblastic leukemia (ALL) is the most common cancer in early childhood. Protocols for both the treatment and follow-up for ALL are well established and extremely successful, with nearly an 80% 5-year incident-free survival rate. It is also well established that both ALL and the requisite chemotherapy are immunosuppressive, which makes the subject more vulnerable to pathogens usually prevented by normal childhood vaccinations. However, after treatment of ALL, once a subject is considered immunocompetent, there is currently not an accepted protocol to evaluate antibody retention from prechemotherapy vaccinations or to revaccinate ALL survivors who completed their full course of childhood vaccinations before chemotherapy. This case report describes a 7-year-old survivor of recurrent ALL who was found to have osteomyelitis caused by Haemophilus influenzae type b (Hib), for which he had been vaccinated. The subject was subsequently found to have no humoral immunologic memory to the majority of his childhood vaccinations. This case prompted an evaluation revealing a lack of humoral immunity to nearly all previous vaccinations. Recent advances in the standard chemotherapy regimen for childhood ALL have significantly improved its 5-year survival rate. However, more aggressive chemotherapy regimens can compromise patients? humoral immunity and can leave them without antibodies from previous vaccinations. The author's conclusion stated that physicians treating survivors of ALL should consider the possibility of vaccine-preventable infections in their subject population. The case presented also indicates that additional research into the immunocompetence of ALL survivors may be indicated to determine if humoral immunity testing or revaccination should be routine practice.