Pertussis booster vaccination in HIV-infected children receiving highly active antiretroviral therapy

Type I interferons induce an epigenetically distinct memory B cell subset in chronic viral infection

Memory B cells (MBCs) are key providers of long-lived immunity against infectious disease, yet in chronic viral infection, they do not produce effective protection. How chronic viral infection disrupts MBC development and whether such changes are reversible remain unknown. Through single-cell (sc)ATAC-seq and scRNA-seq during acute versus chronic lymphocytic choriomeningitis viral infection, we identified a memory subset enriched for interferon (IFN)-stimulated genes (ISGs) during chronic infection that was distinct from the T-bet+ subset normally associated with chronic infection. Blockade of IFNAR-1 early in infection transformed the chromatin landscape of chronic MBCs, decreasing accessibility at ISG-inducing transcription factor binding motifs and inducing phenotypic changes in the dominating MBC subset, with a decrease in the ISG subset and an increase in CD11c+CD80+ cells. However, timing was critical, with MBCs resistant to intervention at 4 weeks post-infection. Together, our research identifies a key mechanism to instruct MBC identity during viral infection.

Transcriptional and Immunologic Correlates of Response to Pandemic Influenza Vaccine in Aviremic, HIV-Infected Children

People living with HIV (PWH) often exhibit poor responses to influenza vaccination despite effective combination anti-retroviral (ART) mediated viral suppression. There exists a paucity of data in identifying immune correlates of influenza vaccine response in context of HIV infection that would be useful in improving its efficacy in PWH, especially in younger individuals. Transcriptomic data were obtained by microarray from whole blood isolated from aviremic pediatric and adolescent HIV-infected individuals (4-25 yrs) given two doses of Novartis/H1N1 09 vaccine during the pandemic H1N1 influenza outbreak. Supervised clustering and gene set enrichment identified contrasts between individuals exhibiting high and low antibody responses to vaccination. High responders exhibited hemagglutination inhibition antibody titers >1:40 post-first dose and 4-fold increase over baseline. Baseline molecular profiles indicated increased gene expression in metabolic stress pathways in low responders compared to high responders. Inflammation-related and interferon-inducible gene expression pathways were higher in low responders 3 wks post-vaccination. The broad age range and developmental stage of participants in this study prompted additional analysis by age group (e.g. <13yrs and ≥13yrs). This analysis revealed differential enrichment of gene pathways before and after vaccination in the two age groups. Notably, CXCR5, a homing marker expressed on T follicular helper (Tfh) cells, was enriched in high responders (>13yrs) following vaccination which was accompanied by peripheral Tfh expansion. Our results comprise a valuable resource of immune correlates of vaccine response to pandemic influenza in HIV infected children that may be used to identify favorable targets for improved vaccine design in different age groups.

Residual immune dysfunction under antiretroviral therapy

The usage of combination antiretroviral therapy in people with HIV (PWH) has incited profound improvement in morbidity and mortality. Yet, PWH may not experience full restoration of immune function which can manifest with non-AIDS comorbidities that frequently associate with residual inflammation and can imperil quality of life or longevity. In this review, we discuss the pathogenesis underlying chronic inflammation and residual immune dysfunction in PWH, as well as potential therapeutic interventions to ameliorate them and prevent incidence or progression of non-AIDS comorbidities. Current evidence advocates that early diagnosis and prompt initiation of therapy at high CD4 counts may represent the best available approach for an improved immune recovery in PWH.

Effect of HIV exposure and timing of antiretroviral therapy initiation on immune memory responses to diphtheria, tetanus, whole cell pertussis and hepatitis B vaccines

OBJECTIVES

We evaluated memory responses and antibody persistence to diphtheria-toxoid, tetanus-toxoid, whole-cell-pertussis (DTwP), and Hepatitis-B vaccines in HIV-unexposed, HIV-exposed-uninfected and HIV-infected children previously randomized to initiate time-limited ART at 6-10 weeks (ART-Immed) or when clinically/immunologically indicated (ART-Def).

METHODS

All children received DTwP booster at 15-18 months. Antibodies were measured for pertussis-toxoid, filamentous haemagglutinin (FHA), diphtheria-toxoid, tetanus-toxoid, and hepatitis-B prior to booster, 1-2 weeks post-booster and at 24 months of age.

RESULTS

Pre-booster antibody GMC were lower in HIV-infected groups than HIV-unexposed children for all epitopes. Post-booster and at 24 months of age, the ART-Def group had lower GMCs and antibody proportion ≥0.1 IU/ml for tetanus-toxoid and diphtheria-toxoid compared to HIV-unexposed children. At 24 months of age, the ART-Immed group had higher GMCs, and more likely to maintain antibody titres ≥1.0 IU/ml to tetanus-toxoid and diphtheria-toxoid compared to HIV-unexposed children. Compared to HIV-unexposed children, at 15 and 24 months of age, persistence of antibody to HBsAg of ≥10 mIU/ml was similar in the ART-Immed group but lower among the ART-Def group. Antibody kinetics indicated more robust memory responses in HIV-exposed-uninfected than HIV-unexposed children to diphtheria-toxoid and wP.

CONCLUSION

HIV-infected children not on ART at primary vaccination had poorer memory responses, whereas HIV-exposed-uninfected children mounted robust memory responses.

Immune response to a Tdap booster in vertically HIV-infected adolescents

BACKGROUND

Pertussis cases have increased worldwide and knowledge on immune response and cytokine profile after Tdap vaccine in immunodeficient adolescents is scarce.

OBJECTIVE

To evaluate the immune response after Tdap in HIV-infected (HIV) and in healthy adolescents (CONTROL).

METHODOLOGY

Thirty HIV adolescents with CD4 cell counts >200 and 30 CONTROLs were immunized with Tdap, after a prior whole-cell DTP vaccine primary scheme. Blood samples were collected immediately before and after vaccine. Lymphocyte immunophenotyping was performed by flow cytometry; tetanus, diphtheria and pertussis toxin antibodies were assessed by ELISA; whole blood was stimulated with tetanus toxoid and Bordetella pertussis and supernatants were assessed for cytokines by xMAP.

RESULTS

Mean age of HIV and CONTROL groups were 17.9 e 17.1 years, respectively. Pain at injection site was more intense in CONTROL group. HIV group had similar increase in tetanus antibodies at 28 days (geometric mean concentration, GMC, 15.6; 95% CI, 7.52-32.4) than CONTROL group (GMC, 23.1; 95% CI, 15.0-35.5), but lower diphtheria antibodies at 28 days (GMC, 2.3; 95% CI, 0.88-6.19) than CONTROL group (GMC, 16.4; 95% CI, 10.3-26.2); for pertussis, the percentage of individuals who seroconverted was lower in HIV than CONTROL group (HIV, 62.1% versus CONTROL, 100%; p = .002). Both groups built a cellular immune response to tetanus, with a Th2 (IL-4, IL-5 and IL-13) and Th1 (IFN-γ) response, with lower cytokine levels in HIV than in CONTROL group. Especially for pertussis, cellular and humoral responses were less intense in HIV adolescents, with a lower Th1 and Th17 profile and higher IL-10 levels. HIV-infected adolescents on viral suppression showed an enhanced immune response to all the three vaccine antigens, although still at lower levels if compared to CONTROL group.

CONCLUSIONS

Both groups tolerated well and built an immune response after Tdap. However, HIV-infected adolescents would probably benefit from more frequent booster doses.

Brief Report: Seroprevalence of Pertussis Infection in HIV-Infected Adults in the United States

Pertussis is a resurgent infection that can cause significant morbidity among adults. CD4 T cells are necessary for its clearance, but pertussis studies in HIV-infected adults are limited to case reports. We analyzed stored serum samples from 299 HIV-infected adults to determine the seroprevalence of pertussis among this population. We found that 4.3% of subjects had serologic evidence of recent pertussis infection, and annual incidence of pertussis infection among subjects not vaccinated against pertussis in the last 5 years was 10.5%-17.5%. Prospective studies are needed to define the clinical presentation of pertussis in HIV-infected adults and to optimize vaccination strategies.

Immunization of children with secondary immunodeficiency

The main causes of secondary immunodeficiency at a pediatric age include infectious diseases (mainly HIV infection), malignancies, haematopoietic stem cell or solid organ transplantation and autoimmune diseases. Children with secondary immunodeficiency have an increased risk of severe infectious diseases that could be prevented by adequate vaccination coverage, but vaccines administration can be associated with reduced immune response and an increased risk of adverse reactions. The immunogenicity of inactivated and recombinant vaccines is comparable to that of healthy children at the moment of vaccination, but it undergoes a progressive decline over time, and in the absence of a booster, the patients remain at risk of developing vaccine-preventable infections. However, the administration of live attenuated viral vaccines is controversial because of the risk of the activation of vaccine viruses. A specific immunization program should be administered according to the clinical and immunological status of each of these conditions to ensure a sustained immune response without any risks to the patients' health.

Long-term effect of highly active antiretroviral therapy on immunologic features in children

BACKGROUND

Highly active antiretroviral therapy (HAART) has transformed human immunodeficiency virus infection (HIV) into a chronic condition. The effects of long-term HAART on the immune system activity of early infected children are not fully understood. Hence, the aim of this review is to investigate immune system recovery and residual alteration in HIV-infected children receiving HAART in high-income countries.

METHODS

A systematic review was performed by searches of PubMed and references of the relevant articles. Studies published between January 1, 2000 and April 1, 2014 and conducted in high-income countries reporting data on immunological features in HIV-infected children receiving HAART were included in this review.

RESULTS

Fifty-three articles were included in this review. Present knowledge on B-cell and T-cell function, immunoglobulin production, response to vaccine and innate immune system activity in HIV-infected children receiving HAART is discussed.

CONCLUSION

Starting therapy as soon as diagnosis is ascertained and monitoring vaccine response in children under HAART are the most important tools to safeguard immunological function in HIV-infected children.

Seroprevalence and vaccination coverage of vaccine-preventable diseases in perinatally HIV-1-infected patients

BACKGROUND

Even in the era of highly active antiretroviral therapy (HAART), HIV-infected subjects are at higher risk of complications from vaccine-preventable diseases than those uninfected. The current international guidelines strongly recommend that these patients should receive all the routine childhood vaccinations. Although these children represent an appropriate target for immunization, the available data indicate suboptimal coverage rates.

METHODS

To evaluate seroprotection/seropositivity rates and vaccination coverage against the common vaccine-preventable diseases, all patients with vertically transmitted HIV-1 infection who attended San Martino Hospital were enrolled. Blood samples were collected for testing antibodies against diphtheria, tetanus, hepatitis A and B viruses by Enzyme-Linked ImmunoSorbent Assay and polioviruses by microneutralization test. In order to assess immunization coverage, retrospectively was recorded the vaccination history collecting data from Regional Immunization Database.

RESULTS

A total of 39 perinatally HIV-1 infected patients were included in the study. At the time of serum was obtained, the mean age was 18,1 years (range: 6-28). The median CD4+ T-lymphocyte count was 702 cells/mm(3) (2-1476 cells/mm(3)). Twenty-nine (74.4%) patients were found with HIV RNA load < 50 copies/mL. The proportion of subjects with protective anti-tetanus and anti-HBs were 43.6% and 30.8%, respectively. Seroprotection rates about 20% against rubella and measles were found, less than 20% against all the other antigens investigated. In particular, all patients resulted susceptible to mumps. High immunization rates were observed for polio and HBV (100% and 92.3%, respectively) and suboptimal for diphtheria-tetanus (84.6%). For the other recommended vaccines the rates were generally low. None of the patients received varicella vaccine doses.

CONCLUSIONS

As in the HAART era the vertically acquired HIV infection has become a chronic treatable disease, the vaccine-induced long-term protection plays an increasingly significant role; despite good initial response to primary vaccination, subsequent decline and loss of detectable antibodies may be prevented by additional strategies for booster doses of vaccines in adolescents and young adults.

Guidelines on vaccinations in paediatric haematology and oncology patients

OBJECTIVE

Vaccinations are the most important tool to prevent infectious diseases. Chemotherapy-induced immune depression may impact the efficacy of vaccinations in children.

PATIENTS AND METHODS

A panel of experts of the supportive care working group of the Italian Association Paediatric Haematology Oncology (AIEOP) addressed this issue by guidelines on vaccinations in paediatric cancer patients. The literature published between 1980 and 2013 was reviewed.

RESULTS AND CONCLUSION

During intensive chemotherapy, vaccination turned out to be effective for hepatitis A and B, whilst vaccinations with toxoid, protein subunits, or bacterial antigens should be postponed to the less intensive phases, to achieve an adequate immune response. Apart from varicella, the administration of live-attenuated-virus vaccines is not recommended during this phase. Family members should remain on recommended vaccination schedules, including toxoid, inactivated vaccine (also poliomyelitis), and live-attenuated vaccines (varicella, measles, mumps, and rubella). By the time of completion of chemotherapy, insufficient serum antibody levels for vaccine-preventable diseases have been reported, while immunological memory appears to be preserved. Once immunological recovery is completed, usually after 6 months, response to booster or vaccination is generally good and allows patients to be protected and also to contribute to herd immunity.

Long-term immune responses to vaccination in HIV-infected patients: a systematic review and meta-analysis

Vaccine-induced antibodies may wane more quickly in persons living with human immunodeficiency virus (HIV) than in healthy individuals. We reviewed the literature on vaccines routinely recommended in HIV-infected patients to estimate how seroprotection decreases over time in those who initially responded to immunization. For each study retrieved from the literature, the decrease of seroprotection was modeled with a log binomial generalized linear model, and data were pooled in a meta-analysis to provide estimates of seroprotection 2 and 5 years after the last vaccine administration. Our analyses confirmed that the duration of seroprotection was shorter in HIV-infected patients and that with current guidelines, a substantial proportion of patients would have lost protective antibodies before a booster was proposed. We therefore discuss the implications for the monitoring of antibody levels and timing of revaccination in these patients.

2013 IDSA clinical practice guideline for vaccination of the immunocompromised host

An international panel of experts prepared an evidenced-based guideline for vaccination of immunocompromised adults and children. These guidelines are intended for use by primary care and subspecialty providers who care for immunocompromised patients. Evidence was often limited. Areas that warrant future investigation are highlighted.

Immune reconstitution and vaccination outcome in HIV-1 infected children: present knowledge and future directions

Current evidence on routine immunization of HIV-1 infected children point out the need for a special vaccine schedule in this population. However, optimal strategies for identifying individuals susceptible to infections, and then offering them sustained protection through appropriate immunization schedule, both in terms of timing and number of vaccine doses, still remain to be elucidated. Understanding the degree of immune recovery after HAART initiation is important in guiding administration of routine vaccination in HIV-1 infected children. Although quantitative measures (e.g., CD4+ T-cell counts and immunoglobulin levels) are frequently performed to evaluate immune parameters, these measures do not fully mirror functional immune recovery. Here, we will review the status of single mandatory and recommended vaccines for HIV-1 infected children in relation to immune recovery after HAART initiation with the aim of identifying new means to help design personalized vaccine schedules for this population.

Immunogenicity, immunologic memory, and safety following measles revaccination in HIV-infected children receiving highly active antiretroviral therapy

BACKGROUND

Response rates and immunologic memory following measles vaccination are reduced in human immunodeficiency virus (HIV)-infected children in the absence of highly active antiretroviral therapy (HAART).

METHODS

HIV-infected children 2 to <19 years old receiving HAART and with HIV loads <30,000 copies/mL, CD4% ≥15, and ≥1 prior measles-mumps-rubella vaccination (MMR) were given another MMR. Measles antibody concentrations before and 8, 32, and 80 weeks postvaccination were determined by plaque reduction neutralization (PRN). A subset was given another MMR 4-5 years later, and PRN antibody was measured before and 7 and 28 days later.

RESULTS

At entry, 52% of 193 subjects were seroprotected (PRN ≥120 mIU/mL). Seroprotection increased to 89% 8 weeks postvaccination, and remained at 80% 80 weeks postvaccination. Of 65 subjects revaccinated 4-5 years later, 85% demonstrated memory based on seroprotection before or 7 days after vaccination. HIV load ≤400 copies/mL at initial study vaccination was associated with higher seroprotection rates, greater antibody concentrations, and memory. Grade 3 fever or fatigue occurred in 2% of subjects.

CONCLUSIONS

Measles revaccination induced high rates of seroprotection and memory in children receiving HAART. Both endpoints were associated with HIV viral load suppression.

CLINICAL TRIALS REGISTRATION

NCT00013871 (www.clinicaltrials.gov).

Safety and immunogenicity of quadrivalent meningococcal conjugate vaccine in 2- to 10-year-old human immunodeficiency virus-infected children

BACKGROUND

Human immunodeficiency virus (HIV)-infected children are at increased risk of meningococcal infection and poor response to quadrivalent meningococcal conjugate vaccine (MCV4), but MCV4 has not been studied in preadolescent HIV-infected children.

METHODS

The P1065 trial enrolled 2- to 10-year-old HIV-infected children with CD4 ≥ 25% to receive MCV4 at entry and at week 24. Rates of response (≥ 4-fold increase in rabbit serum bactericidal antibody) against each meningococcal serogroup (A, C, Y, W-135), geometric mean titers, and rates of seroprotection (rabbit serum bactericidal antibody titer ≥ 1:128) were determined from sera obtained at entry and weeks 4, 24, 28, and 72. Adverse events were assessed for 6 weeks after each MCV4 dose.

RESULTS

At entry, 47% of the 59 participants were male, 56% black, 31% Latino, median age was 6 years, 88% were receiving antiretroviral therapy, and 75% had viral load <400 copies/mL. There were no serious adverse events within 6 weeks after MCV4 doses; all vaccination reactions were mild. Response after a single MCV4 dose was high to serogroup A (92%) and W-135 (98%); responses improved after a second dose for serogroup C (43%-80%) (P < 0.0001) and Y (76%-84%) (P = 0.38). By week 72, seroprotection rates were 93%, 91%, 78%, and 46% for serogroups W-135, Y, A, and C, respectively.

CONCLUSIONS

Two doses of MCV4 were safe and immunogenic in 2- to 10-year-old HIV-infected children. The second dose increased the proportion of children who made a response to serogroup C. Seroprotection waned substantially for serogroups A and C within 1 year of last MCV4 dose.

Immunization in special populations

In summary, immunizations in special populations require understanding the underlying disease and how it might affect the immune system's ability to mount an antibody response to vaccines or predispose certain patient populations to developing certain serious infections. There is still a great need for research on the optimal timing of vaccines after transplants, how to assess protection and development of a protective antibody response after immunization, and whether certain groups (eg, HIV) need to be revaccinated after a certain amount of time if their antibody levels decline. In addition, there are limited data on efficacy of the newer vaccines in these special patient populations, which also requires further investigation.

Vaccination in HIV-infected individuals

Vaccinations are key to limiting the increased risk of severe infectious diseases in HIV-infected patients for whom the risk–benefit ratio has been re-evaluated. Vaccine safety and immunogenicity depend on both vaccine type and immune deficiency, while vaccine-induced immune activation promotes a transient increase in viral load. Vaccine immunogenicity is reduced and wanes more rapidly, strengthening the need for revaccination. While inactivated vaccines are safe, attenuated vaccines are theoretically contraindicated, but the risk of infectious diseases outweighs the risks of severe adverse events in endemic areas, where the majority of HIV-infected individuals live, thus allowing their use when immune deficiency is moderate. Immune reconstitution with HAART has improved vaccine immune response, highlighting the importance of global access to and early initiation of therapy.

Phase I/II, open-label trial of safety and immunogenicity of meningococcal (groups A, C, Y, and W-135) polysaccharide diphtheria toxoid conjugate vaccine in human immunodeficiency virus-infected adolescents

BACKGROUND

Quadrivalent meningococcal polysaccharide conjugate vaccine (MCV4) is routinely recommended for healthy youth in the United States, but there are no data about its use in HIV-infected people.

METHODS

P1065 is a Phase I/II trial of MCV4 safety and immunogenicity in HIV-infected children and youth performed at 27 US sites of the IMPAACT network. All youth (11-24 years old) received 1 dose of open-label MCV4 at entry. Standardized questionnaires were used to evaluate safety. Baseline protective immunity was defined as rabbit serum bactericidal antibody (rSBA) titer > or = 1:128. Immunogenic response was defined as a > or = 4-fold rise in rSBA against each meningococcal serogroup. Multivariable logistic regression analysis was used to evaluate the association of demographic and clinical characteristics on immunogenic response to serogroup C.

RESULTS

Among 319 subjects who received MCV4, 10 (3.1%) reported immediate adverse events which were local and mild, and 7 (2.2%) experienced Grade > or = 3 adverse events, unrelated to vaccine. The 305 subjects with serologic data had a median age of 17 years and were 59% male, 50% Black, and 38% Latino. Subjects were stratified by entry CD4%: 12%, CD4 <15%; 40%, 15% to 24%; and 48%, > or = 25%. Baseline protective immunity varied by serogroup: A, 41%; C, 11%; W-135, 15%; Y, 35% The immunogenic response rates to serogroups A, C, W-135, and Y were 68%, 52%, 73%, and 63%, respectively. In multivariable logistic regression models, lower entry CD4%, higher entry viral load, and CDC Class B/C diagnosis were associated with significantly lower odds of response to serogroup C.

CONCLUSION

Many HIV-infected youth naturally acquire meningococcal immunity. MCV4 is safe and immunogenic in HIV-infected youth, but response rates are lower than in healthy youth, particularly for those with more advanced HIV clinical, immunologic, and virologic status.

Immunogenicity and immunologic memory after hepatitis B virus booster vaccination in HIV-infected children receiving highly active antiretroviral therapy

BACKGROUND

Hepatitis B virus (HBV) is an important cause of comorbidity in human immunodeficiency virus (HIV)-infected individuals. The immunogenicity of HBV vaccination in children receiving highly active antiretroviral therapy (HAART) was investigated.

METHODS

HIV-infected children receiving HAART who had low to moderate HIV loads and who had previously received 3 doses of HBV vaccine were given an HBV vaccine booster. Concentrations of antibody to hepatitis B surface antigen (anti-HBs) were determined before vaccination and at weeks 8, 48, and 96. A subset of subjects was administered a subsequent dose, and anti-HBs was measured before and 1 and 4 weeks later.

RESULTS

At entry, 24% of 204 subjects were seropositive. Vaccine response occurred in 46% on the basis of seropositivity 8 weeks after vaccination and in 37% on the basis of a 4-fold rise in antibody concentration. Of 69 subjects given another vaccination 4-5 years later, immunologic memory was exhibited by 45% on the basis of seropositivity 1 week after vaccination and by 29% on the basis of a 4-fold rise in antibody concentration at 1 week. Predictors of response and memory included higher nadir and current CD4 cell percentage, higher CD19 cell percentage, and undetectable HIV load.

CONCLUSIONS

HIV-infected children frequently lack protective levels of anti-HBs after previous HBV vaccination, and a significant proportion of them do not respond to booster vaccination or demonstrate memory despite receiving HAART, leaving this population insufficiently protected from infection with HBV.

Immunization and transplantation--what is new and what is coming?

Infections represent an important risk for pediatric transplant recipients. Many infections are preventable through immunization, and ongoing studies are working on increasing the number of available vaccines for these children either before or after transplantation. We examine new immunization schedules (such as pertussis vaccines in teenagers) and newly available vaccines (such as human papillomavirus vaccine), and suggest how to deliver them in pediatric transplant candidates or recipients. We also review less common vaccines (such as encephalitis vaccines), and possible vaccines of the future that could have an important clinical impact in these children, such as CMV or EBV vaccines.

Timing of HAART defines the integrity of memory B cells and the longevity of humoral responses in HIV-1 vertically-infected children

HIV-1 infection induces a progressive disruption of the B cell compartment impairing long-term immune responses to routine immunizations. Depletion of specific memory B cell pools occurs during the 1st stages of the infection and cannot be reestablished by antiretroviral treatment. We reasoned that an early control of viral replication through treatment could preserve the normal development of the memory B cell compartment and responses to routine childhood vaccines. Accordingly, we evaluated the effects of different highly-active antiretroviral therapy (HAART) schedules in 70 HIV-1 vertically-infected pediatric subjects by B cell phenotypic analyses, antigen-specific B cell enzyme-linked immunosorbent spot (ELISpot) and ELISA for common vaccination and HIV-1 antigens. Initiation of HAART within the 1st year of life permits the normal development and maintenance of the memory B cell compartment. On the contrary, memory B cells from patients treated later in time are remarkably reduced and their function is compromised regardless of viral control. A cause for concern is that both late-treated HIV-1 controllers and noncontrollers loose protective antibody titers against common vaccination antigens. Timing of HAART initiation is the major factor predicting the longevity of B cell responses in vaccinated HIV-1-infected children.

Immunization in patients with HIV infection: are practical recommendations possible?

The purpose of this article is to review immunization recommendations for HIV-infected individuals in resource-constrained countries, particularly in sub-Saharan Africa. Recent evidence suggests that HIV-infected children are at risk for low immunization coverage in sub-Saharan Africa. Routine immunization is recommended for these children. In comparison with immunocompetent children, recommendations for live-attenuated vaccines differ in HIV-infected children. However, limited laboratory capacity to diagnose HIV infection amongst young children prevents the implementation of these HIV-specific guidelines in resource-constrained countries. Re-immunization has been the focus of recent research in high- and middle-income countries. Findings show that children established on highly active antiretroviral therapy have suboptimal vaccine-specific immunity and may benefit from re-immunization. Before re-immunization guidelines can be formulated for resource-constrained countries, several questions should be addressed, including whether all HIV-infected children will benefit from routine re-immunization and what optimal number of vaccine doses should be administered. Pneumococcal and influenza infections are important causes of morbidity and mortality amongst HIV-infected individuals. There is compelling evidence showing that pneumococcal conjugate vaccines will protect HIV-infected and uninfected children against invasive infection. Pneumococcal conjugate vaccines should be prioritized for introduction in countries with high HIV prevalence. Although, annual influenza immunization is recommended for HIV-infected individuals, the effectiveness in Africa remains unclear. In conclusion, this brief overview has identified several limitations of current immunization policy and practice for HIV-infected individuals living in resource-constrained countries.