Responses to measles immunization in children infected with human immunodeficiency virus

Immunogenicity and Safety of the Measles Vaccine in HIV-Infected Children: An Updated Systematic Review

Children infected with human immunodeficiency virus (HIV) are at increased risk of measles morbidity and mortality. We searched abstracts from the PubMed, Embase, and Latin American and Caribbean Center on Health Sciences Information databases for articles published from the earliest date available through September 26, 2017. The primary outcome of interest was serological responses to measles vaccine, stratified by HIV infection status. A total of 2,858 potentially eligible articles were identified, and the final review included 12 studies published between 1992 and 2013, 9 of which reported data on vaccine safety. The studies we included represented 3,573 children, of whom at least 335 were infected with HIV, 788 were HIV-exposed but not infected, and 1,478 were unexposed to HIV. Four of the 12 studies found statistically significant reductions in seropositivity among HIV-infected children compared with HIV-uninfected children within 4 months of vaccination (prevalence ratio range, 0.44-0.70), and forest plots provided visual trends of decreasing immunity over time among HIV-infected children in 2 additional studies. No vaccine-related deaths or serious adverse events were reported. This updated review demonstrated limitations of the existing published literature but supported evidence of reduced immunogenicity of measles vaccine among HIV-infected children, supporting the World Health Organization recommendation to revaccinate HIV-infected children against measles following immune reconstitution with combination antiretroviral therapy.

Measles in adults: A comparison of hospitalised HIV-infected and HIV-uninfected patients

Background: Although measles is traditionally a childhood illness, there are an increasing number of adult cases. Despite both measles and HIV infection being endemic in sub-Saharan Africa, there are little data regarding outcomes in co-infected patients.Objectives: Compare demographic, clinical, laboratory and radiographic features, as well as outcome (length of hospital stay, complications and mortality) between HIV-infected and HIV-uninfected adult patients admitted with confirmed measles.Methods: We conducted a retrospective record review of adult patients with confirmed measles who were admitted to the Infectious Diseases Unit at the Charlotte Maxeke Johannesburg Academic Hospital during the peak of the 2009 and 2010 South African measles outbreak. The data collected included demographic, clinical and laboratory parameters, as well as outcomes.Results: Of the 33 confirmed measles cases admitted, 24 patients were tested for HIV infection and 18 tested seropositive. There were no significant differences in the demographics, clinical findings or laboratory data when comparing the HIV-positive and HIV-negative cases. Serious clinical manifestations were seen more frequently in HIV-positive patients (odds ratio [OR] 5, 95% confidence interval [CI] 0.48–51.8, p = 0.34). One of the six patients testing HIV-negative developed pneumonia, while six of the 18 HIV-positive patients had a course complicated by pneumonia. Five of these HIV-positive patients required admission to the intensive care unit, three developing respiratory failure necessitating mechanical ventilation. HIV-positive patients had several other manifestations, including acute kidney injury, purulent conjunctivitis, pancreatitis and encephalitis. HIV-positive patients had a significantly longer hospital stay (p = 0.03). There were three deaths in the HIV-positive group, but none in the HIV-negative group (OR 2.9, 95% CI 0.13–65.3, p = 0.55).Conclusion: Our study provides data on the largest series of hospitalised adults infected with HIV and co-infected with measles. More severe consequences seemed to occur in hospitalised HIV-positive patients.

Safety and Immunogenicity of Measles Vaccination in HIV-Infected and HIV-Exposed Uninfected Children: A Systematic Review and Meta-Analysis

BACKGROUND

HIV-infected and HIV-exposed uninfected (HEU) children have an increased risk of measles that may be due to altered immune responses or suboptimal timing of measles vaccination. We aimed to evaluate the safety and immunogenicity of measles vaccination in HIV-infected and HEU children.

METHODS

For this systematic review and meta-analysis, we searched PubMed, Embase, Cochrane Library, CINAHL, Global Health Library and IndMED on May 9, 2018. Studies were included if they reported on safety or seroresponse (either seroprotection/seropositivity/seroconversion) after measles vaccination in HIV-infected or HEU children. We calculated pooled estimates to compare immunogenicity outcomes between HIV-infected, HEU and HIV-unexposed children, using risk ratios [RRs] (with 95%CIs). PROSPERO registration number: CRD42017057411.

FINDINGS

Seventy-one studies met the inclusion criteria (15,363 children). Twenty-eight studies reported on safety; vaccine-associated adverse events and deaths were uncommon. Sixty-two studies reported on immunogenicity, 27 were included in the meta-analysis. HIV-infected children had lower seroresponse rates after primary vaccination compared with HIV-unexposed (RR 0.74; 95%CI: 0.61-0.90, I 2  = 85.9%) and HEU children (0.78; 0.69-0.88, I 2  = 77.1%), which was mitigated by antiretroviral therapy and time interval between vaccination and serology. HEU and HIV-unexposed children had similar seroresponses. Vaccination at 6-months resulted in similar proportions of HIV-infected children having seroresponse compared with HIV-unexposed (0.96; 0.77-1.19) and HEU children (1.00; 0.73-1.37, I 2  = 63.7%).

INTERPRETATION

Primary measles vaccination at 6-months of age may provide protection against measles during early infancy in settings with high prevalence of maternal HIV-infection, however, further studies are needed to evaluate this strategy in HEU children and HIV-infected children receiving antiretroviral therapy.

FUNDING

South African Research Chairs Initiative of the Department of Science and Technology and National Research Foundation in Vaccine Preventable Diseases; Medical Research Council: Respiratory and Meningeal Pathogens Research Unit.

Seroprevalence of transplacentally acquired measles antibodies in HIV-exposed versus HIV-unexposed infants at six months of age

BACKGROUND & OBJECTIVES

Measles infection is reported to be more severe, prolonged and associated with a higher complication rate in children with HIV infection. Reports indicate that infants born to HIV-infected women [HIV exposed infants (HEI)] may be more vulnerable to measles. The World Health Organization recommends measles vaccination starting at six months of age in these infants who may be HIV-infected themselves. However, in India, they are given measles vaccination at nine months of age like all other infants. In this study, the seroprevalence of transplacentally acquired measles antibodies was compared in HEI and unexposed infants (HUnI) at six months of age and the proportion of HEI undergoing seroconversion after immunization with measles vaccine was assessed.

METHODS

In this prospective longitudinal study, measles IgG antibodies were estimated in serum of 49 HEI and 50 HUnI aged 6-7 months. Measles vaccine was then administered to HEI. Assessment for measles IgG antibodies was repeated 8-12 wk post-immunization.

RESULTS

Measles IgG antibodies were detected in two of 49 (4.1%) HEI and 16 of 50 (32%) HUnI. HEI were 11 times more likely to lack measles antibodies as compared to HUnI (odds ratio=11.05, 95% confidence interval=2.989-40.908). Post-vaccination, seroprevalence of measles antibodies increased to 38.5 per cent (PInterpretation & conclusions: Most HEI lacked measles antibodies at six months age and were, therefore, more vulnerable to measles than HUnI. Seroconversion in response to a single dose of measles vaccine administered at six months age was low in these infants, signifying the need of additional dose(s) of measles/measles-containing vaccine.

The Reemergence of Measles

Measles, or rubeola, is a highly infectious, acute viral illness of childhood that is considered eliminated in the USA but has reemerged in the past few years. Globally, an estimated 20 million cases of measles continue to occur, and it remains a leading cause of death among young children. It is rare in the USA and other first world countries, but numerous outbreaks have occurred in the USA recently, due to a combination of factors including poor vaccine coverage and importation of cases among travelers returning from endemic areas. The diagnosis of measles is usually made clinically, when an individual presents with a constellation of symptoms including cough, coryza, conjunctivitis, high fever, and an erythematous maculopapular rash in a cephalocaudal distribution. Complications are common and include otitis media, pneumonia, encephalitis, and rarely death. A measles vaccine is available in two doses and provides excellent protection against the disease. Despite this, vaccination coverage, especially among young adults, remains poor. Given its resurgence in the USA and other countries, interventions are urgently needed to address low vaccination rates and vaccine hesitancy. Measles awareness should also be a priority among young clinicians, who may have never seen a case or are not familiar with the disease.

T cell anergy and activation are associated with suboptimal humoral responses to measles revaccination in HIV-infected children on anti-retroviral therapy in Nairobi, Kenya

HIV-infected children are less capable of mounting and maintaining protective humoral responses to vaccination against measles compared to HIV-uninfected children. This poses a public health challenge in countries with high HIV burdens. Administration of anti-retroviral therapy (ART) and revaccinating children against measles is one approach to increase measles immunity in HIV-infected children, yet it is not effective in all cases. Immune anergy and activation during HIV infection are factors that could influence responses to measles revaccination. We utilized a flow cytometry-based approach to examine whether T cell anergy and activation were associated with the maintenance of measles-specific immunoglobulin (Ig)G antibodies generated in response to measles revaccination in a cohort of HIV-infected children on ART in Nairobi, Kenya. Children who sustained measles-specific IgG for at least 1 year after revaccination displayed significantly lower programmed cell death 1 (PD-1) surface expression on CD8(+) T cells on a per-cell basis and exhibited less activated CD4(+) T cells compared to those unable to maintain detectable measles-specific antibodies. Children in both groups were similar in age and sex, CD4(+) T cell frequency, duration of ART treatment and HIV viral load at enrolment. These data suggest that aberrant T cell anergy and activation are associated with the impaired ability to sustain an antibody response to measles revaccination in HIV-infected children on ART.

Immunization of HIV infected children

Immunization is one of the most effective approaches to reduce morbidity and mortality in HIV infected children. However, progressive immune suppression may lead to impaired responsiveness to most of the vaccines. Besides this, there are many other areas of concern in these children including risk of diseases and safety issues with live vaccines, need for increased amount or number of doses of a particular vaccine, shortened duration of protective efficacy, need for revaccination after immune reconstitution and effect of vaccines on HIV viral replication. Published literature on safety, effectiveness and immunogenicity of vaccines in HIV infected children and status of individual vaccines with existing guidelines has been discussed in present review.

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).

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.

Interaction between pediatric HIV infection and measles

Infections by measles virus and by HIV cause a state of immunodeficiency in the host. While measles virus leads to a transient immunodeficiency with depression of cellular mediated immunity, natural HIV infection leads to a progressive immunodeficiency of both humoral and cellular immunity. This review will focus on the interaction between HIV and measles virus in pediatric patients. Different scenarios of virus interaction will be dissected and their implications for a practical approach in terms of the individual patient and strategies to eliminate measles virus will be discussed.

Safety and immunogenicity of early measles vaccination in children born to HIV-infected mothers in the United States: results of Pediatric AIDS Clinical Trials Group (PACTG) protocol 225

BACKGROUND.: ACTG (Pediatric AIDS Clinical Trials Group) 225, a multicenter, randomized, open-label trial in the United States evaluated reactogenicity and immunogenicity of 2 vaccination regimens: monovalent measles vaccine (Attenuvax) at 6 months of age and measles, mumps, and rubella, live attenuated (MMRII) vaccine at 12 months of age (2D), or only MMRII at 12 months of age (1D) in human immunodeficiency virus-infected (HIV-infected) (POS) and uninfected (NEG) children in the pre-highly active antiretroviral therapy (pre-HAART) period.

METHODS

Plaque-reduction neutralization (PRN) of measles-neutralizing antibody titers were evaluated at study weeks 0, 6, 26, 32, 52, and 130 (∼3 years of age).

RESULTS

The 110 subjects included: 65 2DNEG; 30 1DNEG; 7 2DPOS and 8 1DPOS. Vaccinations (n=175) were associated with no adverse experiences >Grade 2 except for Grade 3 fever (n=2, 1 1DPOS and 1 1DNEG). Six weeks after Attenuvax, all 2DPOS subjects (7/7) seroresponded (PRN titers ≥120 mIU/mL) with median titers significantly exceeding 2DNEG titers (2115 vs 628 mIU/mL, respectively; P=.023). At ∼3 years of age, 67% 1DPOS (4/6) and 83% 2DPOS (4/5) subjects maintained titers ≥120 mIU/mL. Prevaccination titers ≥25 mIU/mL among 2DNEG subjects correlated inversely with the likelihood of achieving titers ≥120 mIU/mL (56% vs 90%; P=.004).

CONCLUSIONS

Among HIV-infected children pre-HAART, Attenuvax at 6 months was well tolerated and immunogenic. These data support the current World Health Organization (WHO) recommendation to administer a first dose of measles vaccine at 6 months of age to HIV-infected children.

Correlates of protection induced by vaccination

This paper attempts to summarize current knowledge about immune responses to vaccines that correlate with protection. Although the immune system is redundant, almost all current vaccines work through antibodies in serum or on mucosa that block infection or bacteremia/viremia and thus provide a correlate of protection. The functional characteristics of antibodies, as well as quantity, are important. Antibody may be highly correlated with protection or synergistic with other functions. Immune memory is a critical correlate: effector memory for short-incubation diseases and central memory for long-incubation diseases. Cellular immunity acts to kill or suppress intracellular pathogens and may also synergize with antibody. For some vaccines, we have no true correlates, but only useful surrogates, for an unknown protective response.

A fatal case of disseminated tuberculosis coincident with measles-rubella vaccination

The authors report a fatal case of disseminated tuberculosis in a 14-yr-old girl, which developed immediately after a measles-rubella (MR) vaccination. Despite a markedly accelerated clinical course which led to death within two weeks, the authors could not identify any possible cause of the tuberculosis aggravation in this case, with the exception of the MR vaccination. The possible role that MR vaccination had on the clinical course of tuberculosis in this case is discussed.

Immune responses to measles and tetanus vaccines among Kenyan human immunodeficiency virus type 1 (HIV-1)-infected children pre- and post-highly active antiretroviral therapy and revaccination

BACKGROUND

: HIV-1-infected children have lower response rates after measles and tetanus immunization than uninfected children. We determined the extent to which highly active antiretroviral therapy (HAART) augments vaccine immunity and promotes responses to revaccination.

METHODS

: Previously immunized, antiretroviral-naive HIV-1-infected children were evaluated for immunity against measles and tetanus. After 6 months on HAART, children meeting CD4% criteria (>15%) who were persistently antibody negative were revaccinated and immunity was reassessed.

RESULTS

: At enrollment, among 90 children with mean age of 4.9 years, 67% had negative measles IgG and 22% negative tetanus IgG. Among 62 children completing 6 months on HAART, 17 (40%) of 43 without protective measles IgG converted and 10 (53%) of 19 positive children lost measles responses (P = 0.3). Children who lost responses had significantly lower measles antibody concentrations than those who remained measles IgG positive during follow-up (7.1 vs. 20.3 mg/mL; P = 0.003). Three (23%) of 13 children negative for tetanus IgG spontaneously seroconverted on HAART, while 15 (31%) of 49 children lost tetanus antibody (P = 0.008). There was a nonsignificant trend for an association between spontaneous measles seroconversion and lower baseline HIV-1 viral load (P = 0.06). Tetanus seroconversion was associated with older age (P = 0.03). After revaccination, positive responses were observed in 78% and 75% of children reimmunized against measles and tetanus, respectively.

CONCLUSIONS

: After 6 months of HAART, more than half of previously immunized children still lacked positive measles antibody. With increased use of HAART in pediatric populations, revaccination against measles and tetanus should be considered to boost response rates and immunization coverage.

Measles: old vaccines, new vaccines

Isolation of measles virus in tissue culture by Enders and colleagues in the 1960s led to the development of the first measles vaccines. An inactivated vaccine provided only short-term protection and induced poor T cell responses and antibody that did not undergo affinity maturation. The response to this vaccine primed for atypical measles, a more severe form of measles, and was withdrawn. A live attenuated virus vaccine has been highly successful in protection from measles and in elimination of endemic measles virus transmission with the use of two doses. This vaccine is administered by injection between 9 and 15 months of age. Measles control would be facilitated if infants could be immunized at a younger age, if the vaccine were thermostable, and if delivery did not require a needle and syringe. To these ends, new vaccines are under development using macaques as an animal model and various combinations of the H, F, and N viral proteins. Promising studies have been reported using DNA vaccines, subunit vaccines, and virus-vectored vaccines.

Clinical measles after measles virus challenge in simian immunodeficiency virus-infected measles virus-vaccinated rhesus monkeys

Understanding the impact of human immunodeficiency virus (HIV) infection on the clinical manifestations and kinetics of measles virus (MV) replication in MV-vaccinated and unvaccinated individuals is important for developing successful vaccine strategies for measles eradication. To model the pathogenesis of MV infection in MV-vaccinated and unvaccinated individuals infected with HIV, previously vaccinated and unvaccinated rhesus monkeys infected with simian immunodeficiency virus (SIV) were challenged with MV and monitored for clinical, virologic, and immunologic sequelae of infection. The magnitude and duration of MV viremia were unchanged by SIV infection. Nevertheless, clinical manifestations of MV infection were altered in animals with significant CD4(+) T lymphocyte loss. Importantly, 2 of the 3 SIV-infected monkeys with high titers of vaccine-induced MV-neutralizing antibody developed clinical evidence of MV infection. Thus, in this experimental animal model, a high-titer vaccine-induced MV-neutralizing antibody response does not protect against clinical manifestations of measles in the setting of a chronic acquired immunodeficiency syndrome virus infection.

HIV-infected children living in Central Africa have low persistence of antibodies to vaccines used in the Expanded Program on Immunization

Background

The Expanded Program on Immunization (EPI) is the most cost-effective measures to control vaccine-preventable diseases. Currently, the EPI schedule is similar for HIV-infected children; the introduction of antiretroviral therapy (ART) should considerably prolong their life expectancy.

Methods and Principal Findings

To evaluate the persistence of antibodies to the EPI vaccines in HIV-infected and HIV-exposed uninfected children who previously received these vaccines in routine clinical practice, we conducted a cross-sectional study of children, aged 18 to 36 months, born to HIV-infected mothers and living in Central Africa. We tested blood samples for antibodies to the combined diphtheria, tetanus, and whole-cell pertussis (DTwP), the measles and the oral polio (OPV) vaccines. We enrolled 51 HIV-infected children of whom 33 were receiving ART, and 78 HIV-uninfected children born to HIV-infected women. A lower proportion of HIV-infected children than uninfected children had antibodies to the tested antigens with the exception of the OPV types 1 and 2. This difference was substantial for the measles vaccine (20% of the HIV-infected children and 56% of the HIV-exposed uninfected children, p<0.0001). We observed a high risk of low antibody levels for all EPI vaccines, except OPV types 1 and 2, in HIV-infected children with severe immunodeficiency (CD4⁺ T cells <25%).

Conclusions and Significance

Children were examined at a time when their antibody concentrations to EPI vaccines would have still not undergone significant decay. However, we showed that the antibody concentrations were lowered in HIV-infected children. Moreover, antibody concentration after a single dose of the measles vaccine was substantially lower than expected, particularly low in HIV-infected children with low CD4⁺ T cell counts. This study supports the need for a second dose of the measles vaccine and for a booster dose of the DTwP and OPV vaccines to maintain the antibody concentrations in HIV-infected and HIV-exposed uninfected children.

Response to Measles, Mumps, and Rubella Revaccination in HIV-Infected Children with Immune Recovery after Highly Active Antiretroviral Therapy

BACKGROUND

The low prevalence of measles antibody in human immunodeficiency virus (HIV)-infected children after immune recovery as a result of highly active antiretroviral therapy increases the risk of morbidity and mortality from disease. The objective of our study was to evaluate the efficacy and safety of revaccination with measles, mumps, and rubella (MMR) vaccine in HIV-infected children with immune recovery.

METHODS

Inclusion criteria were (1) HIV-infected children aged >5 years, (2) a nadir CD4 lymphocyte percentage <or=15%, (3) immune recovery (defined as a CD4 lymphocyte percentage >15% for >or=3 months after highly active antiretroviral therapy), and (4) no protective antibody against measles. Each child received 1 dose of MMR vaccine, and antibodies were measured at 4 and 24 weeks after vaccination. Protective antibodies were defined as an antimeasles immunoglobulin G (IgG) level >or=320 mIU/mL, an antimumps IgG titer >1:500, and an antirubella IgG level >10 IU/mL.

RESULTS

There were 51 participants. The mean age (+/- standard deviation) was 10.2 +/- 2.5 years. Prior to revaccination, 28 participants (55%) had baseline protective antibody to mumps, and 11 (20%) had baseline protective antibody to rubella. The prevalence of protective antibody at 4 weeks was 90%, 100%, and 78% for measles, rubella, and mumps, respectively, and then slightly decreased to 80%, 94%, and 61%, respectively, at 24 weeks after revaccination. No serious adverse reactions were attributed to revaccination.

CONCLUSIONS

The majority of HIV-infected children with immune recovery can develop protective antibodies after MMR revaccination. Revaccination with MMR vaccine in HIV-infected children with immune recovery should be considered to ensure individual immunity and limit the spread of disease.

Prevalence of protective antibody against measles in HIV-infected children with immune recovery after highly active antiretroviral therapy

OBJECTIVES

This study was conducted to determine the prevalence of measles-protective antibody in HIV-infected children with immune recovery after highly active antiretroviral therapy (HAART).

METHODS

Ninety-six HIV-infected children were enrolled in the study. Their mean age was 9.7+/-2.6 years, 47% were boys, and 47% were in Centers for Disease Control and Prevention (CDC) clinical category C. All participants had been treated with HAART until they achieved a CD4 cell percentage > or =15%. Three children with a history of clinical measles infection were not included in the data analysis.

RESULTS

Only 39 out of 93 children (42%) had a measles-protective antibody level, defined as an anti-measles immunoglobulin G (IgG) level > or =320 mIU/mL. There was no significant difference between the groups with and without protective levels of measles antibody in gender, clinical category, age at which HAART was started, duration of severe immune suppression, CD4 cell count and percentage, or plasma HIV RNA level before and after HAART.

CONCLUSIONS

We conclude that, despite a history of measles immunization and evidence of immune reconstitution after HAART, many healthy HIV-infected children are still susceptible to measles.

Improvements in immunization compliance using a computerized tracking system for inner city clinics

Vaccination compliance rates were calculated for 1995 to 2001 for enrolled patients, based on the Centers for Disease Control and Prevention guidelines and age-appropriate vaccine schedules. The results reported here indicate computerized tracking with the Doctor's Pediatric Immunization Program (Dr. PIP) maintained vaccine compliance rates (> 90%) in healthy and immunocompromised children at 2 months and 12 months of age. Instituting the computerized system has yielded nearly optimal results in both indigenous inner-city clinics. Despite the efficient progress made by automated tracking, the results for specific vaccine strategies (Varicella) and target groups (human immunodeficiency virus, high-risk indigent populations) may require on-going and intensive educational efforts to achieve optimization levels.

Vaccines for viral diseases with dermatologic manifestations

Vaccines against infectious diseases have been available since the 1800s, when an immunization strategy against smallpox developed by Jenner gained wide acceptance. Until recently, the only vaccination strategies available involved the use of protein-based, whole killed, and attenuated live virus vaccines. These strategies have led to the development of effective vaccines against a variety of diseases with primary or prominent cutaneous manifestations. Effective and safe vaccines now used worldwide include those directed against measles and rubella (now commonly used together with a mumps vaccine as the trivalent MMR), chickenpox, and hepatitis B. The eradication of naturally occurring smallpox remains one of the greatest successes in the history of modern medicine, but stockpiles of live smallpox exist in the United States and Russia. Renewed interest in the smallpox vaccine reflects concerns about a possible bioterrorist threat using this virus. Yellow fever is a hemorrhagic virus endemic to tropical areas of South America and Africa. An effective vaccine for this virus has existed since 1937, and it is used widely in endemic areas of South America, and to a lesser extent in Africa. This vaccine is recommended once every 10 years for people who are traveling to endemic areas. Advances in immunology have led to a greater understanding of immune system function in viral diseases. Progress in genetics and molecular biology has allowed researchers to design vaccines with novel mechanisms of action (eg, DNA, vector, and VLP vaccines). Vaccines have also been designed to specifically target particular viral components, allowing for stimulation of various arms of the immune system as desired. Ongoing research shows promise in prophylactic and therapeutic vaccination for viral infections with cutaneous manifestations. Further studies are necessary before vaccines for HSV, HPV, and HIV become commercially available.

Prospective study of measles in hospitalized, human immunodeficiency virus (HIV)-infected and HIV-uninfected children in Zambia

Measles in persons coinfected with human immunodeficiency virus (HIV) has been reported to be unusual in its presentation and frequently fatal. To determine the effect of HIV coinfection on the clinical features and outcome of measles, a prospective study of hospitalized children with measles was conducted between January 1998 and October 2000 in Lusaka, Zambia. One-sixth (17%) of 546 children hospitalized with laboratory-confirmed measles were coinfected with HIV. One-third of the HIV-infected children hospitalized with confirmed measles were <9 months old, compared with 23% of HIV-uninfected children (P=.03). Few differences in clinical manifestations, complications, or mortality were found between HIV-infected and HIV-uninfected children with measles. HIV-infected children constitute a significant proportion of children hospitalized with measles in countries with high HIV prevalence and are more likely to be younger than the age for routine measles immunization.

Abnormal CD40 ligand (CD154) expression in human immunodeficiency virus-infected children

The CD40 ligand (CD154), expressed primarily on activated CD4-positive T cells, is a costimulatory molecule involved in B-cell proliferation, germinal center formation, and immunoglobulin class switching. Since B-cell abnormalities including hypergammaglobulinemia and abnormal antibody-specific immune responses are prominent and occur early during the course of pediatric human immunodeficiency virus (HIV) infection, we measured the baseline levels and the induced levels of expression of CD154 on CD3(+) CD8(-) (T helper cells) in HIV-infected children and uninfected children born to HIV-positive mothers. The percentage of CD154(+) T helper cells activated in vitro and the level of CD154 expressed per T helper cell (mean fluorescent channel [MFC]) were significantly lower in the HIV-infected children than in the uninfected control group (77% +/- 3% versus 89% +/- 1%, respectively [P < 0.002], and 261 +/- 174 versus 415 +/- 130 MFC, respectively [P < 0.03]). The levels of CD154 expressed on resting T helper cells in the HIV-infected group were not significantly different from the levels observed in the control group. In the HIV-infected children, the level of CD154 on activated T helper cells correlated with the level of immunodeficiency, as assessed by the CD4 T-cell levels (correlation coefficient [r] = 0.707, P = 0.003), but did not correlate with the viral load or with any of the serum immunoglobulin concentrations measured in this group of HIV-infected children. The baseline level of CD154 expressed on T helper cells did, however, correlate with the concentration of immunoglobulin A in serum. We conclude that HIV-infected children have impaired regulation of CD154 expression which may contribute to the immune dysregulation commonly observed.

Travel-related vaccines

Travelers are at increased risk for several infections, including familiar infections such as measles that are widely distributed but more common in developing countries. Vaccines can markedly decrease the risk for many of these infections and are an important part of pretravel preparation. Travel provides an opportunity to review and update routine vaccines in adults and assess risk from unusual infections. Global travel is growing. Persons who are elderly, HIV-infected, and immunocompromised account for many of the travelers. Studies that assess the immunogenicity, efficacy, and adverse effects of some of the special vaccines used primarily in travelers generally have been done in young, healthy populations. Findings in young adults do not apply to other populations in whom immune response can be slower, less effective, and less durable. Recent reports of severe adverse events in elderly persons who have received yellow fever vaccine are a reminder that widely used, old vaccines can have unexpected side effects when used in a new population. It is biologically plausible that adverse effects might be more common in the elderly, and epidemiologically plausible that occasional instances of similar adverse events in the past could have been missed. Studies on special and travel vaccines in the elderly are needed urgently to define how these vaccines should be used in older populations and whether alternative means for protection are needed.

Immunologic correlates of protection induced by vaccination

Vaccine design and licensing depend on the choice of protective antigens and the demonstration of their efficacy. Ideally efficacy correlates with some measurement of immune response, although occasionally the correlation is weak and in the case of some vaccines uncertain. This paper attempts to review what is known about correlates of vaccine-induced protection. Although mucosal and cellular immune responses are clearly important to protection by some vaccines, most vaccines licensed today depend for their efficacy on serum antibodies. Particular levels of antibodies can be identified that confer protection most of the time. A condition for the efficacy of antibodies is functionality, i.e. their ability to kill or inactivate pathogens. The immune system is redundant, and the different types of responses to vaccines act synergistically.

Opportunistic infections and other clinical manifestations of HIV disease in children

As the decade draws to a close, physicians can be cautiously optimistic about the prevention and treatment of opportunistic infections in children with HIV disease. As more children receive therapy with powerful antiretroviral regimens, fewer are likely to be at risk for opportunistic pathogens. The widespread use of protease inhibitor combination therapies has already resulted in a dramatic decrease in morbidity and mortality in the population of HIV-infected adults. The same effect has been seen at pediatric care centers throughout the United States. Clinicians caring for HIV-infected children are now considering the safety of discontinuing prophylactic therapies for children with sustained immunologic improvement on antiretroviral therapy. For children who remain at risk, prophylactic regimens for PCP and MAC have been shown to decrease the risk for these infections. Preventive regimens for several other opportunistic infections are also available. The understanding of the pathogenesis of HIV and many of the opportunistic pathogens has led to the development of a variety of efficacious therapies for these infections. Despite these advances, physicians can anticipate that HIV-infected children will continue to develop opportunistic infections and other related complications. Some children fail to respond to antiretroviral therapies, whereas others are unable to tolerate the complex medication regimens. Prophylactic therapies are not 100% protective and, despite improved treatments, few opportunistic infections are cured. Most require lifelong maintenance therapy in the absence of immune reconstitution. Drug interactions, complex dosing schedules, adverse side effects, and high costs further limit the efficacy of these therapies. The prophylaxis, diagnosis, and treatment of opportunistic infections are likely to remain integral components of HIV care for the near and distant future.

Vaccination and HIV: a review of the literature

People with HIV are at risk for a variety of infections both at home and abroad. Recent studies have reported conflicting data concerning potential harmful effects following several inactivated vaccines. Antigenic stimulation by vaccines designed to prevent secondary infections may promote HIV-1 replication in certain patients. In HIV-positive subjects, immune response worsens with progression of the HIV infection. When vaccination is considered, administration of the vaccine must be performed as early as possible in the course of HIV infection because an HIV-infected patient's response to inactivated vaccines is closely related to HIV infection stage. A minority of subjects have a protective antibody response to vaccination. Consequently, specific antibody titers should be measured after vaccination to ensure immune protection. Immune response is improved by highly active antiretroviral therapy. Some live attenuated vaccines are considered as beneficial in some specific indications and if administered in the early stages of AIDS. However, viral load variations following administration of live attenuated vaccines have not been studied yet.

Immunizations for the immunocompromised child

Although immunocompromised children are unlikely to have optimal immune responses to vaccines, some will benefit from immunization. They should receive inactivated vaccines that are routinely recommended for immunocompetent children plus pneumococcal and influenza immunizations. Live viral and bacterial vaccines are contraindicated with the exception of MMR. It may be given to children infected with HIV who do not have severe immunosuppression. The timing of immunizations is generally the same for immunocompromised and normal children. However, the MMR schedule in children infected with HIV is accelerated, with 2 doses given 1 month apart. Susceptible children whose immunosuppression is related to a temporary condition should be vaccinated after immune dysfunction has resolved. The question of revacination for children infected with HIV who are receiving effective antiretroviral therapy is under investigation, but no specific recommendations are currently available.

[Recommended vaccines and immunoglobulins for immunocompromised patients]

A revision of the literature was made as to the recommendations given for the use of vaccines and immune globulins in persons who presented total or partial immunodeficiency, mainly related to the nineties. The analysis of 75 references led to the following principal conclusions: the vaccines containing living agents are generally inappropriate for persons who present conditions which determine serious immunodeficiency; the vaccines which contain dead agents or only antigenic fractions, despite their being less immunogenic and conferring lower rates of protection to severely immunocompromised persons as compared to normal persons, are safe and should be administered to them. Immunocompromised patients should receive immune globulins for the same indications and in the same doses as immunocompetent persons, with the exception of immune globulin to prevent measles, as recommended in a dosage of 0.5 mL/Kg for immunodeficients (15 mL, maximum).

T cell activation and human immunodeficiency virus replication after influenza immunization of infected children

BACKGROUND

T cell activation plays a major role in the ability of HIV to remain latent or to establish a productive infection. It has been hypothesized that vaccination-mediated immune stimulation can activate T cells and enhance HIV replication. Our study was designed to determine whether influenza immunization would induce T cell activation and increase HIV burdens in HIV-infected children.

METHODS

Blood samples from 16 HIV-infected children ages 6 months to 14 years were obtained immediately before and 2 and 6 to 8 weeks after the administration of influenza vaccine. The percentage of activated (CD25+) T cells was determined by flow cytometry, and HIV viral load was measured by quantitative cultures of peripheral blood mononuclear cells and plasma HIV RNA.

RESULTS

The administration of influenza vaccine was associated with significant increases in HIV viral load in 5 of 16 children evaluated. These increases in HIV burden were transient, and in four of five patients the plasma HIV RNA copy number returned to baseline 6 to 8 weeks after immunization. There was no correlation between the patient's immunologic or clinical category according to the CDC classification and either the initial viral load or the likelihood of having a significant increase after immunization. Four of the five patients who experienced increases in viral load after influenza immunization were not receiving antiretroviral therapy.

CONCLUSIONS

Our results emphasize the need for additional studies that examine the effect of routine immunizations on T cell activation and HIV replication in HIV-infected children.

Immunity to Haemophilus influenzae type b polysaccharide capsule after vaccination with the complete series of oligosaccharide CRM197 conjugate vaccine in infants with human immunodeficiency virus infection

We evaluated immunity to Haemophilus influenzae type b (Hib) in 18 human immunodeficiency virus-infected infants who were vaccinated with a complete series of Hib conjugate vaccine. Four months after the primary series, the geometric mean anticapsular antibody concentration in 11 children was 0.40 microgram/ml. There were no significant differences in CD4+ cell counts or in the Centers for Disease Control and Prevention disease classification according to the presence of immunity to Hib. Four months after the booster dose, the geometric mean anticapsular antibody concentration in the 18 children was 0.82 microgram/ml. Children with immunity were more likely than children lacking immunity to have higher CD4+ cell counts and mild human immunodeficiency virus-related disease. The majority of the anticapsular antibody concentrations were lower than in healthy children.

Comparison of the safety and immunogenicity of a pneumococcal conjugate with a licensed polysaccharide vaccine in human immunodeficiency virus and non-human immunodeficiency virus-infected children

OBJECTIVE

To compare the safety and immunogenicity of a 5-valent pneumococcal conjugate vaccine to a licensed 23-valent polysaccharide pneumococcal vaccine in HIV-infected and non-HIV-infected children > or = 2 years old.

METHODS

Thirty HIV-infected and 30 non-HIV-infected children > or = 2 years old were randomized to receive either a 5-valent pneumococcal conjugate vaccine (PCV) or a 23-valent pneumococcal polysaccharide vaccine (PPV) intramuscularly. Children who received PCV initially were given PPV after 6 weeks. Sera were obtained before and at 6 and 12 weeks after the first vaccination to determine IgG pneumococcal antibody titers by enzyme-linked immunosorbent assay to the 5 serotypes represented in the PCV.

RESULTS

Both vaccines were well-tolerated with no significant differences in the rates of fever (0 to 14%) or local reactions (0 to 40%) noted between PCV and PPV recipients. Pre-first vaccination geometric mean antibody titers (combined PCV and PPV recipients) to 3 of the 5 pneumococcal types tested were significantly lower in HIV-infected than in non-HIV-infected children (in microgram/ml: type 6B, 0.179 vs. 0.565; type 14, 0.026 vs. 0.060; type 23F, 0.025 vs. 0.119, respectively; P < 0.05). Fewer > or = 4-fold titer rises were observed in HIV vs. non-HIV-infected children whether they received PCV initially (60% vs. 79%, P < 0.05) or PPV (31% vs. 59%, P < 0.05). Also PCV elicited more > or = 4-fold titer rises compared with PPV in HIV-infected (60% vs. 31%, P < 0.05) and non-HIV-infected (79% vs. 59%, P < 0.05) children. No consistent antibody-boosting effect was noted in subjects who received PPV after PCV.

CONCLUSIONS

We conclude that antibody responses to natural infection, PCV and particularly PPV are poorer in HIV-infected than in non-HIV-infected children. PCV is as safe as and more immunogenic than the currently licensed PPV among HIV-infected and non-HIV-infected children.