Safety and Immunogenicity of Three Doses of a Five-Valent Pneumococcal Conjugate Vaccine in Children Younger Than Two Years With and Without Human Immunodeficiency Virus Infection
Objective. To assess the safety and immunogenicity of three doses of a five-valent (types 6B, 23F, 14, 18C, and 19F) pneumococcal conjugate vaccine (PCV) among children younger than 2 years who are and are not infected with human immunodeficiency virus (HIV).
Methods. A convenience sample of 18 HIV-infected children 2 years and younger (mean, 12.9 months) received three doses (each separated by 2 months) of PCV. An additional convenience sample of 33 non–HIV-infected children of virtually identical age, race, and sex as the HIV-infected group were randomized in a double-blind fashion to receive three doses of PCV or saline placebo. Safety data were collected for 72 hours after each vaccination. Sera were obtained before each and 1 month after the third vaccination to determine vaccine type-specific immunoglobulin G pneumococcal antibody titers by an enzyme-linked immunosorbent assay.
Results. Seventeen HIV- and 30 non–HIV-infected children completed the study. The PCV was well tolerated by both HIV- and non–HIV-infected children. No significant differences in local or systemic reactions were noted between HIV- and non–HIV-infected PCV or placebo recipients. Three doses of PCV were immunogenic, as evidenced by 16- to 659-fold increases in type-specific geometric mean antibody titers over prevaccination levels in HIV- and non–HIV-infected children. With respect to an arbitrary protective level, 78% of the antibody titers from HIV-infected children and 88% of the titers from non–HIV-infected children were 1.0 μg/mL or greater 1 month after the third PCV dose. HIV-infected children with milder disease (Centers for Disease Control and Prevention classes N1–2, A1–2, and B1) were more likely to have protective antibody titers after the first and second PCV doses than HIV-infected children with more advanced disease (Centers for Disease Control and Prevention classes N3, A3, B2–3, and C1–3). However, after the third PCV dose, these differences disappeared.
Conclusion. Three doses of PCV seem safe and immunogenic in both HIV- and non–HIV-infected children younger than 2 years. This type of vaccine should result in a marked reduction in systemic pneumococcal disease in both HIV- and non–HIV-infected children. Given the high incidence of invasive pneumococcal disease in HIV-infected children, this vaccine may markedly improve the quality of life for this unfortunate group of children.
Infants and young children with human immunodeficiency virus (HIV) type 1 infection have a markedly higher incidence of systemic infections caused by Streptococcus pneumoniae compared with their non–HIV-infected counterparts.1-3 In fact, two recent birth cohort studies revealed an incidence of more than 10 cases of systemic pneumococcal infections per 100 patient-years of observation in HIV-infected children younger than 5 years.1,2 Therefore, prevention of systemic pneumococcal disease in HIV-infected children should improve the quality of life of these children. Currently, a 23-valent pneumococcal polysaccharide vaccine is available and is recommended for HIV-infected children older than 2 years.4 Unfortunately, this polysaccharide vaccine is poorly immunogenic in all infants and also in HIV-infected children older than 2 years.5-7
New candidate vaccines are being developed in which pneumococcal cell wall saccharides are joined to protein carriers.8 A multivalent candidate vaccine in which pneumococcal saccharides are coupled to cross-reacting materials (CRM)197 diphtheria protein has been demonstrated to be safe and immunogenic in non–HIV-infected infants.9 This vaccine has also been demonstrated to be as safe as and more immunogenic than the standard pneumococcal polysaccharide vaccine in HIV- and non–HIV-infected children older than 2 years.6
The purpose of this study was to compare the safety and immunogenicity of a five-valent pneumococcal conjugate vaccine (PCV) administered to HIV- and non–HIV-infected children younger than 2 years with placebo administered to non–HIV-infected children younger than 2 years.
A convenience sample of 18 HIV-infected children younger than 2 years was enrolled from the Pediatric AIDS Care and Evaluation Clinic at the University of Maryland Medical Center. This clinic provides longitudinal and acute care for approximately 130 children with documented HIV infection. Also, a convenience sample of non–HIV-infected children was recruited from the medical center's Pediatric Ambulatory Center, a clinic that provides longitudinal and acute care for more than 7000 children in inner-city Baltimore. Two non–HIV-infected children, matched for age (±3 months), race, and sex, were recruited simultaneously for each HIV-infected child. All children were enrolled after informed written consent was obtained from a parent or legal guardian. The study protocol was approved by the Institutional Review Board at the University of Maryland at Baltimore.
Inclusion criteria for the HIV-infected group included age between 2 and 24 months, a positive HIV (type 1) serologic test result (enzyme-linked immunosorbent assay [ELISA] and Western blot) at 15 months or older, and two positive HIV early diagnostic test results, including coculture and/or HIV DNA identification by polymerase chain reaction (not done on cord blood). The control group consisted of healthy children born to parents without HIV risk factors; however, HIV serologic analyses were not performed on these children.
Exclusion criteria included the receipt of blood products within 3 months before enrollment, known primary immunodeficiency, history of receiving pneumococcal vaccine, and history of invasive pneumococcal disease (positive isolate from a normally sterile site other than the middle ear) within 3 months of enrollment. No other inactivated vaccines were to have been administered within 2 weeks of study vaccination.
Demographic information such as age, race, and gender, as well as current HIV classification according to the 1994 Centers for Disease Control and Prevention (CDC) criteria10 and CD4 lymphocyte counts for the HIV-infected group, was recorded at the first study visit.
All HIV-infected children received three 0.5-mL intramuscular injections (separated by 2 months each) into the anterolateral thigh of a five-valent, high-saccharide dose PCV consisting of 10 μg each of pneumococcal serotypes 6B, 14, 18C, 19F, and 23F oligosaccharides separately coupled to diphtheria CRM197 carrier protein by reductive amination. Other PCVs currently being tested have lower pneumococcal saccharide contents. The resultant five monocomponent conjugate vaccines were combined with aluminum phosphate as an adjuvant. For each HIV-infected child recruited, two age-, race-, and sex-matched non–HIV-infected children were simultaneously recruited and randomized in a double-blind fashion to receive either three 0.5-mL doses of PCV as described above or three 0.5-mL doses of sterile normal saline placebo. Thus, there were three experimental groups: one group of HIV-infected children received PCV; one group of non–HIV-infected children received PCV; and one group of non–HIV-infected children received the saline placebo.
Children were observed for 20 minutes after each injection to detect any immediate adverse reactions. Parents were given a diary card and asked to record their child's rectal temperature, using a digital thermometer, at 6, 24, 48, and 72 hours after each immunization. For local reactions, parents were asked to examine the injection site for erythema, induration, and tenderness each evening for 3 days. The parents were asked to quantify the size of the induration and erythema by stating whether it was greater or less than 25 mm (the size of a quarter). Tenderness was assessed by touching the vaccinated area and observing the child's reaction. Parents were asked to record whether the pain limited the function of the leg (ie, difficulty walking if age appropriate). For systemic reactions, parents were asked to record whether their child had loss of appetite, increased fussiness or sleepiness, vomiting, or rash. A study nurse contacted the parent by telephone at 24 and 72 hours after immunization to record these findings.
Blood Samples and Laboratory Studies
Four venous blood samples were obtained; one immediately before each of the three immunizations and a fourth sample 1 month after the third immunization. Sera were used to measure type-specific (6B, 14, 18C, 19F, and 23F) pneumococcal immunoglobulin G antibodies by ELISA after exposing the sera to pneumococcal ELISA absorbent, which does contain C-polysaccharide, to remove nonspecific pneumococcal antibodies.11 All serologic assays were performed, in a blinded fashion, at Wyeth-Lederle Vaccines and Pediatrics (West Henrietta, NY). The antibody concentrations were standardized to the assigned values of Food and Drug Administration reference serum 89SF. The lower limit of detection of this antibody assay was 0.01 μg/mL, and antibody concentrations lower than this value were assigned half this value, 0.005 μg/mL.
Categorical data such as the proportion of children with pneumococcal antibody levels of 1.0 μg/mL or greater or the proportion having adverse events were compared among groups using χ2 analysis or Fisher's exact test when appropriate. All serologic data were logarithmically transformed, and group means reported as the antilogarithm (geometric mean antibody titer [GMT]). Continuous variables between two groups were compared using the two-tailed Student's t test. Comparisons of continuous variables between more than two groups were performed using the Studentized range test.12 Repeated measures analysis of variance (ANOVA) was used to investigate the time-experimental group effect and the time-HIV symptom group effect. All statistical analyses were performed using SAS (Cary, NC) Windows version 6.08 analytical software. Two-tailed P < .05 was considered statistically significant.
Characteristics of Study Groups
A total of 18 HIV-infected and 33 non–HIV-infected children were enrolled in the study. The recruitment goal of 36 non–HIV-infected children was not achieved before the expiration date of the lot of PCV provided. Seventeen non–HIV-infected children received PCV, and 16 received the placebo.
Four children failed to complete the study. One HIV-infected child died of central line sepsis approximately 2 months after the first and only PCV dose. Three non–HIV-infected children were lost to follow-up after the first placebo dose; however, safety information was collected around this dose.
As per the design of the study, the PCV recipients (both HIV and non–HIV infected) and placebo recipients were similar in terms of demographic characteristics. The mean age of the children was 12.9 (range, 6 to 23) months. Ninety-four percent of the children were African-American, and 6% were white. Forty-seven percent of the children were boys. Within the HIV-infected group at the time of the first vaccination, 11 children had mild (classes N1–2, A1–2, and B1) and 7 children had advanced (classes N3, A3, B2–3, and C1–3) HIV disease using the 1994 CDC HIV classification system. The numbers of children in each specific CDC category at the time of enrollment were: N1, n = 7; N2, n = 2; A1, A3, B1, B2, B3, and C1, n = 1 each; and C3, n = 3.
Only minor adverse reactions were observed for any of the three study groups within 72 hours after each vaccination (Table1). No child had an immediate reaction after vaccination. No child had a temperature greater than 39°C or any clinically significant local reactions (redness or induration of >25 mm or limitation of movement of an extremity). Systemic reactions were highest after the first vaccine (or placebo) dose, ranging from 0% to 6% for loss of appetite, 0% to 11% for increased fussiness, 0% to 17% for increased sleepiness, 0% to 6% for vomiting, and 0% for rash. No child had high-pitched or continuous crying for more than 3 hours. There were no statistically significant differences in the rates of local and systemic adverse reactions between the two groups of children who received PCV and the group of children who received placebo (Table 1). Importantly, there was no trend toward more frequent adverse reactions after the second and third vaccinations.
Of the 975 possible serologic assays (195 blood draws × 5 serotypes for each draw), adequate sera were obtained to measure 958 results (98%). GMTs obtained immediately before each and 1 month after the third vaccination are shown in Table 2. There were no significant differences noted between prevaccination titers among the HIV-infected and all non–HIV-infected children. After the second and third vaccinations, all the GMTs were statistically significantly greater for the PCV recipients (either HIV or non–HIV infected) compared with placebo recipients. Even after the first vaccination, three of five serotypes tested from HIV-infected and all 5 serotypes tested from non–HIV-infected PCV recipients had statistically higher GMTs than non–HIV-infected placebo recipients. The type-specific pneumococcal GMT rise from before the first to after the third PCV for the HIV-infected children ranged from 42- to 659-fold and for the non–HIV-infected children ranged from 16- to 511-fold. In this small sample, there were no statistically significant differences in type-specific postvaccination GMTs between HIV- and non–HIV-infected PCV recipients. Repeated measures ANOVA demonstrated a significant time-experimental group effect for all serotypes (P < .001 for types 14, 18C, 19F, and 23F;P < .05 for type 6B).
In terms of an arbitrary protective antibody cutoff, clearly the PCV had a major impact (Table 3). Even after one dose of PCV, more than one third of the HIV-infected and almost half of the non–HIV-infected PCV recipients' antibody titers were 1.0 μg/mL or greater, compared with 2% of the titers from the placebo recipients (P < .05). The proportion of titers greater than 1.0 μg/mL increased after each PCV dose, with 78% of the titers from HIV-infected children and 88% of the titers from non–HIV-infected children being 1.0 μg/mL or greater after the final dose compared with 6% of the titers from placebo recipients (P < .05).
Factors Associated With Antibody Response in Study Groups
Using the 1994 CDC pediatric HIV classification system, HIV-infected study children were grouped into mild (N1–2, A1–2, and B1), and advanced (N3, A3, B2–3, and C1–3) disease.10Children with mild HIV disease (n = 11) had slightly higher pneumococcal GMTs to all five vaccine serotypes at all postvaccination blood draws compared with children with advanced HIV disease (n = 7). However, statistically significant differences in GMTs were only noted after the first PCV dose for serotype 19F (0.90 vs 0.11 μg/mL) and after the second PCV for serotypes 23F (1.59 vs 0.32 μg/ml) and 18C (4.31 vs 0.58 μg/mL) for children with mild HIV disease compared with those with advanced HIV disease, respectively (P < .05). After the third PCV dose there were no statistically significant differences in GMTs noted between children with mild compared with those with advanced HIV disease. Repeated measures ANOVA demonstrated no significant time-HIV symptom group effect.
In terms of protective antibody levels, 1 month after the first and second PCV doses, there was a higher proportion of titers (combined five serotypes) of 1.0 μg/mL or greater from children with mild HIV disease compared with children with advanced HIV disease (Table4). Also, 1 month after the second PCV, children with mild HIV disease were more likely to have at least four of five of the vaccine-specific titers of 1.0 μg/mL or greater compared with children with advanced HIV disease. However, these differences disappeared after the third PCV.
Pre–first vaccination CD4 counts or proportions were age adjusted into categories 1 through 3 based on 1994 CDC guidelines.10Category 1 included CD4 counts of 1500 or more cells/mm3 or CD4% of 25% or greater for children younger than 12 months and CD4 counts of 1000 or more cells/mm3 or CD4% of 25% or greater for children 1 through 5 years of age. In the present study, children with lower CD4 counts or percentages were combined into category 2–3. In this study, 10 HIV-infected children had category 1 CD4 cells, and 8 had category 2–3 cells just before the first vaccination.
In general, the antibody responses to PCV were good regardless of CD4 category (Table 4). There were no statistically significant differences in GMTs between HIV-infected children who had category 1 compared with those with category 2–3 CD4 cells. However, there was a higher proportion of pneumococcal titers of 1.0 μg/mL or greater in HIV-infected children who had category 1 CD4 levels compared with titers in children with category 2–3 CD4 cells after the second dose of PCV (Table 4). However, this difference disappeared after the third dose of PCV. There were no statistically significant differences noted between CD4 categories and the proportion of children who had at least four of the five vaccine-specific serotype titers of 1.0 μg/mL or greater.
There were no statistically significant differences in pneumococcal GMTs or proportion of titers of 1.0 μg/mL or greater noted between PCV recipients 12 months and younger compared with older children, regardless of HIV status.
To our knowledge, this is the first study that investigates the safety and immunogenicity of repeated doses of a multivalent PCV in HIV-infected infants. Importantly, these profiles were simultaneously contrasted with those of non–HIV-infected children of virtually identical age, race, and gender who received PCV or placebo.
Adverse reactions associated with PCV in both the HIV- and non–HIV-infected groups were mild and not significantly different from those associated with the placebo. These findings were expected, because multiple doses of another conjugate bacterial vaccine,Haemophilus influenzae type b CRM197, have also been shown to be safe in infants.13 Also, one dose of PCV has been safely given to HIV-infected children 2 years and older.6 There has been some concern about giving multiple doses of plain polysaccharide pneumococcal vaccine because of occasional severe local responses.14 In the present study, there was no trend toward increased reactinogenicity with repeated doses of PCV.
The GMTs achieved after the third dose of PCV were impressive in both the HIV- and non–HIV-infected children. In a previous study, one dose of a licensed 23-valent pneumococcal polysaccharide vaccine in children older than 2 years resulted in postvaccination GMTs (same five serotypes measured in the present study, in the same laboratory) ranging from 0.06 to 0.48 μg/mL for HIV-infected children and 0.46 to 2.37 μg/mL for non–HIV-infected children.6 These titers are severalfold (or even several hundredfold) lower than the GMTs achieved in the present study. These results are consistent with what has been observed for multiple doses of conjugate H inlfuenzae type b vaccine.15
In this study, the GMTs between HIV- and non–HIV-infected PCV recipients at each blood draw were similar. In a previous study, the differences in postvaccination GMTs between HIV- and non–HIV-infected recipients after three doses of conjugate H influenzae type b vaccine were more striking.16 However, in the previously mentioned study, the post–third vaccination sera were obtained a mean of 3 months after vaccination as opposed to 1 month for the present study. There is some evidence that antibody levels diminish more rapidly in HIV-infected children.17 Therefore, differences in postvaccination antibody levels between HIV- and non–HIV-infected children may become more pronounced with increasing time from vaccination. Future studies are needed to compare pneumococcal antibody levels over time in HIV- and non–HIV-infected children vaccinated with PCV.
In this study, a high proportion (78% to 88%) of the antibody titers were greater than 1.0 μg/mL after the third PCV dose. Even after the second PCV dose, more than 50% of the titers were above this level. Unfortunately, protective ELISA antibody levels have not been definitively established for any pneumococcal serotypes. Landesman and Schiffman18 estimated that 200 to 300 ng/mL antibody nitrogen as measured by radioimmunoassay was protective in adults. This translates to approximately 2 μg/mL antibody, as measured by ELISA. However, the validity of the older assays has been questioned, because the specificity of pneumococcal antibody assays is reduced when antibodies against C-polysaccharide are not absorbed before measurement of capsular polysaccharide antibodies.19 Data from more recent animal studies have suggested that 0.1 μg/mL serum antibody was protective against a lethal intraperitoneal pneumococcal challenge.20 Also, serum concentrations of 1.0 μg/mL have been reported to be protective against pneumococcal otitis media in an animal model.21 Therefore, using 1.0 μg/mL as an arbitrary cutoff seems reasonable and conservative until newer data are obtained.
Within the HIV-infected group, those with mild HIV disease or normal CD4 counts had better serologic responses to the first and second doses of PCV than those with advanced HIV disease. Lower serologic responses by infants with advanced HIV disease have been previously observed forH Influenzae type b conjugate vaccine.16 In the present study, three doses of PCV overcame this poor response in children with advanced HIV disease.
Finally, children younger than 12 months had pneumococcal antibody responses to PCV equivalent to those in children older than 12 months regardless of HIV status. However, none of the children was younger than 6 months. It will be important to demonstrate whether this PCV is immunogenic in even younger HIV-infected infants for two reasons: first, early vaccination is preferable, because systemic pneumococcal disease clearly occurs in HIV-infected infants younger than 1 year; and second, the degree of immunosuppression from HIV infection may increase with time, so that the earlier effective vaccination is administered the better.
The primary limitation of the study was the small sample size. However, despite this limitation, this study demonstrated significant differences in immunogenicity between PCV (both HIV- and non–HIV-infected) and placebo recipients. Even within the HIV-infected group, statistically significant differences in pneumococcal antibody responses were detected between children with mild HIV infection compared with those with advanced HIV infection.
Implication of the Study
Three doses of this multivalent PCV seem safe and very immunogenic in young HIV- and non–HIV-infected children and infants. Further studies are needed to establish the immunogenicity of this vaccine in even younger HIV-infected infants. Even though the number of pneumococcal serotypes represented in this PCV is limited (five), these serotypes represent more than 70% of the types reported to cause disease in children.22 Therefore, if multivalent PCVs are efficacious in protecting infants against systemic pneumococcal disease, then immunization of all infants born to HIV-infected mothers may result in a marked improvement of the quality of life for HIV-infected children and seroreverters alike.
This study was supported by a grant from Wyeth-Lederle Vaccines and Pediatrics.
We thank Drs Dace Madore and Sally Quartaert and Carolyn Cimino for the serologic results and Robin Flinko for technical assistance.
- Received July 19, 1996.
- Accepted September 13, 1996.
Reprint requests to (J.C.K.) Department of Pediatrics, University of Maryland School of Medicine, Western Health Building, Second Floor, 700 W Lombard St, Baltimore, MD 21201.
- HIV =
- human immunodeficiency virus •
- CRM =
- cross-reacting materials •
- PCV =
- pneumococcal conjugate vaccine •
- ELISA =
- enzyme-linked immunosorbent assay •
- CDC =
- Centers for Disease Control and Prevention •
- GMT =
- geometric mean (antibody) titer •
- ANOVA =
- analysis of variance
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- Copyright © 1997 American Academy of Pediatrics