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BACKGROUND PsA-TT (MenAfriVac) is a conjugated polysaccharide vaccine developed to eliminate group A meningococcal disease in Africa. Vaccination of African study participants with 1 dose of PsA-TT led to the production of anti-A polysaccharide antibodies and increased serum bactericidal activity measured using rabbit complement (rSBA). Bactericidal responses measured with human complement (hSBA) are presented here. METHODS Sera collected before and at 28 days and 1 year after vaccination with either PsA-TT or quadrivalent polysaccharide vaccine (PsACWY) from a random, age-distributed 360-subject subset of the Meningitis Vaccine Project study of PsA-TT in Africans aged 2-29 years were tested for hSBA. Geometric mean titer, fold-rise, and threshold analyses were compared between vaccine groups and age groups. hSBA, rSBA, and immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA) results were compared and assay correlation and agreement determined. RESULTS hSBA responses to PsA-TT were substantially higher than those to PsACWY at 28 days and 1 year following immunization, similar to previously reported rSBA and IgG results. The hSBA and IgG ELISA results identified differences between age groups that were not evident by rSBA. The rSBA data indicated sustained high titers 1 year after immunization, whereas hSBA GMTs at 1 year approached 4 in young children. CONCLUSIONS The high level of protection following PsA-TT immunization campaigns is consistent with the strong hSBA immune responses observed here. Future implementation decisions will likely depend on immunologic data and their long-term correlation with disease and carriage prevention. Expanded immunologic and epidemiologic surveillance may improve the interpretation of differences between these immunoassays.

Background. Mass vaccination campaigns of the population aged 1–29 years with 1 dose of group A meningococcal (MenA) conjugate vaccine (PsA-TT, MenAfriVac) in African meningitis belt countries has resulted in the near-disappearance of MenA. The vaccine was tested in clinical trials in Africa and in India and found to be safe and highly immunogenic compared with the group A component of the licensed quadrivalent polysaccharide vaccine (PsACWY). Antibody persistence in Africa and in India was investigated. Methods. A total of 900 subjects aged 2–29 years were followed up for 4 years in Senegal, Mali, and The Gambia (study A). A total of 340 subjects aged 2–10 years were followed up for 1 year in India (study B). In study A, subjects were randomized in a 2:1 ratio, and in study B a 1:1 ratio to receive either PsA-TT or PsACWY. Immunogenicity was evaluated by measuring MenA serum bactericidal antibody (SBA) with rabbit complement and by a group A–specific immunoglobulin G (IgG) enzyme-linked immunosorbent assay. Results. In both studies, substantial SBA decay was observed at 6 months postvaccination in both vaccine groups, although more marked in the PsACWY group. At 1 year and 4 years (only for study A) postvaccination, SBA titers were relatively sustained in the PsA-TT group, whereas a slight increasing trend, more pronounced among the youngest, was observed in the participants aged

a b s t r a c t Major epidemics of serogroup A meningococcal meningitis continue to affect the African meningitis belt. The development of an affordable conjugate vaccine against the disease became a priority for World Health Organization (WHO) in the late 1990s. Licensing of meningococcal vaccines has been based on serological correlates of protection alone, but such correlates might differ in different geographical regions. If high pre-vaccination antibody concentrations/titers impacts on the response to vaccination and possibly vaccine efficacy, is not clearly understood. We set out to define the pre-vaccination Meningo- coccal group A (Men A) antibody concentrations/titers in The Gambia and study their impact on the immunogenicity of Men A containing vaccines. Data from subjects originally enrolled in studies to test the safety and immunogenicity of the MenA vaccine recently developed for Africa meningococcal A polysaccharide conjugated to tetanus toxoid, MenAfriVac ® (PsA-TT) were analyzed. Participants had been randomized to receive either the study vaccine PsA-TT or the reference quadrivalent plain polysaccharide vaccine containing meningococcal groups A, C, W, and Y, Mencevax ® ACWY, GlaxoSmithKline (PsACWY) in a 2:1 ratio. Venous blood sam- ples were collected before and 28 days after vaccination. Antibodies were assayed by enzyme-linked immunosorbent assay (ELISA) for geometric mean concentrations and serum bactericidal antibody (SBA) for functional antibody. The inter age group differences were compared using ANOVA and the pre and post-vaccination differences by t test. Over 80% of the ≥19 year olds had pre-vaccination antibody concentrations above putatively protective concentrations as compared to only 10% of 1-2 year olds. Ninety-five percent of those who received the study vaccine had ≥4-fold antibody responses if they had low pre-vaccination concentrations compared to 76% of those with high pre-vaccination concentrations. All subjects with low pre-vaccination titers attained ≥4-fold responses as compared to 76% with high titers where study vaccine was received. Our data confirm the presence of high pre-vaccination Men A antibody concentrations/titers within the African meningitis belt, with significantly higher concentrations in older individuals. Although all partic- ipants had significant increase in antibody levels following vaccination, the four-fold or greater response in antibody titers were significantly higher in individuals with lower pre-existing antibody titers, espe- cially after receiving PsA-TT. This finding may have some implications for vaccination strategies adopted in the future.

Background Group A meningococci are the source of major epidemics of meningitis in Africa. An affordable, highly immunogenic meningococcal A conjugate vaccine is needed. Methods We conducted two studies in Africa to evaluate a new MenA conjugate vaccine (PsA-TT). In study A, 601 children, 12 to 23 months of age, were randomly assigned to receive PsA-TT, a quadrivalent polysaccharide reference vaccine (PsACWY), or a control vaccine (Haemophilus influenzae type b conjugate vaccine [Hib-TT]). Ten months later, these children underwent another round of randomization within each group to receive a full dose of PsA-TT, a one-fifth dose of PsACWY, or a full dose of Hib-TT, with 589 of the original participants receiving a booster dose. In study B, 900 subjects between 2 and 29 years of age were randomly assigned to receive PsA-TT or PsACWY. Safety and reactogenicity were evaluated, and immunogenicity was assessed by measuring the activity of group A serum bactericidal antibody (SBA) with rabbit complement and performing an IgG group A-specific enzyme-linked immunosorbent assay. Results In study A, 96.0% of the subjects in the PsA-TT group and 63.7% of those in the PsACWY group had SBA titers that were at least four times as high as those at baseline; in study B, 78.2% of the subjects in the PsA-TT group and 46.2% of those in the PsACWY group had SBA titers that were at least four times as high as those at baseline. The geometric mean SBA titers in the PsA-TT groups in studies A and B were greater by factors of 16 and 3, respectively, than they were in the PsACWY groups (P

We performed a double-blind, randomized, controlled phase I study to assess safety, immunogenicity, and antibody persistence of the new meningococcal group A conjugate vaccine (PsA-TT) in healthy volunteers aged 18–35 years. Of the 74 male subjects enrolled, 24 received the PsA-TT vaccine (Group 1), 25 received the Meningoccoccal Polysaccharide Vaccine A + C™, Pasteur, Lyon, France (Group 2), and 25 received the Tetanus Toxoid Vaccine Adsorbed™, SIIL, Pune India (Group 3). No immediate reactions were observed. Local and systemic solicited reactions within 7 days post-vaccination and unsolicited adverse events (AEs) were mild and similar among the three groups and resolved without sequelae. No serious AEs were notified up to 1 year post-vaccination. Four weeks post-vaccination, a slightly higher proportion of Group 1 subjects had a four-fold increase in SBA titers compared to Group 2 subjects (83% versus 72%, p > 0.05). SBA GMTs in Groups 2 and 3 were higher than in Group 3 (p < 0.05). Serogroup A-specific IgG GMCs were significantly higher in Group 1 than in Groups 2 (p < 0.05) and 3 (p < 0.05). After 1 year SBA titers were significantly higher in Group 1 than in Group 2 (p < 0.05). The new PsA-TT vaccine was shown to be safe, immunogenic, and able to elicit persistent functional antibody titers in adults. This opens the prospective for further development and licensure of this vaccine to eliminate epidemic meningitis in sub-Saharan Africa.

The “meningitis belt” of sub-Saharan Africa runs across the continent from Senegal to Ethiopia, and this region is prone to major epidemics of meningococcal meningitis, with a high case fatality rate and serious sequelae. Until recently, most epidemics were due to group A Neisseria meningitidis (MenA). The observed reduction in meningococcal meningitis due to MenA has been due to the development of an affordable group A meningococcal vaccine, PsA-TT (MenAfriVac, Serum Institute of India, Ltd). The Meningitis Vaccine Project, a partnership between the World Health Organization (WHO) and PATH, coordinated the development, testing, licensure, and introduction of this vaccine with the aim of eliminating epidemic meningitis attributable to MenA [1–4]. Since 2010, PsA-TT has been introduced into countries across the meningitis belt through mass campaigns [5, 6]. PsA-TT is expected to confer both longer-lasting individual protection and herd protection than MenA polysaccharide vaccines. Ongoing surveillance shows that no cases of MenA meningococcal disease have occurred in vaccinated individuals [6], but the longevity of this protective immune response is not known. Prior to the introduction of PsA-TT into the African countries of the meningitis belt, multiple clinical trials assessed the safety and immunogenicity of PsA-TT. A trial conducted in children aged 12–23 months demonstrated that this vaccine was immunogenic and induced immune memory. However, antibody persistence is key in maintaining direct and indirect protection [7, 8]. We report here on the persistence of MenA-specific antibodies in individuals vaccinated with PsA-TT in early childhood.

Anti-protective antigen (PA) immunoglobulin (Ig) G, toxin neutralization, and PA-specific IgG memory B cell responses were studied in patients with bioterrorism-related cutaneous or inhalation anthrax and in a patient with laboratory-acquired cutaneous anthrax. Responses were determined for >1 year after the onset of symptoms. Eleven days after the onset of symptoms (15 days after likely exposure), anti-PA IgG was detected in 16 of 17 patients with confirmed or suspected clinical anthrax who were tested. Anti-PA IgG remained detectable 8-16 months after the onset of symptoms in all 6 survivors of inhalation anthrax and in 7 of 11 survivors of cutaneous anthrax who were tested. Anti-PA IgG levels and serum toxin neutralizing activity were strongly associated (R2=0.83). PA-specific IgG memory B cells were detectable in all 6 survivors of inhalation anthrax but in only 2 of 7 patients with cutaneous anthrax who were tested. Anti-PA IgG is an important diagnostic marker of anthrax, a predictor of serum anti-toxin activity, and a marker of immunological memory against anthrax.

In a double-blinded, randomized trial, human immunodeficiency virus (HIV)-infected adults withor = 200 CD4 cells/microl received placebo (PL), 7-valent conjugate, or 23-valent pneumococcal polysaccharide (PS) vaccine in one of the following two-dose combinations given 8 weeks apart: conjugate-conjugate, conjugate-polysaccharide, placebo-polysaccharide, placebo-placebo. A total of 67 persons completed the study. Neither significant increases in HIV viral load nor severe adverse reactions occurred in any group. After controlling for confounders, when compared with persons receiving placebo-polysaccharide, persons receiving conjugate-conjugate and conjugate-polysaccharide had higher antibody concentrations (serotypes 4, 6B, 9V and serotype 23F, respectively) and opsonophagocytic titers (functional antibody assay, serotypes 9V, 23F and serotypes 4, 6B, 9V, respectively) after the second dose (P0.05). The second dose with either conjugate or polysaccharide following the first conjugate dose, however, produced no further increase in immune responses.

This study compares the immunogenicity and safety of a single dose of a new meningococcal A conjugate vaccine (PsA-TT, MenAfriVac™, Serum Institute of India Ltd., Pune) against the meningococcal group A component of a licensed quadrivalent meningococcal polysaccharide vaccine (PsACWY, Mencevax ACWY(®), GSK, Belgium) 28 days after vaccination in Indian children. This double-blind, randomized, controlled study included 340 Indian children aged 2-10 years enrolled from August to October 2007; 169 children received a dose of PsA-TT while 171 children received a dose of PsACWY. Intention-to-treat analysis showed that 95.2% of children in PsA-TT group had a ≥4-fold response in serum bactericidal titers (rSBA) 28 days post vaccination as compared to 78.2% in the PsACWY group. A significantly higher rSBA GMT (11,209, 95%CI 9708-12,942) was noted in the PsA-TT group when compared to PsACWY group (2838, 95%CI 2368-3401). Almost all children in both vaccine groups had a ≥4-fold response in group A-specific IgG concentration but the IgG GMC was significantly greater in the PsA-TT group (89.1 μg/ml, 95%CI 75.5-105.0) when compared to the PsACWY group (15.3 μg/ml, 95%CI 12.3-19.2). Local and systemic reactions during the 4 days after immunization were similar for both vaccine groups except for tenderness (30.2% in PsA-TT group vs 12.3% in PsACWY group). None of the adverse events or serious adverse events was related to the study vaccines. We conclude that MenAfriVac™ is well tolerated and significantly more immunogenic when compared to a licensed polysaccharide vaccine, in 2-to-10-year-old Indian children.

A double-blind, randomized, controlled phase I study to assess the safety, immunogenicity, and antibody persistence of a new group A conjugate vaccine (PsA-TT) in volunteers aged 18 to 35 years was previously performed. Subjects received one dose of either the PsA-TT conjugate vaccine, meningococcal A/C polysaccharide vaccine (PsA/C), or tetanus toxoid vaccine. The conjugate vaccine was shown to be safe and immunogenic as demonstrated by a standardized group A-specific immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA) and by a serum bactericidal antibody (SBA) assay using rabbit complement (rSBA). This report details further analysis of the sera using four additional immunologic assays to investigate the relationship between the different immunoassays. The immunoassays used were an SBA assay that used human complement (hSBA), a group A-specific IgG multiplexed bead assay, and two opsonophagocytic antibody (OPA) assays which used two different methodologies. For each vaccine group, geometric mean concentrations or geometric mean titers were determined for all assays before and 4, 24, and 48 weeks after vaccination. Pearson’s correlation coefficients were used to assess the relationship between the six assays using data from all available visits. An excellent correlation was observed between the group A-specific IgG concentrations obtained by ELISA and those obtained by the multiplexed bead assay. hSBA and rSBA titers correlated moderately, although proportions of subjects with putatively protective titers and those demonstrating a >4-fold rise were similar. The two OPA methods correlated weakly and achieved only a low correlation with the other immunoassays. The correlation between hSBA and group A-specific IgG was higher for the PsA-TT group than for the PsA/C group. Within the African meningitis belt, unpredictable epidemics of meningococcal disease continue to occur every 5 to 15 years. To prevent these epidemics, a novel serogroup A conjugate meningococcal vaccine was developed. The Meningitis Vaccine Project, a partnership between the World Health Organization (WHO) and PATH (Seattle, WA) with core funding from the Bill and Melinda Gates Foundation, was created in 2001 with the goal of eliminating meningococcal epidemics in sub-Saharan Africa through the development, testing and licensure, and widespread use of serogroup A meningococcal conjugate vaccines (11) (http://www.meningvax.org). A group A meningococcal conjugate vaccine using tetanus toxoid as a carrier protein (PsA-TT) was developed at the Serum Institute of India Ltd., using a new licensed conjugation technique from the Center for Biologics Evaluation

Background. The African meningitis belt undergoes recurrent epidemics caused by Neisseria meningitidis serogroup A. During 2002, Burkina Faso documented the first large serogroup W-135 (NmW-135) meningococcal disease epidemic. To understand the emergence of NmW-135, we investigated meningococcal carriage and immunity. Methods. Immediately after Burkina Faso's epidemic, we conducted a cross-sectional survey of meningococcal carriage and seroprevalence in an epidemic and a nonepidemic district. We identified predictors of elevated NmW-135 serum bactericidal activity (SBA), a functional correlate of protection, using multivariate logistic regression. Results. The NmW-135 carriage rate was 25.2% in the epidemic district and 3.4% in the nonepidemic district (P

Nonspecific antibodies, which are thought to be nonprotective, have been shown to contribute a substantial proportion of the measured concentration in the standardized immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA) for pneumococcal polysaccharide capsular antibodies. The presence of such antibodies in human immunodeficiency virus (HIV)-infected persons has not been evaluated. The amount of nonspecific antibodies is proportional to the reduction in IgG antibody concentration that occurs with serum absorption with the heterologous polysaccharide 22F. We measured the amount of nonspecific antibodies before and after vaccination with the pneumococcal conjugate vaccine (PCV; n = 33) or the pneumococcal polysaccharide vaccine (PPV; n = 34) in HIV-infected adults with CD4 counts of ≥200 cells/mm 3 . Blood was drawn before and 2 months after vaccination. For prevaccination sera, we found a substantial amount of nonspecific antibodies for serotypes 4, 6B, 9V, and 23F (23 to 47% of measured IgG concentration), but not for serotype 14. There tended to be proportionately less nonspecific antibodies in postvaccine sera than prevaccine sera for PCV, but not for PPV. Subjects with a low HIV viral load (≤400 copies/ml) had proportionately more nonspecific antibodies than those with higher viral load before and after both vaccines. After 22F absorption, the geometric mean concentrations of antibodies were significantly higher post-PCV than post-PPV for the high viral load group for all five serotypes, but for no serotypes in the low viral load group. These findings confirm that absorption with a heterologous pneumococcal polysaccharide (e.g., 22F) is necessary to remove nonspecific antibodies in a standardized IgG ELISA for pneumococcal capsular antibodies in HIV-infected adults.

We have previously demonstrated, using functional antibody assays, that patients undergoing splenectomy for trauma exhibit a better response to pneumococcal immunization when vaccinated at 14 days postoperatively versus 1 or 7 days. However, patients immunized at 14 days failed to reach the response of normal controls. This study was conducted to determine whether even later immunization would improve the antibody response.Forty surviving patients undergoing emergent splenectomy were randomized to receive Pneumovax at 14 or 28 days after splenectomy. Blood samples were drawn at the time of vaccination (prevaccination) and 4 weeks later (postvaccination). A control group of 24 healthy adults was used for comparison. Antibody titers to four of the most common serotypes were determined by enzyme-linked immunosorbent assay and opsonophagocytic assay (OPA).Samples from 38 patient were analyzed. Each serotype and each group tested demonstrated a statistically significant increase in geometric mean enzyme-linked immunosorbent assay immunoglobulin G antibody concentration (microg/mL) and OPA titer (1/dilution) after vaccination. There were no statistically significant differences (por= 0.07) in the immunoglobulin G antibody concentrations and OPA titers between the 14-day or the 28-day study groups when compared with normal healthy adults regardless of the serotype tested. In addition, there were no differences in the antibody responses between the 14-day and the 28-day study groups.Despite our previous study suggesting that delay in vaccination after emergent splenectomy resulted in improved antibody response, antibody response was not improved any further by delaying vaccination to 28 days.

Pneumococcal conjugate vaccines will eventually be licensed after favorable results from phase III efficacy trials. After licensure of a conjugate vaccine for invasive pneumococcal disease in infants, new conjugate vaccines will likely be licensed primarily on the basis of immunogenicity data rather than clinical efficacy. Analytical methods must therefore be developed, evaluated, and validated to compare immunogenicity results accurately within and between laboratories for different vaccines. At present no analytical technique is uniformly accepted and used in vaccine evaluation studies to determine the acceptable level of agreement between a laboratory result and the assigned value for a given serum sample. This multicenter study describes the magnitude of agreement among 12 laboratories quantifying an identical series of 48 pneumococcal serum specimens from 24 individuals (quality-control sera) by a consensus immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA) developed for this study. After provisional or trial antibody concentrations were assigned to the quality-control serum samples for this study, four methods for comparison of a series of laboratory-determined values with the assigned concentrations were evaluated. The percent error between assigned values and laboratory-determined concentrations proved to be the most informative of the four methods. We present guidelines that a laboratory may follow to analyze a series of quality-control sera to determine if it can reproduce the assigned antibody concentrations within an acceptable level of tolerance. While this study focused on a pneumococcal IgG ELISA, the methods that we describe are easily generalizable to other immunological assays.

Infant vaccination with meningococcal conjugates may provide long-term protection against disease. Antibody levels and immunologic memory were assessed in 5-year-old Gambian children who received meningococcal A/C conjugate vaccination (MenA/C) in infancy. At 2 years, they were randomized to receive a booster of MenA/C (conjugate group), meningococcal A/C polysaccharide (MPS group), or inactivated polio vaccine (IPV group). All groups were revaccinated with 10 microg MPS at 5 years of age, as were 39 previously unvaccinated age-matched control subjects. Before revaccination, titers were higher in the conjugate and MPS groups than in control subjects (P.001); titers for the IPV group were similar to those for control subjects. Ten days after revaccination, the conjugate and IPV groups had similar serogroup C serum bactericidal antibody titers (3421 vs. 2790, respectively). These levels were significantly higher than those in the MPS (426) and control (485) groups (P.001). Thus, immunologic memory was sustained foror =5 years; however, MPS challenge at 2 years interfered with a subsequent memory response.

We assigned additional enzyme-linked immunosorbent assay antibody concentrations (immunoglobulin G [IgG], IgM, and IgA, and total) to the Neisseria meningitidis standard reference serum CDC1992 for groups Y and W-135 to 12 Centers for Disease Control and Prevention quality control sera. These assignments will supplement previous assignments and will aid in the evaluation of present and developing vaccines.

The bioterrorism-associated human anthrax epidemic in the fall of 2001 highlighted the need for a sensitive, reproducible, and specific laboratory test for the confirmatory diagnosis of human anthrax. The Centers for Disease Control and Prevention developed, optimized, and rapidly qualified an enzyme-linked immunosorbent assay (ELISA) for immunoglobulin G (IgG) antibodies to Bacillus anthracis protective antigen (PA) in human serum. The qualified ELISA had a minimum detection limit of 0.06 µg/mL, a reliable lower limit of detection of 0.09 µg/mL, and a lower limit of quantification in undiluted serum specimens of 3.0 µg/mL anti-PA IgG. The diagnostic sensitivity of the assay was 97.8%, and the diagnostic specificity was 97.6%. A competitive inhibition anti-PA IgG ELISA was also developed to enhance diagnostic specificity to 100%. The anti-PA ELISAs proved valuable for the confirmation of cases of cutaneous and inhalational anthrax and evaluation of patients in whom the diagnosis of anthrax was being considered. aturally occurring anthrax is a zoonotic disease of herbivores, with low-level sporadic infection of humans. Since 1950, human anthrax in the United States was confined to those occupationally at risk, with only 235 confirmed cases, mostly cutaneous, reported from 1955 to 2002 (1–3). The occurrence of human anthrax in the country and the public perception of the disease changed dramatically in the fall of 2001, with the first successful bioterrorist anthrax attack on the U.S. civilian population. This event necessitated the simultaneous development and application of qualified laboratory assays— including serologic assays—to evaluate patients suspected of having anthrax. The major obstacle to serologic analysis of human anthrax