Serotype-specific hyporesponsiveness to pneumococcal conjugate vaccine in infants carrying pneumococcus at the time of vaccination.

OBJECTIVE: To determine whether pneumococcal carriage at the time of 11-valent pneumococcal conjugate vaccine (PCV-11) administration interferes with immune response in infants. STUDY DESIGN: A total of 1111 Filipino infants recruited into an immunogenicity and carriage study, nested in an efficacy trial, received PCV-11 or saline solution placebo at 6, 10, and 14 weeks of age. Antibody concentrations to the most frequently carried vaccine serotypes 6B, 19F, and 23F were measured by enzyme immunoassay from sera obtained at 18 weeks and 9 months of age. Serotype-specific antibody concentration was compared between groups of children among PCV-11 recipients stratified according to their carriage status at 6 weeks of age. RESULTS: Antibody concentrations to 6B, 19F, and 23F were significantly lower at 18 weeks and 9 months of age among children who were carriers of the specific serotype at 6 weeks of age than among non-carriers of the serotype. The hyporesponsiveness was specific to the carried serotype. The specific antibody concentrations induced by PCV-11 among carriers did not differ significantly from those in placebo recipients, whereas the differences were highly significant among noncarriers. CONCLUSIONS: Pneumococcal carriage, prevalent in Filipino infants, interferes with serotype-specific immune response to primary series of PCV and has potential implications for immunization programs.

Longitudinal study on pneumococcal carriage during the first year of life in Bangladesh.

BACKGROUND: The strong herd immunity effect and the serotype replacement associated with the use of the pneumococcal conjugate vaccine have highlighted the importance of asymptomatic pneumococcal carriage. To describe the development of pneumoccoccal carriage in a developing country setting we carried out a longitudinal pneumococcal carriage study in Bangladesh. METHODS: Ninety-nine children, born in Savar, Bangladesh between May 2000 and April 2001, were enrolled in the study with their families. Nasopharyngeal samples were collected at prescheduled 2-4 week intervals from the index children and from their family members. The nasopharyngeal swabs were cultured for pneumococcal growth and pneumococci were identified and serotyped by standard methods. RESULTS: We collected 1459 samples (92% of those planned) from the 99 index children and 2865 samples from other family members. The data showed high point prevalences of pneumococcal carriage among newborns (40-50% from 8 weeks of age on), a rapid pneumococcal acquisition with age (50% of the children had been colonized by pneumococci at least once by the age of 8 weeks) and a wide range of different serogroups/types (SGT). SGT 6 and 19 accounted for 35% of the pneumococci isolated from children <1-year-old, followed by SGT 15, 23, and 10 for a total of 56%. The SGT distribution in children up to 9-year-old was similar to that among the <1 year olds, with SGT 6 and 19 predominating. Older children and adults differed from the younger children by not having clearly predominating SGTs. CONCLUSIONS: The features found in our study are typical of pneumococcal carriage in developing countries. We believe that results from longitudinal modeling of carriage based on these extensive data can have wide geographic application.

The value of nasopharyngeal culture in predicting the etiology of acute otitis media in children less than two years of age.

BACKGROUND: In selecting treatment of acute otitis media (AOM), knowledge of its etiology would be valuable. We revisited the possibility to use the nasopharyngeal culture of Streptococcus pneumoniae (Pnc) and Haemophilus influenzae (Hi) for predicting their presence in the middle ear fluid (MEF) during AOM. METHODS: The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of bacterial culture of the nasopharyngeal aspirate (NPA) in predicting the presence of the same pathogen in the MEF were assessed during AOM events among children followed from 2 to 24 months of age. RESULTS: The data comprised 586 AOM events. For Pnc, the sensitivity and NPV were high, 99% (95% confidence interval = 95-100%) and >99% (97-100%), respectively. The specificity and PPV were relatively low, 63% (57-68%) and 50% (43-56%). For Hi, the sensitivity and the NPV were lower (77%, 69-83% and 93%, 90-95%) than for Pnc, but the specificity and the PPV were higher (88%, 85-91% and 64%, 56-71%). The quantity of Pnc and Hi in the NPA was clearly related to their presence in the MEF. If both Pnc and Hi were found in the nasopharynx, Hi was more likely cultured from MEF. CONCLUSION: Together with clinical and epidemiologic features of AOM, the nasopharyngeal culture can be helpful in selecting specific antimicrobial therapy.

Field evaluation of the chessboard modification for serotyping of Streptococcus pneumoniae in a small laboratory in Bangladesh.

The chessboard modification of the quellung method for serotyping Streptococcus pneumoniae (Pneumococcus) was introduced in the Gonoshasthaya Vaccine Research Laboratory, a small laboratory in Bangladesh. We applied initial bench-side training and subsequent continuous surveillance and quality assurance as approaches for good laboratory practice. Results obtained a this laboratory on 1,101 consecutive isolates had satisfactory sensitivity (85.1-100%) and specificity (97.9-99.9%) for serotyping the 10 most common serogroups/types of pneumococci when compared with the results obtained in the Finnish reference laboratory for pneumococcal serotyping at the National Public Health Institute. We conclude that serotyping of pneumococci by the chessboard method can be introduced into a small laboratory by providing basic bacteriologic skills, adequate initial training, and continuous external support.

Pneumococcal acute otitis media in relation to pneumococcal nasopharyngeal carriage.

BACKGROUND: Acute otitis media (AOM) is closely associated with viral upper respiratory tract infections, but the most common microbial agent found in the middle ear fluid during AOM is Streptococcus pneumoniae (Pnc). Pnc is also a common colonizer of the nasopharynx, and its prevalence is further increased during the viral infection. The aim of this study was to investigate the interplay between viral infection, pneumococcal acquisition and carriage in the development of Pnc AOM. METHODS: Pnc carriage was assessed in a longitudinal study of 329 infants at scheduled visits at 3, 6, 9, 12, 15 and 18 months of age (N = 1715). The clinical outcome of the first episode of respiratory infection ("sick visit," N = 774) in the following 3-month period was recorded. The occurrence and timing of Pnc AOM in relation to serotype specific carriage at the start of the observation period were assessed. RESULTS: The occurrence, timing and duration of symptoms of the sick visits or the frequency of overall AOM were not associated with preceding pneumococcal carriage. Pnc AOM was in each case associated with concurrent carriage and 3.8 times (95% confidence interval, 1.4-10.0) more often with carriage acquired after the start of the observation period than with carriage already present at the scheduled visit. In all, 79% (55 of 70) of Pnc AOM events were caused by a serotype acquired after the start of the period. CONCLUSION: The majority of Pnc AOM events develop in association with newly acquired carriage of pneumococcus.

Association of clinical signs and symptoms with bacterial findings in acute otitis media.

In acute otitis media (AOM), a means of prediction of the bacterial pathogen based on symptoms and signs would be valuable in selecting appropriate antimicrobial treatment. Children in the control arm (n=831) in the Finnish Otitis Media Vaccine Trial were prospectively observed in a study clinic setting from the age of 2 to 24 months. In patients with AOM, myringotomy with aspiration was performed, and middle ear fluid samples were cultured for bacterial pathogens. Symptoms and signs of respiratory infections were thoroughly recorded. Streptococcus pneumoniae, Moraxella catarrhalis, and Haemophilus influenzae were the most common bacterial pathogens. Pneumococcal AOM was associated with more-severe AOM characterized by fever and earache. AOM due to H. influenzae was associated with eye symptoms and findings. Accurate prediction of a bacterial cause of infection based on symptoms and signs of AOM was not possible, but a specific cause was predicted in some situations, with a high probability of applicability to clinical practice.

Protective efficacy of a second pneumococcal conjugate vaccine against pneumococcal acute otitis media in infants and children: randomized, controlled trial of a 7-valent pneumococcal polysaccharide-meningococcal outer membrane protein complex conjugate vaccine in 1666 children.

To assess the efficacy of a 7-valent pneumococcal polysaccharide-meningococcal outer membrane protein complex conjugate vaccine (PncOMPC) against acute otitis media (AOM), 1666 infants were randomly assigned to receive either PncOMPC or control vaccine (hepatitis B vaccine) at 2, 4, 6, and 12 months of age. Of the 835 children assigned to receive PncOMPC, 187 received a 23-valent pneumococcal polysaccharide vaccine (PncPS) at 12 months of age instead. Whenever AOM was diagnosed, middle ear fluid was aspirated for bacterial culture. In the PncOMPC and control groups, there were 110 and 250 AOM episodes, respectively, in children between 6.5 and 24 months of age that could be attributed to vaccine serotypes, which indicates a vaccine efficacy of 56% (95% confidence interval, 44%-66%). The serotype-specific efficacy ranged from 37% for 19F to 82% for 9V. The 2 boosters seemed to provide equal protection against AOM, but PncPS induced markedly higher antibody concentrations. The efficacy of PncOMPC was comparable to that of the recently licensed pneumococcal conjugate vaccine.

Evolution of conjugate vaccines.

Conjugate vaccines--bacterial polysaccharides conjugated to proteins to improve their immunizing properties--have been a success story since their introduction less than 20 years ago. The Haemophilus influenzae type b conjugate vaccine has nearly eliminated invasive Haemophilus influenzae type b disease in large parts of the world. The key reasons for its success are its ability to induce immunologic memory and reduce asymptomatic carriage, hence the spread of infection. The first pneumococcal conjugate vaccine was licensed in 2000 and is already in wide demand in the USA. The first meningococcal conjugate vaccine was introduced in a nationwide program in the UK in 1999. Current discussion focuses on the efficacy of the conjugate vaccines for different end-points and the cost-effectiveness of their use globally.

Conjugate vaccines--a breakthrough in vaccine development.

The encapsulated bacteria Streptococcus pneumoniae (the pneumococcus), Neisseria meningitidis (the meningococcus) and Haemophilus influenzae type b (Hib) are the main causes of purulent meningitis, the peak incidence of which is seen in the first two years of life. The polysaccharide capsule of these bacteria is an essential virulence determinant, and antibodies to it are protective, suggesting that a polysaccharide vaccine could prevent these diseases. The young child is, however, unable to respond with antibody production to these polysaccharides, making such vaccines useless in infancy. Conjugation of the polysaccharide to a protein carrier has proven a way to solve the problem. Immunization of infants with such a Hib conjugate vaccine was shown in 1987 to result in the desired antibody production and protection from Hib meningitis and bacteremia. The Hib vaccine is now a part of national infant immunization programs in large parts of Europe, the Americas and Australia, and has resulted in the virtual disappearance of Hib disease from these areas. A group C meningococcal and 7-valent pneumococcal vaccine, available since 2000, are likewise proving highly effective in preventing bacteremic disease. Further advantages of the conjugate vaccines are their ability to elicit immunologic memory and to reduce asymptomatic carriage of the bacteria, resulting in marked herd immunity. This paper was delivered as a lecture in January 2003 in Bangkok on the occasion of the Prince Mahidol Award for a life's work in the field of vaccinology.

Evolution of the capsular regulatory genes in Streptococcus pneumoniae.

The major pneumococcal virulence determinant is its capsule, and pneumococcal epidemiology is based on 91 capsular serotypes, each corresponding to the structure of the capsular polysaccharide determined by the type-specific capsular genome. Here, we provide the beginnings of an approach to intertwine serotype epidemiology, capsular regulatory gene characteristics on the basis of existing sequence information, and the reanalysis of published epidemiological data. We present an approach to explain epidemiological characteristics of serotypes on the basis of genetic differences in their capsular regulatory genes. The part of the capsular genome that regulates capsular expression falls into 2 highly divergent sequence clans: the ancestral pneumococcal capsular regulatory gene sequences (present in 49 serotypes) and laterally transferred sequences (present in 32 serotypes). Our survey of epidemiological data showed a tendency of the ancestral type of the capsular regulatory genome to be associated with carriage and the laterally transferred sequences to be associated with invasive disease isolates. The regulatory gene region shows mosaic structures that have signatures of recent recombination events, reminiscent of structures known from antibiotic resistance genes.

Epidemiological evidence for serotype-independent acquired immunity to pneumococcal carriage.

BACKGROUND: Asymptomatic nasopharyngeal carriage is the main reservoir for transmission of Streptococcus pneumoniae. The rate of both carriage and pneumococcal disease decreases with age. To what extent these changes are the result of developing natural immunity is currently a subject of debate. OBJECTIVE: To study the hypothesis that previous carriage induces serotype-independent protective immunity to new colonization. METHODS: We compared the rates of pneumococcal acquisition for children with different previous carriage histories. We identified 435 episodes of carriage during the first year of life in follow-up data for 99 Bangladeshi children. Cox regression analysis was adjusted for serotype-specific exposure within the family and other confounding factors. RESULTS: Previous pneumococcal carriage was associated with serotype-independent protection from subsequent acquisition (hazard ratio, 0.60 [95% confidence interval, 0.39-0.90]), whereas recent serotype-specific exposure within the family was associated with an 8-fold increase in the rate of acquisition for that serotype. CONCLUSION: Our findings are consistent with the hypothesis that serotype-independent protective immunity is stimulated in young children by previous pneumococcal carriage and reduces the rate of new colonization. This immunity has the potential to modulate the development of carriage, irrespective of the colonizing serotype, and to do so starting early in infancy.

Passive protection in the infant rat protection assay by sera taken before and after vaccination of teenagers with serogroup B meningococcal outer membrane vesicle vaccines.

From a previous published clinical trial among teenagers in Iceland [Perkins BA, Jonsdottir K, Briem H, Griffiths E, Plikaytis BD, Høiby EA, et al. J Infect Dis 1998;177:683--91], we evaluated a 25% stratified subset of sera, collected before vaccination and 6 weeks after the second vaccination with either the Norwegian (n=37) or the Cuban (n=35) serogroup B meningococcal outer membrane vesicle (OMV) vaccine or the control serogroup A/C capsular polysaccharide vaccine (n=20), for protective activity in an infant rat protection assay (IRPA). Protection was assessed with both the Norwegian (44/76-SL, B:15:P1.7,16:L3,7) and the Cuban (Cu 385, B:4:P1.19,15:L3,7) vaccine strain, and the results compared with serum bactericidal assay (SBA) titres and anti-OMV IgG antibody concentrations. An IRPA response was defined as a >or=10-fold rise in protective activity compared to pre-vaccination level. Forty-six percent (42/92) of the pre-vaccination sera showed protection with strain 44/76-SL compared to only 12% (11/92) with strain Cu 385. After the second dose, 22% (8/37) of those given the Norwegian vaccine showed IRPA responses with the homologous strain compared to 65% (24/37) in SBA. The corresponding numbers with the homologous strain for the Cuban vaccinees were 14% (5/35) and 29% (10/35), respectively. Among the controls, 15% (3/20) showed IRPA responses to 44/76-SL but none to Cu 385. Correlation between IRPA activity and SBA titres or anti-OMV IgG was low, especially for pre-vaccination sera against strain 44/76-SL. We conclude that the sensitivity of IRPA described herein may not be sufficient to evaluate serogroup B OMV vaccine responses from clinical samples.

Invasiveness of serotypes and clones of Streptococcus pneumoniae among children in Finland.

Streptococcus pneumoniae (the pneumococcus) causes diseases from otitis media to life-threatening invasive infection. The species is extremely antigenically and clonally diverse. We wished to determine odds ratios (ORs) for serotypes and clones of S. pneumoniae that cause invasive disease in Finland. A total of 224 isolates of S. pneumoniae from cases of invasive disease in children <2 years of age in Finland between 1995 and 1999 were serotyped, and sequence types (STs) were determined by multilocus sequence typing. These STs were compared with a previously published carriage data set. STs from invasive disease were significantly less diverse than those from carriage (invasive disease, 0.038 +/- 0.01; carriage, 0.019 +/- 0.005). The ORs of serotypes 14, 18C, 19A, and 6B were significantly greater than 1, indicating association with invasive disease. The ORs of 6A and 11A were significantly less than 1. The difference between 6A and 6B is significant, which suggests that relatively subtle changes in the capsule may have a dramatic effect upon disease potential. We found that ST 156, the Spain(9V)-3 clone which mainly expressed serotype 14 in Finland, is strongly associated with invasive disease (OR, 10.1; 95% confidence interval, 1.3 to 79.5). Significant associations with invasive disease were also detected for STs 482, 191, 124, and 138, and associations with carriage were detected for STs 485 and 62. These results demonstrate the invasive phenotype of the serotype 14 variant of the Spain(9V)-3 clone and differences between members of the same serogroup in invasive disease potential.

Anti-PsaA and the risk of pneumococcal AOM and carriage.

Pneumococcal surface adhesin A (PsaA) is one of the common protein antigens of Streptococcus pneumoniae investigated as a possible vaccine candidate on the basis of studies in experimental animal models. The relation between the serum anti-PsaA concentration collected at 6, 12 and 18 months of age and the risk of pneumococcal carriage and acute otitis media (AOM) in the following 6 months was evaluated in 329 children of the Finnish Otitis Media (FinOM) Cohort Study. A higher anti-PsaA concentration at all three time points studied was found to predict a higher risk of pneumococcal carriage 6 months later. A higher anti-PsaA concentration at 6 months also predicted a higher risk of pneumococcal AOM during the following 6 months (RR 1.51, 95% CI 1.24-1.83), whereas a higher anti-PsaA concentration at 12 or 18 months seemed to decrease the risk of pneumococcal AOM (RR 0.94 [95% CI 0.80-1.09] and RR 0.88 [95% CI 0.73-1.07], respectively). These relations remained the same when concomitant risk factors for pneumococcal AOM were included in the models. Previous pneumococcal AOM was the most important risk factor for a subsequent pneumococcal AOM (RR 5.93 [95% CI 2.87-12.3], RR 2.2 [95% CI 1.21-4.00], and RR 3.3 [95% CI 1.72-6.32] during the three periods).

Vaccinovigilance in Europe--need for timeliness, standardization and resources.

OBJECTIVE: To identify gaps in the systems for reporting adverse events following immunization (AEFI) in Europe by means of an interactive database constructed using a standardized approach. METHODS: A comparative survey was conducted in 1999-2000, using structured questionnaires addressed to the government authorities responsible for national immunization programmes and drug safety surveillance in all European Union (EU) Member States and in Norway and Switzerland. FINDINGS: The reporting of adverse vaccine reactions (AVRs) is covered by regulations in 13 of the 17 countries. Four countries have a specialized expert group with responsibility for vaccine safety. Only six professionals work full-time on vaccine safety in the 17 countries; in four of these countries the person is medically qualified. Fourteen countries have centralized reporting systems; in 14 countries the responsible authority is the drug regulatory agency. AEFI are reported using the procedure used for adverse drug reactions (ADRs) in all except four countries. The reporting form is not usually designed for vaccines and important details may therefore not be requested. Clinical definitions for vaccine reactions are not available. Twelve countries have appropriate official definitions for events or reactions, but the list of reportable events varies considerably between countries. The assessment of adverse vaccine reactions (AVRs) is hampered by lack of exact denominator data. Feedback to the rapporteurs was provided in 13 countries, but its quality was highly variable. CONCLUSION: The database facilitated a simple comparison of vaccinovigilance systems across participating countries. Most of the problems identified related to the reporting and analysis of AEFI could be solved through standardization and intensified international collaboration. On a national level, functional vaccinovigilance systems should be the shared responsibility of the drug regulatory authority and the national immunization programme. The resources for development and management of vaccine safety systems should be urgently improved.

Concentration of antipneumococcal antibodies as a serological correlate of protection: an application to acute otitis media.

BACKGROUND: For the licensing of new pneumococcal vaccines, it is vital to be able to predict their protective efficacy on the basis of immunogenicity. However, the serological correlates of protection have not been established for pneumococcal diseases. METHODS: A total of 1666 children were immunized with the pneumococcal conjugate vaccine. Acute otitis media (AOM) events were identified, and middle-ear fluid was cultured for pneumococci. The association between the concentration of antibodies against serotypes 6B, 19F, and 23F and the risk of AOM caused by the homologous serotypes or by the cross-reactive serotype 6A was assessed. An association model was used to predict efficacy at different geometric mean concentrations (GMCs). RESULTS: An association between antibody concentration and risk of AOM was found, but with large differences between serotypes. On the basis of the association, the predicted efficacy for 19F was negligible up to the highest GMC tested. In contrast, 6B was found to be highly efficacious (>65%) at a GMC of 0.5 microg/mL. CONCLUSIONS: The results challenge the view that a new vaccine candidate should always induce antibody concentrations that are not inferior to those produced by the licensed vaccine. Furthermore, the differences between serotypes caution against defining a common correlate of protection that is applicable to all serotypes.

Long-term persistence of immunity after immunisation with Haemophilus influenzae type b conjugate vaccine.

Although Haemophilus influenzae type b (Hib) conjugate vaccines, after licensure in 1987, are now recommended for world-wide use, the duration of protective immunity afforded by them is not known. We therefore assessed the immunogenity at 9-10 years of age in 37 children who had received the first Hib conjugate, PRP-D, in infancy (the Hib-conjugate group) and were now given a dose of Hib polysaccharide (PS) as a test vaccine. The anti-Hib PS antibodies (Hib-ab) were measured before and after this test vaccination, and the values compared to those in 37 control children who had not previously received any Hib vaccine and in 13 children who had received Hib PS vaccine in infancy (the Hib-PS group). Prior to the test vaccination, the Hib-ab concentrations in the Hib-conjugate group were 3.6-fold higher than in the control group. After the test vaccination, the Hib-conjugate group had higher total Hib-ab concentrations, higher proportion of IgG and higher avidity of Hib-ab than the control or the Hib-PS group, suggesting persisting immunological memory in a Hib-c group. A mathematical model, including memory, predicted accurately the Hib-ab concentrations, which are maintained through anamnestic responses to intervening stimuli (Hib or cross-reacting bacteria).

DNA immunization followed by a viral vector booster in a Chlamydia pneumoniae mouse model.

Vaccination against Chlamydia pneumoniae would be a beneficial strategy for either preventing or controlling infection by this human respiratory pathogen that also causes persistent infections. In the present study, we used recombinant Semliki Forest virus (rSFV) particles for delivering C. pneumoniae antigens major outer membrane protein (MOMP) or outer membrane protein 2 (Omp2) to the mice or applied the prime-boost technique, where mice were first primed with naked DNA and then boosted with the viral vector coding for the same proteins. Partial protection suggested by the reduced number of cultivable bacteria from the lungs of the challenged mice was seen in mice immunized by either method with MOMP expressing constructs. A significant protection was also achieved after DNA/rSFV immunization with Omp2. DNA priming followed by rSFV boosting induced a more prominent IFN-gamma production after challenge at the site of the infection in pulmonary and mediastinal cells.

Ability of pneumococcal serotypes and clones to cause acute otitis media: implications for the prevention of otitis media by conjugate vaccines.

The relative abilities of pneumococcal serotypes and strains (clones) to cause acute otitis media (AOM) were investigated by comparing the serotypes and genotypes of pneumococci recovered from cases of AOM (n = 149) in children <2 years of age with those from nasopharyngeal carriage (n = 288) in age-matched controls from the same region. The odds ratio (OR) for association of pooled vaccine serotypes with AOM was found to be slightly elevated over unity, although this was not significantly different from that of pooled nonvaccine or vaccine-related serotypes. Comparing individual serotypes, 19F and 23F had 2- to 2.5-fold higher ORs, although these were not markedly different from the ORs of nonvaccine serotypes. None of the major clones had an OR that was significantly greater than the average, and the differences in ORs among serotypes and clones were much less than those for invasive disease, suggesting little variation in their ability to cause AOM. We conclude that serotype replacement may reduce the long-term efficacy of these vaccines against AOM.

Does the presence of pneumococcal DNA in middle-ear fluid indicate pneumococcal etiology in acute otitis media?

Bacterial culture of middle-ear fluid (MEF), the standard for etiologic diagnosis of acute otitis media (AOM), has revealed Streptococcus pneumoniae (Pnc) to be a major pathogen responsible for one-third of AOM cases. In the present study, we compared the results of polymerase chain reaction (PCR) based on the amplification of the pneumolysin gene with the results of pneumococcal culture, for 2595 MEF samples obtained during AOM events in 831 children who were followed from 2-24 months of age in the Finnish Otitis Media Vaccine Trial. PCR results were positive for 47.1% of the MEF samples, and culture results were positive for 27.3% of the samples. PCR-positive, culture-negative samples were associated with previous Pnc AOM in a time-dependent pattern, concurrent antibiotic treatment, low volume of MEF, and concurrent nasopharyngeal carriage. PCR-positive AOM represented a clinically less severe disease, compared with culture-positive Pnc AOM. A positive PCR result seemed to indicate the presence of viable, although often nonculturable, Pnc.