Short-term booster effect of diphtheria toxoid in initially long-term protected individuals

Pneumococcal responses are similar in Papua New Guinean children aged 3-5 years vaccinated in infancy with pneumococcal polysaccharide vaccine with or without prior pneumococcal conjugate vaccine, or without pneumococcal vaccination

Trial design

In an earlier trial, Papua New Guinean (PNG) children at high risk of pneumococcal disease were randomized to receive 0 or 3 doses of 7-valent pneumococcal conjugate vaccine (PCV7), followed by a single dose of 23-valent pneumococcal polysaccharide vaccine (PPV23) at 9 months of age. We here studied in a non-randomized follow-up trial the persistence of pneumococcal immunity in these children at 3–5 years of age (n = 132), and in 121 community controls of a similar age with no prior pneumococcal vaccination.

Methods

Circulating IgG antibody titers to all PCV7 and PPV23-only serotypes 2, 5 and 7F were measured before and after challenge with 1/5^th of a normal PPV23 dose. Serotype-specific memory B-cells were enumerated at 10 months and 3–5 years of age for a subgroup of study children.

Results

Serotype-specific IgG antibody titers before and after challenge were similar for children who received PCV7/PPV23, PPV23 only, or no pneumococcal vaccines. Before challenge, at least 89% and 59% of children in all groups had serotype-specific titers ≥ 0.35μg/ml and ≥ 1.0 μg/ml, respectively. Post-challenge antibody titers were higher or similar to pre-challenge titers for most children independent of pneumococcal vaccination history. The rise in antibody titers was significantly lower when pre-challenge titers were higher. Overall the relative number of serotype-specific memory B-cells remained the same or increased between 10 months and 3–5 years of age, and there were no differences in serotype-specific memory B-cell numbers at 3–5 years of age between the three groups.

Conclusions

Immunity induced by PCV7 and/or PPV23 immunization in infancy does not exceed that of naturally acquired immunity in 3-5-year-old children living in a highly endemic area. Also, there was no evidence that PPV23 immunization in the first year of life following PCV7 priming induces longer-term hypo-responsiveness.

Trial registration

Clinicaltrials.gov NCT01414504 and NCT00219401.

Schedules for Pneumococcal Vaccination of Preterm Infants: An RCT

BACKGROUND AND OBJECTIVE

Premature infants have a higher risk of invasive pneumococcal disease and are more likely to have lower vaccine responses compared with term infants. Increasingly, immunization schedules are including a reduced, 2-dose, pneumococcal conjugate vaccine priming schedule. Our goal was to assess the immunogenicity of 3 commonly used 13-valent pneumococcal conjugate vaccine (PCV13) priming schedules in premature infants and their response to a 12-month booster dose.

METHODS

Premature infants (<35 weeks' gestation) were randomized to receive PCV13 at 2 and 4 months (reduced schedule); 2, 3, and 4 months (accelerated schedule); or 2, 4, and 6 months (extended schedule). All infants received a 12-month PCV13 booster. Serotype-specific pneumococcal immunoglobulin G (IgG) for PCV13 serotypes was measured by using enzyme-linked immunosorbent assay 1 month after the primary and booster vaccinations.

RESULTS

A total of 210 infants (median birth gestation, 29(+6) weeks; range, 23(+2)-34(+6) weeks) were included. After the primary vaccination, 75% (95% confidence interval [CI], 62-85), 88% (95% CI, 76-95), and 97% (95% CI, 87-99) of participants had protective antibody concentrations for at least one-half the PCV13 serotypes for the reduced, accelerated, and extended schedules, respectively. After the booster vaccination, participants receiving the extended schedule had significantly lower (P < .05) geometric mean concentrations compared with reduced (for 9 of 13 serotypes) and accelerated (for 4 of 13 serotypes) schedules, but nearly all participations, regardless of schedule or serotype, had seroprotective IgG concentrations.

CONCLUSIONS

A reduced priming schedule of PCV13 resulted in higher post-booster IgG concentrations but lower post-primary concentrations. The optimum vaccine schedule for preterm infants will therefore depend on when they are most at risk for invasive pneumococcal disease.

Short-term and long-term antibody response by mice after immunization against Neisseria meningitidis B or diphtheria toxoid

Serogroup B Neisseria meningitidis (MenB) is a major cause of invasive disease in early childhood worldwide. The only MenB vaccine available in Brazil was produced in Cuba and has shown unsatisfactory efficacy when used to immunize millions of children in Brazil. In the present study, we compared the specific functional antibody responses evoked by the Cuban MenB vaccine with a standard vaccine against diphtheria (DTP: diphtheria, tetanus, pertussis) after primary immunization and boosting of mice. The peak of bactericidal and opsonic antibody titers to MenB and of neutralizing antibodies to diphtheria toxoid (DT) was reached after triple immunization with the MenB vaccine or DTP vaccine, respectively. However, 4 months after immunization, protective DT antibody levels were present in all DTP-vaccinated mice but in only 20% of the mice immunized against MenB. After 6 months of primary immunization, about 70% of animals still had protective neutralizing DT antibodies, but none had significant bactericidal antibodies to MenB. The booster doses of DTP or MenB vaccines produced a significant antibody recall response, suggesting that both vaccines were able to generate and maintain memory B cells during the period studied (6 months post-triple immunization). Therefore, due to the short duration of serological memory induced by the MenB vaccine (VA-MENGOC-BC® vaccine), its use should be restricted to outbreaks of meningococcal disease.

Effect of increased CRM₁₉₇ carrier protein dose on meningococcal C bactericidal antibody response

New multivalent CRM(197)-based conjugate vaccines are available for childhood immunization. Clinical studies were reviewed to assess meningococcal group C (MenC) antibody responses following MenC-CRM(197) coadministration with CRM(197)-based pneumococcal or Haemophilus influenzae type b conjugate vaccines. Infants receiving a total CRM(197) carrier protein dose of ∼50 μg and concomitant diphtheria-tetanus-acellular pertussis (DTaP)-containing vaccine tended to have lower MenC geometric mean antibody titers and continued to have low titers after the toddler dose. Nevertheless, at least 95% of children in the reported studies achieved a MenC serum bactericidal antibody (SBA) titer of ≥ 1:8 after the last infant or toddler dose. SBA was measured using an assay with a baby rabbit or human complement source. Additional studies are needed to assess long-term antibody persistence and MenC CRM(197) conjugate vaccine immunogenicity using alternative dosing schedules.

The magnitude of the antibody and memory B cell responses during priming with a protein-polysaccharide conjugate vaccine in human infants is associated with the persistence of antibody and the intensity of booster response

Rapid waning of anti-polysaccharide bactericidal Ab and vaccine effectiveness is observed following infant immunization with the serogroup C meningococcal (MenC) glycoconjugate vaccine. This is despite the demonstrable presence of immunological memory. Persistence of functional Ab, therefore, appears to be the key determinant of MenC conjugate vaccine effectiveness. Ab persistence is thought to depend in the short term on the survival of plasma cells generated during priming and in the longer term on the production of new Ab secreting cells from memory B cells. In this study, we found a strong association between the level of MenC-specific Ab and the frequency of memory B cells measured at 5 mo of age (1 mo after 3-dose primary immunization with MenC conjugate vaccine), and the persistence of functional Ab at one year of age. These findings suggest that these two parameters are good markers of B cell responses to priming and can be used as predictors of long term humoral immunity induced by glycoconjugate vaccines received in early infancy.

Diphtheria, tetanus and pertussis antibodies in 10-year-old children before and after a booster dose of three toxoids: implications for the timing of a booster dose

In an open study, 502 10-year-old children, who had received primary vaccination against diphtheria and tetanus in infancy and had varying histories of pertussis disease and vaccination, were vaccinated with diphtheria-tetanus vaccine (DT) alone or with the addition of 20 microg or 40 microg of pertussis toxoid. Diphtheria toxin neutralising antibodies, pertussis toxin IgG and tetanus toxoid IgG antibodies were measured before and 1 month after the booster. All toxoids were highly immunogenic. In pertussis toxoid recipients, median levels of pertussis toxin IgG increased to 16.5 U/ml (DTaP20) and to 36 U/ml (DTaP40) in children with non-detectable (<1 U/ml) antibodies before vaccination and to >400 U/ml in children (both DTaP20 and DTaP40) with detectable antibodies before vaccination. A total of 60 children (12%) with non-detectable (<0.01 IU/ml) diphtheria antibodies and 36 children (7%) with non-detectable (<0.01 IU/ml) tetanus antibodies before the booster had lower median antibody concentrations post-vaccination than children with detectable antibodies before the booster (diphtheria: 5.12 vs. 20.48 IU/ml; tetanus: 4.0 vs. 10.0 IU/ml). There were no differences in diphtheria and tetanus antibodies after vaccination between children who did and did not receive pertussis toxoid.

CONCLUSION

10-year-old children with non-detectable diphtheria and tetanus antibodies before the booster had lower post-vaccination antibodies than those with detectable antibodies before the booster indicating a poor immunological memory. Addition of pertussis toxoid to diphtheria-tetanus vaccine did not affect the antibody responses to diphtheria and tetanus toxoids when the three toxoids were combined as a booster. Even though immunity to diphtheria and tetanus was only estimated by surrogate markers (serum antitoxin antibodies) the results indicate that a lower age for the booster dose of diphtheria-tetanus vaccine or diphtheria-tetanus acellular pertussis vaccine should be considered.

Attenuated immune response to tetanus toxoid in young healthy men protected against tetanus

Tetanus booster is a routine procedure of tetanus prevention in populations with high risk of injury, independent of the levels of protection. But the immune response in already protected individuals is not well studied. We describe the kinetics of booster response in individuals by measuring tetanus antitoxin levels by indirect ELISA. A 6-month follow up was performed on 60 boosted individuals tested before, 1 week, 1, 2, 3 and 6 months after the booster. High initial protection (mean titer 1.08 IU/ml) and less than 3-fold increase after 1 month were observed. After 1 month of stable antitoxin levels, the levels slowly decreased and reached a mean titer of 1.78 IU/ml after 6 months. Individuals with initial levels <1 IU/ml had booster response after the first month twice as high compared to those with initial level >or=1 IU/ml. However, in both groups, the decline from 1 to 6 months was about 2-fold. Individuals already protected against tetanus exhibited an attenuated, short-lasting booster response to tetanus toxoid. This was more pronounced in individuals with pre-booster levels >or=1 IU/ml, who did not improve immune protection after the booster.

Determination of tetanus antibodies by a double-antigen enzyme-linked immunosorbent assay in individuals of various age groups

In this study, tetanus immunity was determined in 549 randomly chosen individuals of various age groups in Ankara, Turkey. Antibody levels in sera of the individuals were measured using a double-antigen enzyme-linked immunosorbent assay. Overall, 66.5% (95%CI, 62.4-70.4) of the population studied was found to have basic protection (>or=0.01 IU/ml) against tetanus. Protective levels of tetanus antibodies declined progressively with age. The rate of protection in children and adolescents (aged<20 years) exceeded 90%, while only 16.3% (95%CI, 8.9-26.2) of those over 60 years of age were protected. Females over 60 years of age were less immune than males of the same age group (p=0.034). Although the rates of protection in children and adolescents are regarded as satisfactory, the rates among adults are low. Preventive measures against tetanus should therefore focus on scheduled booster immunization for adults as well as children.