Safety, reactogenicity and immunogenicity of 2-dose catch-up vaccination with 10-valent pneumococcal non-typeable Haemophilus influenzae protein D conjugate vaccine (PHiD-CV) in Malian children in the second year of life: Results from an open study

Naturally-induced serum antibody levels in children to pneumococcal polysaccharide 15B that correlate with protection from nasopharyngeal colonization but anti-serotype 15B antibody has low functional cross-reactivity with serotype 15C

BACKGROUND

Serotypes 15B and 15C have been added to new different pneumococcal-conjugate vaccines (PCV20 and V116, respectively). We determined a serum anti-15B antibody level that would be a correlate of protection (COP) against nasopharyngeal colonization and assessed functional cross-reactivity against serotype 15B and 15C in children following natural immunization.

METHOD

IgG-antibody to serotype 15B polysaccharide was measured by ELISA in 341 sera from 6 to 36 month old children collected before, at the time of, and after pneumococcal colonization caused by serotypes 15B and 15C. 155 age-matched controls who had no detected colonization caused by serotype 15B or 15C strains were used as controls. A two-step method was used for construction of COP models: a generalized estimating equation followed by logistic-regression. Opsonophagocytic (OPA) assays assessed functional cross-reactivity between serotypes 15B and 15C.

RESULTS

The derived COP for prevention of colonization was 1.18 µg/ml for serotype 15B and 0.63 µg/ml for serotype 15C, with a predictive probability of 80 %. Antibody levels did not correlate with OPA titers. 30 % of child samples, with moderate to high amounts of ELISA-measured antibody, showed no OPA titer against either serotype 15B or 15C. For remaining samples, very low or no functional cross-reactivity between serotypes 15B and 15C was measured.

CONCLUSIONS

A COP for prevention of colonization in young children based on naturally-induced antibody levels was derived for serotypes 15B and 15C that differed. Antibody levels correlated poorly with OPA titers and low functional cross-reactivity between serotypes 15B and 15C in child sera was observed.

Comparison of anti-capsular antibody quantity and functionality in children after different primary dose and booster schedules of 13 valent-pneumococcal conjugate vaccine

Different schedules for pediatric use of the 13-valent pneumococcal conjugate vaccine (PCV-13) are recommended in different countries and the U.S. Advisory Committee on Immunization Practices (ACIP) has considered potential of changing from 3 primary doses plus a booster (3p + 1) to two primary doses plus a booster (2p + 1) for protection against Streptococcus pneumoniae. In this paper, we report results of IgG antibody measured by ELISA and opsonophagocytic assay (OPA) after 2p, 3p, at child age 15 months of pre-booster and 18 months (post-booster) in serum samples opportunistically available from a prior study that focused on PCV effectiveness against AOM. A total of ~ 100 sera for each of the 4 study time points (390 sera tested) from 169 children were tested. Geometric mean concentrations (GMCs) and percentage of children exceeding the presumed protective antibody thresholds measured by ELISA and OPA were calculated. 2p doses produced lower antibody levels measured by ELISA but not OPA until the booster dose for serotypes 6A, 6B, 5 and 23F only. Booster dosing at 15 months resulted in significant increases in antibody. There was no difference in the percentage of children with ≥ correlate of protection (COP) for OPA for 2p vs 3p doses except for serotype 23F. A 2p + 0 or 3p + 0 schedule would likely result in many children failing to sustain protective levels of antibody into the second year of life. We conclude that protection from invasive pneumococcal infection in early childhood would be similar for most serotypes in PCV13 using a 2p + 1 or 3p + 1 but not a 2p + 0 or 3p + 0 schedule.

Impact of Pneumococcal Conjugate Vaccine Administration in Pediatric Older Age Groups in Low and Middle Income Countries: A Systematic Review

INTRODUCTION

Pneumococcal conjugate vaccine (PCV) is included in the World Health Organization's routine immunization schedule and is recommended by WHO for vaccination in high-risk children up to 60 months. However, many countries do not recommend vaccination in older age groups, nor have donors committed to supporting extended age group vaccination. To better inform decision-making, this systematic review examines the direct impact of extended age group vaccination in children over 12 months in low and middle income countries.

METHODS

An a priori protocol was used. Using pre-specified terms, a search was conducted using PubMed, LILACS, Cochrane Infectious Diseases Group Specialized Register, Cochrane Central Register of Controlled Trials, CAB Abstracts, clinicaltrials.gov and the International Symposium on Pneumococci and Pneumococcal Diseases abstracts. The primary outcome was disease incidence, with antibody titers and nasopharyngeal carriage included as secondary outcomes.

RESULTS

Eighteen studies reported on disease incidence, immune response, and nasopharyngeal carriage. PCV administered after 12 months of age led to significant declines in invasive pneumococcal disease. Immune response to vaccine type serotypes was significantly higher for those vaccinated at older ages than the unimmunized at the established 0.2 ug/ml and 0.35 ug/ml thresholds. Vaccination administered after one year of age significantly reduced VT carriage with odds ratios ranging from 0.213 to 0.69 over four years. A GRADE analysis indicated that the studies were of high quality.

DISCUSSION

PCV administration in children over 12 months leads to significant protection. The direct impact of PCV administration, coupled with the large cohort of children missed in first year vaccination, indicates that countries should initiate or expand PCV immunization for extended age group vaccinations. Donors should support implementation of PCV as part of delayed or interrupted immunization for older children. For countries to effectively implement extended age vaccinations, access to affordably-priced PCV is critical.