Effect of Tdap upon antibody response to meningococcal polysaccharide when administered before, with or after the quadrivalent meningococcal TT-conjugate vaccine (coadministered with the 13-valent pneumococcal CRM197-conjugate vaccine) in adult Hajj pilgrims: A randomised controlled trial

Recent advances in lipopolysaccharide-based glycoconjugate vaccines

INTRODUCTION

The public health burden caused by pathogenic Gram-negative bacteria is increasingly prominent due to antimicrobial resistance. The surface carbohydrates are potential antigens for vaccines against Gram-negative bacteria. The enhanced immunogenicity of the O-specific polysaccharide (O-SP) moiety of LPS when coupled to a carrier protein may protect against bacterial pathogens. However, because of the toxic lipid A moiety and relatively high costs of O-SP isolation, LPS has not been a popular vaccine antigen until recently.

AREAS COVERED

In this review, we discuss the rationales for developing LPS-based glycoconjugate vaccines, principles of glycoconjugate-induced immunity, and highlight the recent developments and challenges faced by LPS-based glycoconjugate vaccines.

EXPERT OPINION

Advances in LPS harvesting, LPS chemical synthesis, and newer carrier proteins in the past decade have propelled LPS-based glycoconjugate vaccines toward further development, through to clinical evaluation. The development of LPS-based glycoconjugates offers a new horizon for vaccine prevention of Gram-negative bacterial infection.

ERRATA CORRIGE

[This corrects the article on p. E530-E541 in vol. 61, PMID: 33628957.].

Effect on meningococcal serogroup W immunogenicity when Tdap was administered prior, concurrent or subsequent to the quadrivalent (ACWY) meningococcal CRM197-conjugate vaccine in adult Hajj pilgrims: A randomised controlled trial

Immune responses to the capsular polysaccharide administered in the polysaccharide-protein conjugate vaccines can be either improved or suppressed by the pre-existence of immunity to the carrier protein. Receiving multiple vaccinations is essential for travellers such as Hajj pilgrims, and the use of conjugated vaccines is recommended. We studied the immune response to meningococcal serogroup W upon prior, concurrent and sequential administration of a quadrivalent meningococcal conjugate vaccine (MCV4) conjugated to CRM₁₉₇ (coadministered with 13 valent pneumococcal vaccine conjugate CRM₁₉₇ [PCV13]), and tetanus-diphtheria-acellular pertussis (Tdap) vaccine in Australian adults before attending the Hajj pilgrimage in 2014. Participants were randomly assigned, by computer-generated numbers, to three study arms by 1:1:1 ratio. Group A received Tdap followed by MCV4-CRM₁₉₇ (+PCV13) 3-4 weeks later. Group B received all three vaccines in a single visit. Group C received MCV4-CRM₁₉₇ (+PCV13) followed by Tdap 3-4 weeks later. Blood samples obtained prior to and 3-4 weeks after immunisation with MCV4-CRM₁₉₇ were tested for meningococcal serogroup W-specific serum bactericidal antibody responses using baby rabbit complement (rSBA). One hundred and seven participants aged between 18 and 64 (median 40) years completed the study. No significant difference in meningococcal serogroup W rSBA geometric mean titre (GMT) was observed between the study arms post vaccination with MCV-CRM₁₉₇ but Group A tended to have a slightly lower GMT (A = 404, B = 984 and C = 1235, p = 0.15). No statistical difference was noticed between the groups in proportions of subjects achieving a ≥4-fold rise in rSBA titres or achieving rSBA titre ≥8 post vaccination. In conclusion, receipt of MCV4-CRM₁₉₇ vaccine prior, concurrent or subsequent to Tdap has similar immunologic response, and hence concurrent administration is both immunogenic and practical. However, further investigation into whether carrier induced suppression is a public health issue is suggested. Clinical trial registration: ANZCTR no. ACTRN12613000536763.

Immunogenicity of Potomac horse fever vaccine when simultaneously co-administered with rabies vaccine in a multivalent vaccine or as two monovalent vaccines at separate sites

Background

Potomac horse fever (PHF) is a potentially fatal enterocolitis of horses caused by Neorickettsia risticii. The disease was originally recognised almost 40 years ago in the state of Maryland in the US. It is now known to occur in many areas of North America, as well as having been described in South America and Europe. Monocomponent PHF vaccines are available, but clinical protection with vaccination has been reported to be inconsistent.

Objectives

This study was designed to assess the immunogenicity of a commercially available Potomac Horse Fever (PHF) vaccine when administered as either a monovalent PHF vaccine simultaneously co‐administered with a separate monovalent Rabies vaccine or as a multivalent PHF/Rabies vaccine in horses.

Study design

Randomised parallel group trial.

Methods

Ninety‐one client or University owned horses participated in this open‐label randomised study, with 45 horses receiving the monovalent vaccines at separate sites and 46 receiving the multivalent vaccine at a single site. Serum PHF IFA titres were determined twice prior to vaccination and at 1, 2 and 3 months after vaccination.

Results

Both vaccination protocols exhibited poor immunogenicity, with only one‐third of all the animals demonstrating seroconversion, defined as an increase in titre of greater than 400 over baseline, at any time point after vaccination. The monovalent PHF vaccine exhibited significantly greater immunogenicity in terms of the number of horses exhibiting seroconversion, as compared to the multivalent vaccine, at one (20 vs. 11, P = 0.03) and two (18 vs. 9, p = 0.02) months post vaccination. The monovalent PHF vaccine also exhibited significantly greater immunogenicity in terms of the median (interquartile range) IFA titres, as compared to the multivalent vaccine, at one (800 [200–1600] vs. 400 [200–800], P = 0.009) and 2 months (400 [200–1600] vs. 400 [100–800], P = 0.02) post vaccination. There was no significant difference between groups at 3 months in either seroconversion rate or median IFA titers.

Main limitations

This study did not assess the actual protective effects of PHF vaccination but rather used the serologic response to vaccination as a surrogate biomarker of immunity.

Conclusions

The multivalent PHF/Rabies vaccine exhibited lower immunogenicity as compared to the monovalent PHF vaccine co‐administered with a separate Rabies vaccine.