1 Approaches to Demonstrate Effectiveness of Vaccines for Prevention of Group B Meningococcal...

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Approaches to Demonstrate Effectiveness of Vaccines for

Prevention of Group B Meningococcal Disease

Introduction

Vaccines and Related Biological Products Advisory Committee

April 7, 2011

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Purpose

• Consider a pathway for demonstration of effectiveness of sub-capsular meningococcal vaccines intended for the prevention of invasive group B meningococcal disease

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Meningococcal Vaccines

• Surface structures - Capsule- Major OMPs

PorA, PorB, RMP, Opa- Minor OMPs

many are lipoproteins- LOS – endotoxin

• Vaccines- Polysaccharide

A, C, ACYW-135 B PS poorly immunogenic

- PS-conjugates ACYW-135 B PS poorly immunogenic

- Detoxified outer membrane vesicles (OMV)

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N. meningitidis Genetic Diversity

• Mechanisms- Naturally transformable

- Extensive mechanisms for DNA uptake and incorporation

• Impact on Disease Epidemiology- Capsule type, MLST type, OMP types

- Epidemics and outbreaks - clonal

- Endemic group B disease - diverse

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Vaccine Effectiveness

• Measured in what way?- Disease incidence in US is low

- Inference from a serologic marker is a possible alternative

• Against what?- Endemic US group B disease

- Antigen sequence and expression diversity among disease strains

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hSBA as a Measure of Vaccine Effectiveness

• Evidence supports the use of bactericidal antibody, measured in hSBA assays, as a relevant serologic marker of protection- Studies of military recruits- Efficacy studies of OMP and OMV vaccines

Chile, Cuba, Norway, - Effectiveness

Brazil, New Zealand

However, • hSBA correlation to effectiveness has been strain

specific especially in pediatric populations

• Clinically relevant indication is for prevention of invasive disease caused by group B N. meningitidis - Broadly protective, not strain specific

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Demonstration of Effectiveness

• Therefore, CBER has advised that demonstration of effectiveness will depend on both the immune response to vaccine antigens AND the proportion of disease isolates that are susceptible.

- hSBA as a relevant measure of immunogenicity Bactericidal antibodies to outer membrane protein antigens

- Inference of effectiveness for prevention of group B meningococcal disease from immunogenicity Added complexity due the diversity of strains causing endemic

disease

- Additional evaluation of effectiveness post marketing Future product specific discussions

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Demonstration of Effectiveness (cont.)

• If hSBA testing of a large representative panel of disease strains is not feasible, then

• CBER will consider bridging from immunogenicity in clinical studies using strain specific hSBA to diverse disease isolates using microbiologic markers as an alternative

- Requires evidence that the marker is: Predictive of strain susceptibility to antibody

mediated killing Sensitive to the impact of both antigen variant and

expression diversity

Vaccine Effectiveness?

Clinical EndpointEfficacy

Immunogenicity Microbiologic Characterization

Vaccine Effectiveness?

Clinical EndpointEfficacy

Immunogenicity Microbiologic Characterization

X X X X X X X X X X X

Susceptibility to antibodyrelated to antigen variant

and expression level

Bridge Immunogenicityto effectiveness

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Presentations• Epidemiology of Group B Invasive Meningococcal

Disease in the US and Worldwide- Thomas Clark, MD, MPH

• Molecular Epidemiology and Antigen Diversity of Candidate Vaccine Targets- Leonard Mayer, Ph.D.

• Effectiveness of Sub-capsular Meningococcal Vaccines- Margaret Bash, MD, MPH

• Novartis Approaches- Rino Rappuoli, Ph.D.- John Donnelly, Ph.D.

• Pfizer Approaches- Kathrin Jansen, Ph.D.

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VRBPAC Discussion

• Please discuss the evaluation of effectiveness of vaccines for prevention of group B meningococcal disease based on:

- Bactericidal antibodies to OMP antigens tested in hSBA assays

- Bridging test strain specific hSBA to endemic disease isolates using microbiologic characterization that predicts strain susceptibility