meningococcal conjugate vaccines in children younger than 2 years of age an approach to...
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Meningococcal Conjugate Vaccines in Children Younger Than 2 Years of Age
An Approach to Demonstration of Effectiveness
Vaccines and Related Biological Products Advisory Committee Meeting
April 6, 2011
Lucia H. Lee, M.D.
Food and Drug Administration
Center for Biologics Evaluation and Research
Neisseria meningitidis
Why are meningococcal conjugate vaccines for infants and young children important?
Meningococcal Disease Incidence inU.S. Children <5 years, 1999-2008
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• Invasive meningococcal disease- Meningitis
- Sepsis• Rapid onset of illness• Morbidity
- 10-20% of individuals experience sequelae
- Limb loss, neurosensory hearing loss, cognitive deficits, seizure disorders
• Mortality- Case-fatality rates of 10-14%
Neisseria meningitidis
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• Polysaccharide encapsulated organism - Disease-causing isolates
• Serogroups - Classified based on biochemical composition of the PS capsule- Six serogroups (A, B, C, X, Y, W-135) cause invasive disease
• Polysaccharide and PS-conjugate vaccines- A,C,Y,W-135 capsular polysaccharides are immunogenic
- Anti-capsular functional antibodies are protective
Neisseria meningitidis
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• Effectiveness of a MCV for children <2 years old can be demonstrated by- Clinical efficacy studies
Low incidence of meningococcal disease and sporadic occurrence of cases in the U.S.
- Alternative approach using a serological marker of protection Bactericidal antibody
Meningococcal Conjugate Vaccines in Children <2 years oldApproach
Inferred effectiveness using serum bactericidal antibody measurement
• Mechanisms of protection
- Antibody-dependent complement-mediated bactericidal killing - Other mechanisms (e.g., opsonization)
• Individuals who have circulating meningococcal-specific functional antibodies present at the time of exposure are protected from disease
• Serum bactericidal activity with human complement (hSBA) is consistent with an in vivo biological mechanism of protection
• Bactericidal antibodies directed against the polysaccharide capsule are protective
• The presence of functional antibodies that are bactericidal, measured by hSBA assay, can be predictive of protection
Meningococcal Conjugate Vaccines in Children <2 years oldApproach
Mechanisms of Protection
Antibody-dependent complement-mediated bactericidal killing (bactericidal activity)
Antibody-dependent complement-mediated killing
Neisseria meningitidisPrinciple mechanism of protection
The complement cascade is activated by serum antibodies via the classical pathway. The final complement pathwayfor the classical and alternative pathways of complement activation is formation of a lytic membrane attack complex, which results in cell lysis.
Immunity to Meningococcal Disease
Role of Bactericidal Antibody
Immunity to Meningococcal DiseaseRole of Bactericidal Antibody
• Incidence of meningococcal disease and age-specific prevalence of bactericidal antibodies to the meningococcal-specific strain
• Studies in U.S. Army recruits • Individuals deficient in serum complement components
C5, C6, C7, or C8
Meningococcal-specific antibodies were measured by bactericidal activity in serum
Highest incidence of disease occurred at the lowest bactericidal antibody prevalence
The incidence of meningococcal disease was inversely proportional to the age-specific prevalence of bactericidal antibodies to the Mn-specific strain.
Adapted from Pollard et al. Vaccine 2001; 19: 1327-1346; and Goldschneider I, J Exp Med 1969;129:1307-1326
Naturally-acquired
bactericidal antibodies
Maternal Antibodies
Meningococcal Disease Incidence
Immunity to Meningococcal DiseaseRole of Bactericidal Antibody
• N=14,744 U.S. Army recruits• 60 cases of meningococcal serogroup C (MenC) disease
- 54 had pre-exposure blood sample + disease isolate 3 of 54 had pre-exposure hSBA titer >4
• hSBA assay- Intrinsic human complement source - Single serum dilution 1:4- Almost all individuals who developed meningococcal disease lacked bactericidal
antibodies to their pathogenic strain prior to exposure
Protection against meningococcal disease at the time of exposure is dependent on the presence of circulating meningococcal-specific bactericidal antibodies
Goldschneider I, J Exp Med 1969;129:1307-1326
Susceptibility to Disease is Strain Specific
Goldschneider et al. J. Exp. Med. 129:1307, 1969
N=492
N=438 N=54
N=24N=11
N=13
N=5
Sera + nasopharyngeal (NP) cultures
(+) bactericidal Ab
+ MenC disease
Lacked bactericidal Ab to the MenC disease isolate
Exposed to a MenC epidemic strain
Colonized, developed
bactericidal Ab
+ Acquired MenC pathogenic strain in the NP, (-) SBA to the same strain
No disease
No disease
Army Recruits- Fort Dix
Late Complement Component Deficiencies
• Persons with inherited serum complement component C5,C6,C7, or C8 deficiency are markedly susceptible to systemic meningococcal disease
Measurement of Functional Antibodies
hSBA assay
Measurement of Functional AntibodiesSBA assay
• Serological marker of protection- A measure of a biological function important in protection from
systemic disease
- Functional antibodies that are measurable in a bactericidal assay can be predictive of protection
• SBA with human complement is consistent with an in vivo biological mechanism of protection- Antibody-dependent complement-mediated bactericidal killing
- Most relevant to individual protection and assessment of vaccine immunogenicity
Serological Markers of ProtectionUse of hSBA for approval of new vaccines
• Recently licensed U.S. vaccines- MenACYW-D and MenACYW-CRM197
- hSBA has been used as a measure of immunogenicity to infer effectiveness
• Post-licensure surveillance study in the U.S.- Post-vaccination seroresponses were consistent with observed
vaccine effectiveness estimates
Meningococcal Conjugate Vaccine Experience in Infants and Young Children
Bactericidal antibodies to the PS capsule are protective
Vaccination Campaign in the United KingdomEpidemiology prior to MenC vaccine introduction
• Hyperendemic meningococcal disease- Virulent N meningititis serogroup C:2a clone
- Awareness of increased MenC disease Canada and Spain
• 1998- Incidence of MenC disease in all ages: 1.85 cases/105
- 2418 confirmed meningococcal infections
- Proportion of disease due to serogroup C 34% (26% in 1994)
• Adolescents and young adults- High case fatality rate
Estimated Total Numbers of Deaths from Meningococcal C Disease, England and Wales, 1993-1998, by Age
The total number of deaths among meningococcal serogroup C cases was highest in children <1 year of age and children 15-18 years of age.
Meningococcal Vaccines. Ed. A. Pollard, M Maiden. 2001
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Implementation phase- Routine infant immunization at 2,3,4 months old- Catch-up in children 5 months to 18 years old
1999• November
- Adolescents 15-17 years old- 3-doses: infants at 2,3,4 months old
2000• January
- 1-dose: children 12-23 months old- 2-doses: children 5-11 months old
• March-September- Children 2-4 years old- Children 5-14 years old
Vaccination Campaign in the United Kingdom
Confirmed Cases of Meningococcal C Disease Pre- and Post-Introduction of MenC Conjugate Vaccines in the U.K.
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Incidence of MenC disease in England and Wales
• Children <1 years old- 1998-1999: 16.63 cases/105
- 2001-2002: 1.02 cases/105
- 2008-2009: 0.00
• Children 1-4 years old- 1998-1999: 8.13 cases/105
- 2001-2002: 0.92 cases/105
- 2008-2009: 0.04 cases/105
Vaccination Campaign in the United KingdomPost-implemenation
Campbell et al. Clin Vaccine Immunol 2010; 17:840-847
Meningococcal C Vaccine Effectiveness in U.K. Immunized Cohorts
• Overall vaccine effectiveness (VE) 4 years after vaccination- 5 months to 18 years old: > 83%- Infant 3-dose series (2,3,4 months old): 66%- Waning immunity during the 1st year of life
• Additional dose given in the 2nd year of life - Longer protection - Sustained disease control
• Vaccine introduction and use was associated with reduced disease incidence
• Decline in circulating bactericidal antibodies was associated with decreased vaccine effectiveness and resurgence of disease
Trotter et al. Lancet 2004; 364:365-367
Summary and ConclusionsInferred effectiveness using serum bactericidal antibody measurement
• Antibody-dependent complement-mediated bactericidal killing is a principle mechanism of protective immunity to meningococcal invasive disease in both children and adults.
• Individuals who have circulating meningococcal-specific functional antibodies present at the time of exposure are protected from disease
• Post-marketing surveillance data support that meningococcal conjugate vaccine-induced bactericidal antibodies directed against the PS capsule can be effective in controlling meningococcal disease in infants and young children.
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• Serum bactericidal activity with human complement is consistent with an in vivo biological mechanism of protection
• The presence of functional antibodies that are bactericidal, measured by hSBA assay, can be predictive of protection
Inferred effectiveness using serum bactericidal antibody measurement
Summary and Conclusions (cont.)
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