Download Large Simple Trials of Vaccine Safety

EXPERIENCE WITH
BRIDGING STUDIES IN THE
CENTER FOR BIOLOGICS
EVALUATION & RESEARCH
Susan S. Ellenberg, Ph.D.
Office of Biostatistics and Epidemiology
Center for Biologics Evaluation &
Research, U.S. FDA
Kitisato University-Harvard School of Public
Health Symposium
October 28, 2003
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ACKNOWLEDGEMENTS
• A. Dale Horne, Dr. P.H., Chief,
Vaccines Evaluation Branch, Division
of Biostatistics
• Karen L. Goldenthal, M.D., Director,
Division of Vaccines and Related
Biological Applications
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BRIDGING STUDIES IN
VACCINE DEVELOPMENT
• Bridging studies are commonly performed
in vaccine research
• Outcomes usually evaluated
– Immune responses
– Safety-related events
• Bridging studies may evaluate
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Effect of manufacturing change
Effect of formulation change
Effect of dose/schedule change
(Effect of other vaccines given concomitantly)
Validity of assumption that observed effect can
be generalized to other populations
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IMMUNE RESPONSE
• Vaccines work by stimulating the
development of protective antibodies that
can protect vaccinated individuals when
they are exposed to disease-causing
bacteria and viruses
• “Immune response” refers to the rise in
the relevant antibody levels
• In many (but not all) cases, immune
response is a reliable surrogate for clinical
efficacy (protection from disease)
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DESIGN OF VACCINE
BRIDGING STUDIES
• For studying effects of changes in
manufacturing, composition or method of
administration, randomized noninferiority
studies are generally conducted
• Examples:
– Randomize participants to receive vaccine
manufactured with original process or with new
process
– Randomize participants to receive vaccine on
original schedule or on new schedule
• Analyze results to determine if immune
responses are similar in randomized groups
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RATIONALE FOR
RANDOMIZED BRIDGING
STUDIES
• Changes made in manufacturing, or
administration, could possibly affect
vaccine efficacy or safety
• Consistency of immune responses expected
to predict consistency of prevention of
clinical disease
• Occasionally, bridging studies identify
problems with new approach
– Combining acellular pertussis vaccine with Hib
vaccine had adverse effect on Hib immune
responses for some products
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SAFETY EVALUATION
• Safety is always assessed in bridging
studies, but usually without formal
“bridging” criteria
• Changes in manufacturing are of particular
concern
– Worst case: Cutter incident, 1950’s
– Cutter was one of several manufacturers of
Salk polio vaccine, using killed virus
– Changes in manufacturing process for Salk polio
vaccine resulted in inadequate killing process;
Cutter vaccine caused hundreds of polio cases
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BRIDGING ACROSS
POPULATIONS
• These bridging studies differ from those
to assess changes in manufacturing,
formulation or delivery
• Not possible to randomize country/ethnic
group!
• Generally done as non-randomized but
controlled studies, comparing immune
responses in the region where clinical
efficacy was demonstrated, to these
outcomes in a different region
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RATIONALE FOR BRIDGING
ACROSS POPULATIONS
• Inefficient to do multiple large
clinical efficacy trials of new vaccines
• Often clinical efficacy trials are
possible only in certain regions
– Disease endemic in limited areas
– Existing vaccines in some areas
• High likelihood that vaccine effective
in one population will also be effective
in other populations
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EVIDENCE FOR “ETHNIC
FACTORS” IN VACCINE
EFFECTS
• Haemophilus influenzae b (PRP-D)
– Vaccine shown to be highly effective in
Finland
– Poor efficacy shown in Alaskans
– Possible explanations:
• Risk of Hib disease higher in Alaska
• Occurs at earlier ages
• Stronger and more rapid immune response
required for protection in Alaska
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APPROACH TO BRIDGING
STUDIES FOR VACCINE
LICENSURE IN THE U.S.
• Often not feasible to evaluate clinical
efficacy in the U.S.
• Licensed vaccines still needed for
travelers, military, certain
occupational categories
• Usual approach: perform clinical
efficacy study where disease rate is
relatively high, then “bridge” to U.S.
population with single-arm study of
new vaccine
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DESIGN OF POPULATION
BRIDGING STUDIES
• Comparison of immune responses is
fundamental objective
• Primary outcomes:
– Per cent “responders” (immune response
above threshold predicting clinical
protection from disease)
– Ratio of geometric mean concentration
of antibodies
• Study designed to have good power to
rule out important difference in
parameters of immune response
• Safety outcomes also measured
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OTHER
CONSIDERATIONS
• Since study must be observational,
try to make study in U.S. as similar as
possible to that in country where
primary study was performed
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Manufacturing considerations
Age of participants
Concomitant vaccines administered
Schedule and route of administration
Surveillance for adverse events
Timing of blood draws for response
assessment
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VACCINES LICENSED IN
U.S. WITH NON-U.S.
EFFICACY DATA
(NOT COMPLETE LIST)
• Acellular pertussis-containing
vaccines (DTaP)
• Oral polio vaccine
• Typhoid Vi Polysaccharide
• Japanese encephalitis
• Hepatitis A
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COUNTRIES PROVIDING
PRIMARY CLINICAL EFFICACY
DATA FOR U.S. LICENSURE
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Sweden
Italy
Finland
Germany
Indonesia
Thailand
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South Africa
Nepal
England
Chile
Japan
Soviet Union
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KEY CONSIDERATION:
STRAINS OF
INFECTIOUS AGENT
• Prevalent strains may differ from country
to country
• If vaccines protecting against all strains
prevalent anywhere cannot be developed,
different vaccines may have to be
developed in different regions; in such
cases, would not try to “bridge”
• Not routinely an issue, but likely will be
important for HIV vaccines in future
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