Transcript Slide 1
The Science of Influenza
Vaccine Development:
Implications for the Public
Health Practitioner
David Cho, PhD, MPH
Program Officer, Influenza Vaccine Development
Respiratory Disease Branch, DMID, NIAID
Goals of the Presentation
Describe the basic scientific differences between
seasonal and pandemic influenza
Explain what researchers are doing to overcome the
challenges that a pandemic strain brings
Explain what practitioners should consider in
preparation for a pandemic
Characteristics of a Pandemic Influenza
Virus
Influenza A virus with a novel hemagglutinin or novel
hemagglutinin and neuraminidase in man
Susceptibility (no neutralizing antibody) to the novel
virus in a large proportion of the population
Demonstration of the virus to cause and spread
person-to-person in a sustained fashion
Influenza Virus Nomenclature
Source: Subbarao/Murphy
Clinical Burden of Influenza Virus
Morbidity and Mortality
Previous pandemics
1918 H1N1 transferred
from birds?: > 40 million
deaths worldwide
1957 H2N2 avian-
human reassortant:
> 2 million deaths
1968 H3N2 avian-
human reassortant:
> 1 million deaths
Seasonal influenza
Millions of human cases;
hundreds of thousands of
hospitalizations yearly in the
US alone
Influenza and pneumonia:
7th leading cause of mortality
in the US in 2002
20,000 to 40,000 deaths
annually US
250,000 to 500,000 deaths
annually worldwide
Clinical Burden of Influenza Virus
Morbidity and Mortality (continued)
H5N1 Avian influenza
Seasonal influenza
Millions of human cases;
290+ documented
hundreds of thousands of
human cases
hospitalizations yearly in the
170+ deaths
US alone
Influenza and pneumonia: 7th
Over 3 ½ + years, fewer
leading cause of mortality in
than 100 documented
the US in 2002
cases/ year
20,000 to 40,000 deaths
annually US
250,000 to 500,000 deaths
annually worldwide
Cumulative Number of Confirmed Human
Cases of Avian Influenza A/(H5N1) Reported to
WHO 11 April 2007
Country
cases
deaths
Azerbaijan
8
5
Cambodia
7 (1)
7 (1)
China
24 (2)
15 (1)
1
0
Egypt
34 (16)
14 (4)
Indonesia
81 (6)
63 (5)
Iraq
3
2
Lao People’s Dem Rep
2
2
Nigeria
1
1
Thailand
25
17
Turkey
12
4
Viet Nam
93
42
291
172
Djibouti
Total
> 50%
mortality
Cases and countries shown in gold for events since January
2007. WHO reports only laboratory-confirmed cases.
H5N1 outbreaks in 2005 and major flyways of migratory birds
(situation on 30 August 2005)
Mississippi
Americas
flyway
East
Atlantic
flyway
Atlantic
Americas
flyway
Black Sea/
Mediterranean
flyway
Districts with
H5N1 outbreaks
since January
2005
Pacific
Americas
flyway
East Africa
West Africa
flyway
Central
Asia
flyway
East Asia/
Australian
flyway
Sources: AI outbreaks: OIE, FAO, and Government sources. Flyways: Wetlands International
Schematic Version of Influenza Virus
(continued)
Influenza A subtypes:
16 Hemagglutnins (HA)
9 Neuramindases (NA)
All subtypes: endemic in birds
H1N1, H2N2, H3N2: endemic in
people
HA trimers: Binds sialic acid and
fuses viral and cell membranes
NA tetramers: Removes sialic acid
to prevent adherence to self or cell
during budding
Schematic Version of Influenza Virus
(continued)
RNA Polymerases (PB1, PB2,
PA) attached to each RNP
Nucleoprotein (NP) binds RNA
and Matrix protein (M1)
On viral and infected cell
surface:
M2 tetramers
Hydrogen ion channel
In infected cell:
NS1
Binding host proteins
Role in IFN resistance
Emergence of New Human Influenza
Subtypes
H5N1 Virulence Factors in Mammals
HA with multibasic amino acid motif (RERRRKKR) at
the HA1-HA2 cleavage site
Polymerase genes adapted to mammalian host
1997 H5N1 with PB2 lysine at AA position 627
2004 H5N1 with polymerases from human source
more virulent in ferrets than same H5N1 with
polymerases from avian source
NS1 gene adapted for mammalian host
Inhibition of interferons
Increased TNF alpha
Source: Salomon et al. JEM 2006;203:689.
What Makes the HA Highly Pathogenic?
Source: Horimoto and Kawaoka. Nature Reviews Microbiology, 2005
Questions?
Common Features of H5N1 in Humans
Contact with sick/dying poultry
Frequently healthy young person
Average age <18
Incubation period 2–4 days from probable exposure
Presenting symptoms fever, dyspnea, cough
Diarrhea more common than expected with
influenza
Leukopenia/lymphopenia/thrombocytopenia
Metabolic abnormalities
Common Features of H5N1 in Humans
(continued)
High frequency of progressive pneumonia
Mostly primary viral
Occasional contribution of bacteria?
• (Staphylococcus aureus and Haemophilus
influenzae)
Hepatic necrosis and acute tubular necrosis
High mortality rate in spite of
antiviral/steroid/antibacterial treatment
Common Features of H5N1 in Humans
(continued)
Diffuse activation of the innate immune system
(“cytokine storm”) with increased levels of:
Interleukin 1 beta
Interleukin 6
Interleukin 8
Tumor Necrosis Factor alpha
Interferon alpha
Interferon gamma
Interferon inducible protein 10
Soluble Interleukin 2 receptor
Monocyte chemoattractant protein 1
Chest Radiographs of Patient with Severe
H5N1 Influenza Pneumonia: Vietnam, 2004
Source: Tran et al. N Engl J Med 350:1171, 2004
Additional H5N1 Virulence Factors in
Humans
HA receptor binding
Two ketosidic linkages of sialic acid to galactose:
alpha 2,3 and alpha 2,6
Avian HA preference for alpha 2,3 linkage
Human upper airway predominantly alpha 2,6 linkage
Human lower airway more abundant in alpha 2,3
linkage
Possibly contributes to the high incidence of
primary viral pneumonia caused by H5N1
viruses
Source: Shinya et al. Nature 2006;440:435
Evidence for Person-to-Person H5N1
Transmission (Not Sustained)
Possible instances of infection of health care
workers during 1997 outbreak in Hong Kong
Family clusters Vietnam, Thailand* and
Indonesia**
Cluster in Indonesia suggests human to human
to human transmission before the chain
extinguished***
(* Ungchusak et al. N Engl J Med 2005;352:333-340
** Kandun et al. N Engl J Med 2006;355:2186-2194
***Normile Science 2006;312:1855)
Detection of H5N1 Viruses: Lessons from
Recent Experiences
Throat samples may give higher yield than nasal samples,
but both worth examining
Rapid tests poor negative predictors and lack specificity
But microarray methods improving and may provide sensitivity and
specificity
Polymerase chain reaction (PCR) increases sensitivity but
success depends on the primers used for amplification
Laboratory confirmation generally accepted
Viral culture
Positive PCR for H5N1 RNA
• (see www.cdc.gov/mmwr/preview/mmwrhtml/mm5505a3.htm)
Positive immunofluoresence using a monoclonal
antibody for H5
4-fold or greater rise in H5-specific antibody in
paired acute and convalescent sera
Questions?
Antiviral Therapies for Influenza
Antiviral Agents for Treatment of H5N1
Viruses
Early treatment recommended for suspect cases but
efficacy, optimum dose, and duration uncertain
Treatment of choice is a neuraminidase inhibitor
Oseltamivir has been most frequently used
• 5 days treatment of 75 mg twice daily for adults and
dose decreases for children dependent on body
mass is standard
• Higher doses may be considered by some
authorities but no prospective studies
Oseltamivir resistance during treatment may
not result in resistance to zanamivir
Antiviral Agents for Prophylaxis of H5N1
Viruses
Oseltamivir 75 mg once daily for 7–10 days may
be considered for significant post exposure
prophylaxis
But rationale is based on evidence from studies
with other influenza A virus subtypes
Potential recipients would be poultry
workers/cullers, health care workers,
household contacts
Antiviral Agents for Treatment of H5N1
Viruses
Zanamivir administered as inhaled powder, which may be
difficult with respiratory symptoms
Amantadine/rimantadine resistance common in Asian H5N1
viruses
Possibly from agricultural use of drugs
Amantadine/rimantadine susceptibility of some recent strains
(African/European/Middle East)
May be clade specific
May be a role for M2 inhibitors
Other drugs (ribavirin and interferon) may also be considered
but no value clearly documented
Clinical studies in progress
Peramivir (injectable neuraminidase inhibitor)
CS8958 (once daily neuraminidase inhibior)
705 (polymerase inhibitor)
Studies may start soon with FluDase (sialidase to remove viral receptors)
Pandemic Influenza Preparedness:
Complementary Roles Within DHHS
NIH Trials with sanofi pasteur H5N1
A/Vietnam/1203/2004
Adults (18 – 64y; 7.5, 15, 45, 90ug)*
Immune response observed at all dose levels after a single
dose, unadjuvanted vaccine
2 x 90mcg doses produced most frequent and highest
antibody responses
April 17, 2007 FDA approval of sanofi vaccine at 90 mcg
dose for persons exposed to H5N1
Additional studies in elderly (65y+; 45 or 90ug);
children (2–9y; 45ug)
Immunogenicity results similar to adults
(* Treanor et al. N Engl J Med 2006; 354:1343-1351)
Dose Optimization of Inactivated H5N1
Vaccines: Aluminum Adjuvants
Controlled trials completed or planned
CSL Australia: subvirion vaccine +/- AlPO4
Baxter Austria: whole virus +/- AlOH
Novartis UK: subunit vaccine +/- AlOH
Sanofi France and US: subvirion vaccine +/- AlOH in
adult and elderly populations
Summary
Vaccines well tolerated with or without aluminum
adjuvant
Immunogenicity: Aluminum adjuvants do not show a
clear advantage over vaccine alone
Dose Optimization of Inactivated H5N1
Vaccines: Other Adjuvants
Trials with other adjuvants
GSK: subvirion vaccine +/- AS (proprietary adjuvant
system)
Novartis UK: subunit vaccine with MF59 (proprietary
adjuvant system
Summary
Vaccines well tolerated with or without adjuvant
but somewhat increased local reactogenicity
Immunogenicity: Adjuvants result in more
frequent and higher antibody responses
Dose Optimization of Inactivated H5N1
Vaccines: Route
Trials with other alternate route of administration
Sanofi subvirion vaccine given intradermal (ID) at reduced
dose or intramuscular (IM) at higher dose
Summary
Vaccines well tolerated but increased local reactogenicity
with intradermal administration
Immunogenicity: High doses IM more immunogenic
than lower doses ID
Additional studies planned for better direct
comparison of same dose given ID and IM
Source: The WHO Global Influenza Program Surveillance Network
Keeping up with H5N1 Drift: Vaccine
Reference Virus Efforts Underway
Clade 1 vaccine; trials underway
Vaccine candidates: A/VN/1203/2004 and A/VN/1194/2004
Clade 2 - subclade 2 candidates available; vaccine
production ongoing
CDC: Indonesia/05 (Sanofi US; DHHS)
NIBSC: A/Turkey/Turkey/1/05
St. Jude: A/BHG/Qinghai Lake/1A/2005 and
A/WS/Mongolia/244/05
Clade 2 - subclade 3 candidates in development
CBER/FDA: A/Duck/Laos/3295/06
CDC: A/Anhui/1/2005
St. Jude: A/Japanese White Eye/HK/1038/06
Questions?
What Can We Expect of H5N1 Influenza?
Since 2003, increasing number of countries in
Africa, Asia, and Europe have documented H5N1
virus in poultry or migratory birds.
Continued H5N1 evolution, possibly amplified by
uncontrolled transmission in high-density poultry.
Human cases track exposure to infected poultry
and are accelerating in frequency.
Clusters and potential human-to-human
spread plus epidemic influenza provide
continuing chance for reassortment.
Hong Kong model for eliminating infected
poultry and preventing human illness
Agricultural surveillance and action are critical
early steps.
Enforcement of market sanitation.
Poultry segregation (quail as asymptomatic
carriers eliminated).
Vaccination with agricultural vaccine
(asymptomatic infections possible).
Difficult to implement because of social
and economic concerns.
Annual Influenza Vaccine Production
Bulk
vaccine
production
Millions of
chickens
Global
surveillance
(ongoing)
WHO
strain
selection
Manufacturers
assess growth &
yield of
candidates
Antigenic
relatedness
confirmed
Sheep sera
FDA potency
reagents
Millions of
fertilized
eggs
PHS
strain
selection
Purified
HA
Standard
antigen
~1 rooster for
10 hens
FDA approves
supplement to
license
Coordinated
collaborative
&
complex!
Filled into vials/
syringes
Formulated lots
Generation of high
yield reassortants
“candidates”
? Demand
Distribution/
vaccine use
? Severity of Season
? Recommendations
FDA release
testing
Influenza Vaccine Production Timeline
U.S. Seasonal Influenza Vaccine:
Production and Use
Beyond Eggs and Cell Culture: Research
Efforts to Develop New Technologies
Goal: Develop “agile” vaccine platforms
DNA
Plasmids – single or multiple gene combinations (HA +
NP + M2); conserved regions; single subtype or multiple
subtypes (H3 + H1 + H5)
Vector
Adenovirus, alphavirus, salmonella strains
Recombinant subunit
Expression systems, baculovirus, drosophila
Peptide vaccines
Synthesized multigenic peptides
Vector-based vaccines
Influenza Virus and Protein RNAs:
Targets for a “Universal Vaccine”
Source: Subbarao/Murphy
Seasonal
Influenza
Preparedness
Pandemic
Influenza
Preparedness