Avian influenza and pandemic threats

Transcription

1 Avian influenza and pandemic threats Philippe BUCHY MD, PhD Head of Virology Unit Director NIC Cambodia Vaccinology 2013 Bangkok, November 2013

2 Influenza viruses Influenza viruses (Orthomyxoviridae) are divided into three main types: influenza A, B, and C A viruses: infect birds, bats and other animals, as well as humans Seasonal epidemics, and all pandemics B and C viruses infect humans only and do not cause pandemics 2

3 Influenza A viruses 3

4 Influenza A viruses Hemaglutinin (HA): Precursor HA0 must be cleaved in HA1 and HA2 for the virus to be infectious Binds to sialic acid-containing receptors on the cell surface Responsible for virus penetration into cells HA is the major antigen (neutralizing Abs) and epidemics are associated with changes in this antigenic structure 4

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6 Influenza A viruses Hemaglutinin (HA): Precursor HA0 must be cleaved in HA1 and HA2 for the virus to be infectious Binds to sialic acid-containing receptors on the cell surface Responsible for virus penetration into cells HA is the major antigen (neutralizing Abs) and epidemics are associated with changes in this antigenic structure 18 different HA: 6 HA 1-16

7 Influenza A viruses Hemaglutinin (HA): Precursor HA0 must be cleaved in HA1 and HA2 for the virus to be infectious Binds to sialic acid-containing receptors on the cell surface Responsible for virus penetration into cells HA is the major antigen (neutralizing Abs) and epidemics are associated with changes in this antigenic structure 18 different HA: 7 HA 1-16 HA 17-18

8 Influenza A viruses Neuraminidase (NA): Homotetramer Head domain enzymatically active, stalk region attached to membrane Remove sialic acid from glycoproteins important antigenic determinant Inhibited by NA inhibitors (oseltamivir, zanamivir, peramivir, ) 8

9 Influenza A viruses Neuraminidase (NA): Homotetramer Head domain enzymatically active, stalk region attached to membrane Remove sialic acid from glycoproteins important antigenic determinant Inhibited by NA inhibitors (oseltamivir, zanamivir, peramivir, ) 9 NA 1-9 NA 10-11

10 Influenza pandemics 10

11 Influenza pandemics Occur when a new avian influenza strain acquires the ability infect people and to spread easily from person to person 2 ways: Reassortment: exchange of seasonal and avian influenza genes in a cell (human or pig origin) infected with both strains 11

12 Influenza pandemics 12

13 Influenza pandemics Occur when a new avian influenza strain acquires the ability infect people and to spread easily from person to person 2 ways: Reassortment: exchange of seasonal and avian influenza genes in a cell (human or pig origin) infected with both strains Mutation: an avian strain becomes more transmissible through adaptive mutation of the virus during human avian influenza infection (adaptation of the HA RBS to the human cell receptors) 13

14 Influenza pandemics 14 Herfst et al. Science, 2012.

15 Human influenza viruses bind to α2-6 receptors Epithelial cells of upper resp tract Usually mild disease Avian influenza viruses bind to α2-3 receptors Type 2 pneumocytes in lung Severe pulmonary disease 15

16 Human influenza viruses bind to α2-6 receptors Epithelial cells of upper resp tract Usually mild disease Avian influenza viruses bind to α2-3 receptors Type 2 pneumocytes in lung Severe pulmonary disease 16

17 Human influenza viruses bind to α2-6 receptors Epithelial cells of upper resp tract Usually mild disease Avian influenza viruses bind to α2-3 receptors Type 2 pneumocytes in lung Severe pulmonary disease Chan RWY et al. Virus Res

18 Pandemics of the 20 th century H1N1 H2N2 H3N2 Spanish Influenza Asian Influenza Hong Kong Influenza H1N ? Influenza A reservoir Ag drift Ag shift? 16 HA subtypes 9 NA subtypes 18

19 Pandemics of the 20 th century ~50 M. H1N1 H2N2 H3N2 Spanish Influenza Asian Influenza Hong Kong Influenza H1N ? Influenza A reservoir Ag drift Ag shift? 16 HA subtypes 9 NA subtypes 19

20 «Spanish flu» 20

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22 Pandemics of the 20 th century ~50 M. ~1-2 M. H1N1 H2N2 H3N2 Spanish Influenza Asian Influenza Hong Kong Influenza H1N ? Influenza A reservoir Ag drift Ag shift? 16 HA subtypes 9 NA subtypes 22

23 Pandemics of the 20 th century ~50 M. ~1-2 M. ~1 M. H1N1 H2N2 H3N2 Spanish Influenza Asian Influenza Hong Kong Influenza H1N ? Influenza A reservoir Ag drift Ag shift? 16 HA subtypes 9 NA subtypes 23

24 2009 pandemic Dawood et al. Lancet April 09 Aug 10: 18,500 lab-confirmed deaths reported Estimated: 201,200 deaths by respiratory disease + 83,300 deaths by cardiovascular disease (80% in patients <65 yo; 51% in Africa and SE Asia) 24

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26 Low Pathogenic/Highly Pathogenic avian influenza virus 26 LPAI HPAI

27 H5N1 virus 27

28 H5N1 virus 10 clades (0-9) 4 clades isolated from humans: 0, 1, 2 & 7 28 Guan & Smith. Virus Res

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31 H5N1 virus 31

32 H5N1 virus 32

33 15 countries >641 confirmed cases >380 deaths 33 Kaplan & Webby. Virus Res

34 H5N1 virus 34

35 H7N9 virus 35 Gao et al. NEJM 2013.

36 H7N9 virus Gao et al. NEJM lab-confirmed cases 45 deaths 36

37 H7N9 virus 37 De Groot et al. Human Vaccines & Immunotherapeutics 2013.

38 H5N1 infection control in poultry Depopulation Poultry vaccination: reduces poultry mortality (protection of naïve birds, reduce or block transmission), reduces economic losses, minimizes removal of important protein source for human Combination of depopulation and vaccination Vaccination efficacy in waterfowl is reduced to that seen in chikens; results in prolonged viral sheeding in ducks and subsequent spread to other species; risk of endemicity (Japan and Korea did not vaccinate and are not endemic) China : Estimated annual production of 15 billion poultry (70% smallscale farms & backyards) 35 billion doses vaccine administred from 2004 to 2007 but insufficient to cover annual production 38

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40 Stamp from the Democratic People s Republic of Korea issued in 2007 commemorating the outbreak of avian influenza among poultry. 40

41 H5N1 infection control in poultry Depopulation Poultry vaccination: reduces poultry mortality (protection of naïve birds, reduce or block transmission), reduces economic losses, minimizes removal of important protein source for human Combination of depopulation and vaccination Vaccination efficacy in waterfowl is reduced to that seen in chikens; results in prolonged viral sheeding in ducks and subsequent spread to other species; risk of endemicity (Japan and Korea did not vaccinate and are not endemic) China : Estimated annual production of 15 billion poultry (70% smallscale farms & backyards) 35 billion doses vaccine administred from 2004 to 2007 but insufficient to cover annual production 41

42 H5N1 vaccine Challenges: Handling wt viruses requires BSL3 lab wt H5N1 viruses are lethal to embryo Avian influenza HAs appear less immunogenic than human influenza HAs Co-circulation of genetically and antigenically different strains Assessment of the immune response: HI titer 40 considered as «protective» titer but actually only represents the titer at which ~50% of individuals would be protected Neutralizing titers: MN tests are not well standardized (CONCISE). Neutralizing Abs target conserved portion of the stem of the HA and by blocking fusion Non-neutralizing Abs: target epitopes on infected cells through antibody-dependent cellular toxicity 42

43 H5N1 vaccine Criteria applied by European Committee for Medicinal Products (CHMP) and FDA to assess antibody response to influenza vaccines (3 criteria to meet for pre-pandemic vaccines) 43 Baz et al. Virus Research 2013.

44 H5N1 vaccine Inactivated influenza vaccines Seed viruses generated by reverse genetics HA gene from H5N1 origin modified to remove the multibasic cleavage sire NA gene from H5N1 origin Internal proteins derived from PR8 44 Robertson & Engelhardt. Viruses 2010.

45 H5N1 vaccine Inactivated influenza vaccines Unadjuvanted inactivated split-virus and sub-unit H5N1 vaccine 2 doses of 90 µg each (Treanor et al. 2006) Ab titers decreased significantly 6 months after the 2 nd dose Adjuvanted inactivated split-virus and sub-unit H5N1 vaccines Aluminum hydroxyde or phosphate 2 doses (30 or 45 µg HA) (Nolan et al. 2008) Immune response decreased to prevaccination levels after 6 months but restored after 3rd dose (can cover 2 nd and 3rd waves during pandemics?) Oil-in-water adjuvants MF59-adjuvanted vaccine (7.5-30µg): antibody titers associated with protection after a booster dose (Stephenson et al. 2003) AS03-adjuvanted vaccine (3.8 µg): meet or exceed CHMP and FDA requirement s, up to 85% cross-reactive antibodies. Prepandrix TM (GSK) 45

46 H5N1 vaccine Egg-derived whole virus vaccine 2 dose of 10 µg with alum adjuvant: 78% seropositivity by day 42 Meet all criteria of CHMP and FDA (Lin et al. 2009) Cross reactivity in 98% and 87% of subjects against two clade 2 viruses 6 µg HA, aluminium phosphate adjuvant, single dose: Fluval H5N1 (Omninvest), licensed in Hungary Cell culture whole virion vaccine 2 doses of 7.5 µg inactivated non adjuvanted : 100% of antibodies against 4 different H5N1 viruses 46

47 H5N1 vaccine Live attenuated vaccines (LAIVs) Advantages Mimic natural infection by replicating primarely in upper respiratory tract and inducing immune response comprising mucosal IgA Potentially cheaper and quicker to manufacture than inactivated sub-unit vaccines No HA purification required Administered by intranasal drops or spray Disadvantages Not approved in all age groups Theoretical risks of reassortment with circulating influenza viruses Theoretical risks of reversion to virulence Immunogenic H5N1 LAIV development is complicate 47

48 H5N1 vaccine Live attenuated vaccines (LAIVs) Reassortant viruses bearing modified HA and NA from H5N1 coldadapted (ca) candidate virus (A/Vietnam/1203/2004) with A/Salomon Islands/3/2006 (H1N1) or A/California/7/2004 (H3N2) H5N1 ca 48 H1N1/H3N2

49 H5N1 vaccine Recombinant protein-based vaccines Baculovirus are unable to replicate in mammalian cells but can efficiently transduce a variety of mammalian cells Generate large amounts of HA proteins Only 52% of subjects developed neutralizing Abs after 2 doses of 90 µg of rha but prime-boost strategy appears interesting (Goji et al. 2008) Virus-like particles vaccines Immunologically mimic live viruses Manufactured in bulk using baculovirus and insect cells Promising results (Khurana et al. 2011) Plant-made virus-like particle vaccines HAs from different viruses cloned into vectors and expressed in Nicotina benthamiana plants (Shoji et al. 2008). Vaccines can be produced in 1 month 2 doses of 20 µg: 75% and 91% of detectable Abs by HIA and MN 49

50 H5N1 vaccine DNA vaccines Non-infectious Non-replicating Produced in large quantities using E. coli fermentation procedures Injection of plasmid directly into muscle or dermis 2 i.m injections of Vaxfectin adjuvanted plasmid H5: up to 67% of HIA titers 40 (0.5 mg injected with needle-free device) Much lower response when HA + NP + M2 plasmids are injected Adenovirus-vectored vaccines Adenoviruses selected are noncontagious, capable of infecting both dividing and nondividing cells Provide high level of expression of a gene of interest in eukaryotic target cells with integration into hos genome Able to induce both humoral and cell-mediated immunity 50

51 H5N1 vaccine Universal vaccines Targets: Extracellular portion of M2 protein (M2e) but M2e antibodies are not produced after natural infection in humans Conserved domains of HA NP Polymerase proteins Modified Vaccinia virus Ankara (MVA) vectored vaccine expressing NP and M1 gived promising results (Berthoud et al. 2011; Lillie et al. 2012) FI6: neutralizing antibody found in patient plama that recognizes the HA of 16 subtypes Research needed to find immunogens that can elicit such antibodies 51

52 H5N1 vaccine Cross-protection between H5N1 clades is extremely important Representative pre-pandemic H5N1 candidate vaccine viruses are developed by WHO Global Influenza Programme Implementation and administration of stockpiled pre-pandemic influenza vaccines could makedly reduce attack rates even the vaccine has relatively low efficacy against pandemic strain (Ferguson et al. 2006) WHO Pandemic Influenza Preparedness (PIP) framework previously included provision for a stockpile of 150 Million doses of pre-pandemic H5N1 vaccine but SAGE recommends now to stop vaccine stokpiling Need to decide which individuals would be first to be vaccinated Use of live attenuated vaccine prior to emergence of a pandemic is not prudent Remaining questions: why poor antigenicity of H5? Why rapid decay of Abs? Etc. 52

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54 THANK YOU Illegal transport of life poultry during H5N1 epidemic in Cambodia Photo taken in front of the Royal Palace, Phnom Penh, Cambodia 54