Antivirals for Pandemic Influenza Frederick G. Hayden, MD Division of Infectious Diseases and International Health University of Virginia School of Medicine Charlottesville, Virginia, USA

Antiviral Agents For Influenza Class/agentBrand nameRoute M2 inhibitors AmantadineSymmetrelPO RimantadineFlumadinePO NA inhibitors Zanamivir (GG167)RelenzaInhaled Oseltamivir (GS4104)TamifluPO Peramivir (BCX-1812)*PO/IV/IM *Investigational at present in USA.

Chemoprophylaxis

Amantadine Prophylaxis During Pandemic Influenza Hayden. J Infect Dis. 1997;176:S56. Protective Efficacy PandemicInfluenza A illnessSeroconversion 1968 H3N %28-52% 1977 H1N131-71%19- 39%

Projected Outbreak of H5N1 in Thailand Red = new cases. Green = areas where the epidemic has finished. Ferguson et al. Nature. Published online. August R 0 = 1.5

Projected Outbreak of H5N1 Influenza in Thailand Left: uncontrolled outbreak. Red = new cases. Green = areas where the epidemic has finished. Above: Controlled outbreak. Red = areas of infection. Blue = areas where a combination of control measures implemented.

Elimination of a Pandemic Virus at its Source? Ring chemoprophylaxis feasible if: –Geographically targeted in non-urban setting –Early intervention within 1-3 weeks –Virus of low-moderate transmissibility (R 0 < 1.8) –Chemoprophylaxis of % of population –High compliance –Movement restrictions; social distancing Maximum of 1-3 million courses needed –300,000 may be sufficient Ferguson et al. Nature. published online, August 2005.

Efficiency of Pandemic Antiviral Use No. persons Antiviral strategy Percent on drug Duration (days) Total doses needed 1,000Prophylaxis100%5656,000 1,000Treatment 35% 5 3,500

Efficiency of Pandemic Antiviral Use No. persons Antiviral strategy Percent on drug Duration (days) Total doses needed 1,000Prophylaxis100%5656,000 1,000Treatment 35% 5 3, fold .

Treatment

Nasal Aspirate Viral Detection in Hospitalized Children: Effect of NAI Treatment Influenza virus Antiviral Tx No.Duration of fever (hrs) Days of Detection AntigenCulture A/H3N2None Oseltamivir Zanamivir BNone Oseltamivir Zanamivir * *P<0.5 versus no treatment. Mean ages 3.1 – 6.7 years across groups Sato et al. Ped infect Dis J. 2005;24:931.

Oseltamivir and Complications in ILI: Retrospective Cohort Study, USA, Outcome < 30 days Oseltamivir (N = 39,202) Untreated (N = 136,799) Adj. Hazard Ratio (95% CI) Pneumonia0.9%1.5%0.68 (0.63, 0.73) Myocardial infarction 0.1%0.3%0.33 (0.10, 1.07) Death from any cause 0.003% (N = 1) 0.042% ( N = 56) 0.09 (0.01, 0.65) Nordstrom et al. 2nd Euro Influenza Conf, abst no. S18-2, 2005.

Estimated Pandemic Mortality, Gani et al. Emerging Infect Dis. 2005;11:1355. Estimated Deaths per 100, 000 population No Treatment 20% stockpile – treat all groups 10% stockpile – treat all groups Week no

H5N1 Virus

Oseltamivir in Experimental A/HK/156/97 (H5N1) Infection of Mice Leneva et al. Antiviral Res. 2000;48:101. Dose: 1mg/kg/d Percent of Survivors Days After Infection hours before infection 24 hours delay 36 hours delay 48 hours delay 72 hours delay control x x x x x x x

Oseltamivir for A/Vietnam/1203/04 Virus in Mice Days After Inoculation mg/kg/day 1 mg/kg/day 0.1 mg/kg/day placebo B 8-Day Treatment Survival Distribution Function Days After Inoculation A 5-Day Treatment Yen et al. JID. 2005;192:665.

Sensitivity of Reverse Genetic-Derived Influenza Viruses to Neuraminidase (NA) inhibitors (NAIs) in NA-inhibition and Virus-reduction Assays IC 50, nmol/LEC 50, µmol/L Reverse-genetics virusZanamivir Oseltamivir carboxylate Zanamivir Oseltamivir carboxylate VN1203 x PR8 (H1N1)0.8 ± ± ± ± 0.1 HK 156 PR8 (H1N1)0.7 ± ± ± ± 0.1 PR/8/34 (H1N1)0.7 ± ± ± ± 1.2

Oseltamivir Therapy in H5N1: Thailand and Vietnam, Oseltamivir Treatment No. Patients No. (%) Survivors Yes256 (24%) No123 (25%) Writing Committee. NEJM. 2005;353:1374.

Oseltamivir Treatment Failure in H5N1 Late initiation- pulmonary injury Primary infection → sustained replication Altered pathogenesis –Viral virulence factors –Extra-pulmonary dissemination –Pro-inflammatory host immune responses Inadequate dose regimen –Inadequate absorption (diarrhea, GI dysfunction) Antiviral resistance emergence

Amantadine Therapy in H5N1: Hong Kong, 1997 Amantadine treatment No. patients No. (%) survivors Yes < 5 days > 6 days (60%) 4 (100%) 2 (33%) No 8 6 (75%) K-Y Yuen, personal communication.

Pharyngeal Viral Loads during Oseltamivir Treatment of H5N1 de Jong et al. NEJM. 2005;353:25. Complementary DNA (log copies/ml of viral-tran sport medium) Days Since Admission Patient 1, died Patient 2, died Patient 3, died Patient 4, died Patient 5, survived Patient 6, survived Patient 7, survived Patient 8, survived Oseltamivir- resistant Oseltamivir-therapy

Antiviral Resistance

Antiviral Resistance to M2 Inhibitors in Community Isolates of A/H3N2, Bright et al. 2nd Euro Influenza Conf Lancet. pub online Sept 22, %

Antiviral Research 49 (2001)

Oseltamivir Resistance, Japan, Single season survey of NAI resistance –~ 6M treatment courses (or ~5% of population) –Outpatient isolates from 74 public health labs –Phenotypic susceptibility by NAI assay 3/1,180 (0.3%) of influenza A (H3N2) isolates resistant –2 E119V, 1 A292K Very low frequency of resistance in community isolates despite substantial oseltamivir use –Likely due to low-level transmission of resistant variants and not primary NA inhibitor resistance Neuraminidase Inhibitor Susceptibility Network. WHO Weekly Epi Record. April 29, 2005.

Oseltamivir Resistance In N1 Neuraminidase Single nucleotide substitution (His274Tyr) →↓oseltamivir susceptibility (≥ 400–fold) Frequency drug therapy of H1N1: –H1N1: children 16% (7/43), adults 4% (2/50) –H5N1: 2/8 (25%) Reduced replication in cell culture (> 2.0 log 10 ) –↓infectivity in mouse (1,000-fold) and ferret (>10-fold) –Variable ↓ pathogenicity in ferret Transmissible in ferret model Ives et al. Antiviral Res. 2002;5:307. Herlocher et al. JID. 2004;190:1627.

Oseltamivir-Susceptible and Resistant H5N1 in Ferrets: Effect of His274Tyr Mutation Le et al. Nature Oseltamivir – resistant, mock treated Oseltamivir – sensitive, mock treated Days Postinfection 0 ≤

NA Inhibitor Resistance Profiles NA mutation NA type/ subtype Susceptibility in the NAI assay (fold  ) OseltZanaPeramA E119VA/N2R (>50)S (1) R292KA/N2R (>1000)S (4-25)R (40-80)S (8) H274YA/N1R (>700)S (1)R (40-100)S (3) R152KBR (>30-750)R (10-100)R (>400)R (150) Mishin et al. AAC. 2005;49:4516. Wetherall et al. AAC. 2003;41:742.

Oseltamivir-Rimantadine for A/Qa/HK/G1/97 (H9N2) in Mice Percent Survival (day 14) Oseltamivir dose (mg/kg/d) Leneva et al. Antiviral Research. 2000;48:101.

Investigational Anti-Influenza Agents Neuraminidase (NA) inhibitors –Peramivir (oral/IV), A (oral) Long-acting NA inhibitors (LANI) –R (topical), Flunet  (topical) Conjugated sialidase –Fludase™ (topical) HA inhibitors- cyanovirin-N Polymerase inhibitors –siRNA; ribavirin (aerosol/IV/PO); T-705; viramidine Protease inhibitors –Aprotinin

IV Peramivir in Influenza A/duck/MN/1525/81(H5N1) Infection in Mice DrugRoute Dose (mg/kg) Survival (N=10) Days to death (mean + SD) PeramivirIV30 x 1100%*>21* IV10 x 1100%*>21* IV3 x 150% Oseltamivir CarIV20 x 160% OseltamivirPO10 bid x 5 d70% SalineIV--45% * P<0.01 compared to saline controls Barnard et al. Presented at Second International Conference on Community Acquired Pneumonia, Montreal, Sept 17-19, 2005.

Antivirals for Pandemic Influenza: Conclusions M2 inhibitors have proven efficacy in pandemic influenza and are a less costly option for prophylaxis if virus is susceptible Targeted geographic NAI prophylaxis might succeed in containing the emergence of a pandemic under certain conditions If available in sufficient time (rapid distribution) and quantities (stockpiling), NA inhibitors could provide substantial benefits in pandemic influenza

Antivirals for Pandemic Influenza: Conclusions Oseltamivir-resistant N1 variants due to H274Y emerge during Rx but are less fit and retain susceptibility to zanamivir Concerns about NA inhibitor resistance should not be a deterrent to stockpiling decisions Need exists for alternative agents/approaches –An injectable NAI is needed, especially one with activity for oseltamivir-resistant variants –Combinations of antivirals and of antivirals and host immune response modifiers warrant study