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Risk assessment: The Safety of Blood Products presented by Dr. Thomas R. Kreil Baxter BioScience on behalf of the PPTA Pathogen Safety Steering Committee Technical meeting with FDA April 29, 2003
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29.04.03 2 The safety of blood products Risk assessment considerations – Plasma viremia – Infectious virus titer of positive units – Prevalence of viremia in the population – Resulting plasma manufacturing pool loads – Reduction by manufacturing processes – Further relevant features
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29.04.03 3 Symptomatic Individuals – 10 2 – 10 5 iu/ml: in patients with underlying malignant disease CM Southam & AE Moore, Am J Trop Med Hyg [1951] 31: 724 – 2.5 x 10 6 c/ml: 3 days after onset of neurological symptoms C Huang et al., http://www.cdc.gov/ncidod/EID/vol8no12/02-0532.htmhttp://www.cdc.gov/ncidod/EID/vol8no12/02-0532.htm Otherwise Healthy Donors – 1-5 x 10 3 c/ml: FDA BPAC briefing package, March 13, 2003 – 2 x 10 5 c/ml: 1 in 7,107 (out of samples 75% targeted for risk ) A Conrad / NGI, BPAC March 13, 2003 worst case: 2 x 10 5 PCR copies/ml West Nile Virus - Viremia
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29.04.03 4 Infectious virus titer of positive units – Mean PCR detectable amount of virus: 0.00289 pfu/mL (0.001640 – 0.005099 pfu/mL) A Conrad / NGI, BPAC March 13, 2003; CDC WNV panel (Lanciotti) – Assuming that already ONE copy is PCR detectable: 1 infectious virus particle per 346 (196-610) genomes – Viremia of max. 2x10 5 PCR detectable genomes, at only 1 infectious particle per 196 genomes: worst case: max. 1,020 infectious units per ml West Nile Virus
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29.04.03 5 Prevalence of viremia in the population Modeling approach – US average risk: 0.36 per 10,000 donors – US maximum risk: 1.55 per 10,000 donors (peak epidemic) – Michigan: about 4 per 10,000 donors (during the epidemic) – Michigan: about 10 per 10,000 donors (peak epidemic, Sept 1) – Detroit: up to 20 per 10,000 donors (peak epidemic, Sept 1) Dr. Lyle Petersen / CDC: BPAC, March 13, 2003 http://www.fda.gov/ohrms/dockets/ac/03/transcripts/3940t1.htm West Nile Virus
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29.04.03 6 Verification by testing (viremia study) – Samples from Cleveland and Detroit: i.e. highest risk areas – Obtained during the first three weeks of September 2002: i.e. highest risk period – model: estimated risk ~ 8.2 per 10,000 in that population. – TaqMan PCR: 6 / 5,761 samples positive, i.e. viremia prevalence: worst case: 10.4 per 10,000 Dr. Sue Stramer / ARC: BPAC, March 13, 2003 http://www.fda.gov/ohrms/dockets/ac/03/transcripts/3940t1.htm Prevalence of viremia in the population West Nile Virus
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29.04.03 7 Max. viremic donor prevalence: 10.4 per 10,000 i.e. approx. 1 per 1,000 Max. viremia levels: 1,020 infectious units / ml Dilution of viremic donations into manufacturing pools: maximum of 1 infectious unit per ml, assuming the highest potential load, and the highest prevalence WORST CASE (earthquake during a hurricane) Resulting plasma pool loads West Nile Virus
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29.04.03 8 Plasma viremia: 1-5 x 10 3 c/ml (FDA BPAC info) assume mean of 3,000, statistically Infectious virus titer of positive units: ~10 units/ml 1 infectious virus particle per 346 genomes, i.e. mean of determined range Prevalence of viremia in the population: 2/10,000 average risk throughout the U.S., during peak epidemic Resulting plasma manufacturing pool loads: ~0.001 units/ml PLUS: reduction by manufacturing processes ! Base case West Nile Virus
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29.04.03 9 WNV would be below the limit of detection for current virus assays Inconsistent with current practice for HIV, HCV and HBV Resulting plasma pool loads West Nile Virus
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29.04.03 10 ALL dedicated virus inactivation steps which have been investigated so far resulted in complete inactivation of WNV reduction factors ranging between >5.5 and >8.2 very rapid inactivation kinetics of WNV verification of the fact that WNV behaves exactly like predicted from model virus (BVDV, TBEV) data !! Reduction by manufacturing processes West Nile Virus
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29.04.03 11 Besides dedicated virus inactivation steps, other steps contribute to virus reduction during manufacturing process. – only dedicated steps considered For manufacturing process, the overall virus reduction capacity is determined by a combination of virus inactivation and virus removal. – only inactivation investigated Reduction by manufacturing processes ? West Nile Virus
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29.04.03 12 Acute self-limiting infection: life-long test-based donor deferral is only prudent for chronically-infected persons No medical benefit to the donor No public health benefit from WNV testing Further relevant features West Nile Virus
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29.04.03 13 Conclusions: Donation loads below limit of detection for current test strategies Typical flavivirus characteristics Effective viral reduction by existing processes West Nile Virus
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