Development of fda recommendations for deferral of donors based on risk of bse exposure
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Development of FDA Recommendations for deferral of donors based on risk of BSE exposure. Alan E. Williams, Ph.D. Director, Division of Blood Applications Office of Blood Research and Review CBER, FDA TSE Advisory Committee October 14, 2004. Goals:.

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Development of FDA Recommendations for deferral of donors based on risk of BSE exposure

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Development of fda recommendations for deferral of donors based on risk of bse exposure

Development of FDA Recommendations for deferral of donors based on risk of BSE exposure

Alan E. Williams, Ph.D.

Director, Division of Blood Applications

Office of Blood Research and Review

CBER, FDA

TSE Advisory Committee

October 14, 2004


Goals

Goals:

  • Effective response to the spread of vCJD in Europe and the potential threat to blood safety

  • Optimal balance between vCJD risk reduction and blood supply preservation

  • Implementation plan that is sensitive to the dynamics of donor recruitment and blood resource sharing

  • Coherent and uniform national policy


Empirical vcj d risk model

“Empirical ” vCJ-D Risk Model

  • Likelihood of dietary exposure

  • Length of incubation period (mean and range)

  • Prevalence of asymptomatic carrier state

  • Presence of vCJD agent in blood during incubation period/carrier state

  • Susceptibility of recipient population

     VERY LIMITEDDATA, THEREFORE ANEMPIRICAL MODEL IS NOT POSSIBLE


Linear vcjd risk model

“Linear” vCJD Risk Model

Risk of exposure to BSE/vCJD is linear and related to the duration and likelihood of dietary exposure

  • Concept previously endorsed by TSEAC

  • Assumptions

    Data regarding travel and residence in BSE-endemic country

    is a valid surrogate for:

    • dietary exposure to BSE

    • subsequent potential to transmit vCJD via blood


1999 blood donor travel survey

1999 Blood Donor Travel Survey

  • Probability sample of accepted donors at twelve blood center sites - Winter, 1999.

  • 19,067 surveys - single page mailing with cover letter

  • 9,541 anonymous responses (~ 50%)

  • UK (European) travel, sex, age, FT/Rpt, education

  • Data requested by TSEAC and presented extensively at previous meetings.

    Note: Donor survey estimates are reproducible, but are based upon self-report and have not been validated by other independent measures. Short survey - numerous data extrapolations.


Any blood donor travel residence uk and any european country with endemic bse in 1999

Any Blood Donor Travel/Residence: UK and any European Country with endemic BSE in 1999

  • Any UK Travel/residence 1980-1996 - 22.8%

    Range by blood center - 10.2 - 31.7%

    Higher travel with education, age, repeat status

  • Any European country with BSE in 1999 - 35.5%


Possible donor exposures to bse vcjd

Possible Donor Exposures to BSE/vCJD

  • Person-Days Exposure - Derived from total estimated cumulative time spent by donors in a defined geographic area

  • Donor loss - Estimated proportion of donors who spent time in a geographic area  cut-off value


Blood supply concerns

Blood Supply Concerns

  • Blood Donor base

    • ~80% repeat donors (deferrals costly)

    • Stressed by changing donor demographics and deferrals related to donor exposures and test results.

      Aging

    • Fewer large worksite collections

  • Elasticity of Supply

    • 3-5 % maximum donation loss experience

      (1986 anti-HBc; 2000 ear/finger stick + UK deferral)

    • Limited supply during Summer and holidays (esp. 2002)

  • Public responds to appeals - long term impact uncertain

  • Capability of monitoring supply impact


Uk bse exposure donor loss analysis based upon 252 804 total uk person days exposure

UK BSE Exposure/Donor LossAnalysis (Based upon 252,804 total UK person-days exposure)

UK 6 month deferral

UK p-d removed: 217,411/252,804 (86.0%)

Residual total p-d: 35, 393 (14.0%)

Donor loss: 2.2%

% p-d removed/1% donor loss: 39.1


Bse exposure donor loss analysis

BSE Exposure/Donor Loss Analysis

UK 3 months de novo

UK p-d removed: 235,866/252,804 (93.3%)

Residual total p-d: 16,938/252,804 (6.7%)

Donor loss: 3.4%

% p-d removed/1% donor loss: 27.4


Bse exposure donor loss analysis1

BSE Exposure/Donor Loss Analysis

UK 1 month de novo

UK p-d removed: 245,978/252,804 (97.3%)

Residual total p-d: 6826/252,804 (2.7%)

Donor loss: 6.4%

% p-d removed/1% donor loss: 15.2


Bse exposure donor loss analysis2

BSE Exposure/Donor Loss Analysis

UK 1 month, given 3 month UK deferral

Additive UK p-d removed (based on total):

10,112/ 252,804 (4.0%)

Total p-d removed: 245,978/304,406 (97.3%)

Residual total p-d: 6826/252,804 (2.7%)

Addl. donor loss: 3.0%

% residual p-d removed /1% donor loss: 1.3


Development of fda recommendations for deferral of donors based on risk of bse exposure

Residual vCJD Risk (Theoretical) vs.

Percent of Blood Supply Lost


Development of fda guidance issued november 1999

Development of FDA Guidance issued November, 1999

  • June 2, 1999 TSEAC

  • Guidance to Industry November 11, 1999

    • Donor deferrals undertaken concurrent with a commitment to monitor the blood supply (estimated loss 2%)

    • Donor deferrals recommended for:

      • travel/residence in U.K. for >six months between 1980- 1996

      • Receipt of bovine insulin sourced in the U.K. after 1980

    • Product retrieval recommended if donor later discovered to have vCJD


Estimation of potential bse vcjd risk remaining after november 1999 guidance implementation

Estimation of Potential BSE/vCJD Risk Remaining After November, 1999 Guidance Implementation


Fda cdc weighted linear risk model for estimating possible donor exposure to bse vcjd

FDA/CDC “Weighted“ Linear Risk Model for Estimating Possible Donor Exposure to BSE/vCJD

Risk weighted by geographic exposure based on observations of UK beef imports, vCJD cases, and indigenous BSE

UK = 1.0Epidemic focus, index country

France = 0.05UK beef imports; obs. BSE, vCJD

Other Europe (incl. Euroblood) = 0.015

Indigenous BSE, uncertain surveillance, reporting, food controls

(Note: Travel/residence in France calculated as ~ 0.7 UK based on overall travel prevalence)


Fda cdc weighted linear risk model for estimating possible donor exposure to bse vcjd1

FDA/CDC “Weighted“ Linear Risk Model for Estimating Possible Donor Exposure to BSE/vCJD

DoD active duty and dependents stationed onEuropean bases = 0.35

(US bases supplied with ~ 35% UK beef)


Development of revised fda guidance issued january 2002

Development of Revised FDA Guidance issued January, 2002

  • June 18-19, 2001 TSEAC

  • Guidance to Industry January, 2002 (deferrals)

    > 3 months residence/travel in U.K. 1980 - 1996

    > 5 years residence/travel in Europe

    • For donors of Source Plasma this criterion applies only to France (5-10% consumption of UK beef)

      > 6 months on certain US military bases in Europe between 1980-1990 or 1980-1996 (up to 35% UK beef consumed)

      Transfusion in the U.K. 1980 – present

      Receipt of bovine insulin sourced in the U.K. after 1980


Estimated further bse vcjd risk reduction following implementation of january 2002 revised guidance

Estimated Further BSE/vCJD Risk Reduction Following Implementation of January, 2002 Revised Guidance

Option #3 (FDA)

Current Risk reduced 72 %

(Total Risk Reduced 91%)


Revised fda guidance issued january 2002

Advantages:

Deferral tied to BSE observational data. Ratio of 3 mo. (UK) to 60 mos. (Europe) reflects “worst case” 5% European dietary estimate relative to UK . (3 mo. deferral for all of Europe in absence of weighting would add additional 7-8% donor loss)

Impact on NY area blood supply was severe, but was expected to be modulated by lesser impact elsewhere in US

Pilot provision allows flexibility for stricter policies

Some protection for human-human passage of vCJD

Recognizes food chain protections

Revised FDA Guidance issued January, 2002


Revised fda guidance issued january 20021

Disadvantages:

At the time, transfusion-transmission of vCJD was theoretical

Donor screening questions are complex

Estimated 4-6% US donor loss exceeded past experience. Ability of rest of US to compensate for severe impact in NY area was untested.

Revised FDA Guidance issued January, 2002


Observed impact of 2002 guidance on us donor base

Observed Impact of 2002 Guidance on US Donor Base

  • BSE/vCJD Deferrals phased in during May and October, 2002

    • Projected loss 5.0% nationwide

    • Actual loss not directly measurable

    • Major component of industry more restrictive

  • Disproportionate impacts of travel deferrals

    • Coastal cities: 50%  donor loss (e.g. NYC and SF)

    • Rural US: 50%  impact

    • New York area “Euroblood” lost by pan-European deferral

    • Military bases

    • TSEAC requested supply monitoring and assessment

  • Seasonal and regional blood shortages persist


Potential future challenges

Potential Future Challenges

  • Recent documentation of transfusion-transmission during vCJD asymptomatic incubation period

  • Deferral for UK transfusion in 2001 was precautionary

    • Additional deferral of individuals with previous transfusion? (adaptation of vCJD agent)


Estimated donor loss related to history of transfusion in uk france and europe

Estimated Donor Loss Related to History of Transfusion in UK, France and Europe

  • Assumptions:

    • 5% prevalence of transfusion in US donors overall (REDS data)

    • >/= 5 yr travel/residence CONSERVATIVELY approximates lifetime transfusion exposure

    • rate of tx among long term residents/travelers to Europe and UK = overall US donor prevalence

    • prevalence of travel to France = 0.7 x travel to UK

  • Hx tx (UK - deferral already accomplished) 0.4 x 0.05 = 2/10,000

  • Hx Tx (any Europe, excl. UK) 0.7% x 0.05 = 3/10,000

  • Hx Tx (France) 0.4 x 0.7 x 0.05 = 1.4/10,0000


Spread recognition of bse vcjd in new geographic areas

Spread/Recognition of BSE/vCJD in New Geographic Areas

  • No exposure data available for donors beyond UK and European BSE Countries

  • Despite limitations, survey data provided a framework for risk:donor loss estimates

  • TSEAC may wish to consider new data collection efforts that will support future deliberations


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