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Validation of Nucleic Acid and Serological Tests to Screen Blood and Plasma donors for Acute infection with West Nile virus. Hira Nakhasi, Ph.D. Director, DETTD/OBRR CBER, FDA. Issue. FDA seeks advice on:

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Validation of Nucleic Acid and Serological Tests to Screen Blood and Plasma donors for Acute infection with West Nile virus

Hira Nakhasi, Ph.D.

Director, DETTD/OBRR

CBER, FDA

issue

Issue

FDA seeks advice on:

The design of scientific studies needed to validate NAT and possibly IgM for WNV as blood donor screening tests

Whether available data on clearance of viruses in the manufacture of plasma derivatives are sufficient basis to obviate screening of Source Plasma donations

Whether Strategies to limit screening to particular locations and time are appropriate

background information

Background Information

WNV is an enveloped single stranded RNA virus

WNV is a mosquito-borne falvivirus

Primarily infects birds

Occasionally infects humans and other animals

About 80% of human infection is asymptomatic, and 20% develop mild febrile illness (flu-like illness)

Approximately 1 in 150 infections results in meningitis or encephalitis

Advanced age is by far the most significant risk factor for severe neurologic disease

Viremic period can occur up to 2 weeks prior to symptoms and last up to a month from the initiation of the infection

background information4

Background Information…….

The 2002 US outbreak of WNV resulted in the identification of other modes of transmission including:

Blood transmission, Transplantation, Breast-feeding, Transplacental and Occupational by percutaneus injury

The magnitude of the risk of WNV from transfusion is unknown.

Virus titer in blood is low compared to other transmissible viruses (~1-5x103 copies/ml) and the viremia is transient.

Viremia in encephalitis patients can be as high as 2.5x106 copies/ml

Viremia resolves rapidly after seroconversion to IgM

IgM can persist for a long time in some cases up to a year

No chronic stage of WNV infection has been reported

current status of wnv pathogenicity and epidemiology in the us

Current status of WNV pathogenicity and epidemiology in the US

In year 2002 total number of WNV cases reported were 4008 out which 263 deaths and 2741 cases of WNME

39 states including DC is endemic for WNV

Estimated risk of 1.8-2.7 infections per 10,000 donations nation wide but can be high in endemic regions (16/10,000 with a mean of 6-8/10,000)

During Aug 28, 2002-Jan 3, 2003, 61 possible Transfusion-Transmitted cases reported

21 are confirmed from 14 blood donations

19 are not transfusion related,

21 are under investigation

west nile virus and blood safety fda s actions to date
West Nile Virus and Blood Safety: FDA’s Actions to Date
  • Alert notices posted on FDA’s website:
    • August 17, 2002: Vigilance in excluding symptomatic donors urged prior to any actual report of transmission
    • October 3, 2002: FDA states its interest in facilitating development of donor screening & supplemental tests
  • Congressional hearings on September 10 & 24, and October 3, 2002
  • FDA issued a guidance on “ Current thinking on management of donors and products” (www.fda.gov/cber/gdlns/wnvguid.htm), Oct. 2002
  • Cooperation with CDC, State Public Health Departments, Blood Organizations and Health Resources and Services Administration (HRSA)
    • Epidemiological investigation of all possible cases of transfusion transmitted WNV
    • Advice provided on deferral of donors and withdrawal of in-date products collected from suspect donors
wnv workshop held in nov 02

WNV workshop held in NOV ‘02

Following topics were discussed:

Methodologies suitable for donor screening

Proposed studies on prevalence in donors

FDA and industry perspective on developing WNV assays

Strategies aimed at inactivation of WNV in plasma derivatives

Implementation issues

Summarized at the December 2002, BPAC meeting

regulatory pathways for assay development
Regulatory Pathways for Assay Development
  • Donor screening and supplemental tests will be reviewed as biologic products under the PHS Act
    • IND Applications are needed
    • Biological License Applications for pre-market approval
  • The instrument and software portion of the application requires a separate 510(k) submission. (See: CDRH Guidance for the Content of Pre-market Submissions for Software Contained in Medical Devices.)
    • A licensed test used for screening blood donors has been determined to be a “major level of concern.”
regulatory pathway for wnv blood and plasma donor testing

Regulatory Pathway for WNV Blood and Plasma Donor Testing

Approval Mechanism

Clinical and analytical sensitivity, specificity

CMC

Reproducibility, Stability

Instrumentation and software

Clinical Study Design

Validation of Clinical Sensitivity of NAT and IgM assays

Validation of Clinical specificity of NAT and IgM assays

Approaches for test validations in the absence of reference assays

Reproducibility studies

regulatory pathway for wnv blood and plasma donor testing10

Regulatory Pathway for WNV Blood and Plasma Donor Testing………..

Unit and Donor Management

Algorithms for identifying reactive samples

Confirmation and follow up of reactive samples

Guidance for donor deferral

Product quarantine

Product retrieval

cber fda s efforts towards the development of wnv screening tests
CBER/FDA’s efforts towards the development of WNV screening tests
  • Development of Reference Panels for lot release testing
    • Panels to be tested by several laboratories in a collaborative study
  • Development of Qualification panel of well-characterized and pedigree specimens
    • Establish relative sensitivity of NAT and IgM assays
  • Development of in-house TaqMan PCR and IgM test for WNV Using in-house primers
    • Distribution in the blood components
    • Infectious dose
    • Viral tropism
review of methodologies that are suitable for blood and source plasma donor screening

Review of methodologies that are suitable for blood and Source Plasma donor screening

Nucleic acid based tests (NAT):

Whole Blood

Source Plasma

Supplemental tests

Serological (IgM assays):

Whole blood

Source Plasma

Supplemental tests

review of proposed studies on prevalence in donors
Review of proposed studies on prevalence in donors
  • Development of analytical sensitivity panels
  • Comparison of WNV RNA and IgM assays
  • Prevalence of viremia (viral load, IgM antibody, virus culture status)
  • Comparison of MP vs ID- NAT
  • Confirm donor viremia by IgM and RNA testing of donor follow up sample
  • Assess disease outcome in Viremic donations, routine “call back” information
  • Establish back ground community-acquired WNV exposure rates
  • WNV incidence and transfusion-transmission rates
  • Exposure rates in recipients by testing autologous donations for IgM reactivity
  • Status of proposed studies on prevalence in donors (presentation by CDC, REDS group and ARC)
testing source plasma donors and clearance of wnv from plasma derived products

Testing Source Plasma Donors and Clearance of WNV from Plasma-Derived products

Testing of Source Plasma donations

Identifying positive units

Reduction of viral load in the manufacturing pool

Inclusion of viral clearance (inactivation and /or removal) steps in the manufacturing processes

Product specific

Process-specific

Model viruses

WNV specific

implementation of wnv donor test
Implementation of WNV donor test
  • Blood supply management and triggers for WNV testing in the event the test is not available at the time of epidemic
  • Other implementation issues for WNV testing:
    • Seasonal vs Year round
    • Geographical vs National
    • Need for testing related viruses
    • ID NAT vs minipool NAT
    • Past experiences from SLE epidemic
questions for the committee
Questions for the committee
  • Q.1 Please comment on FDA’s proposed criteria for validation of WNV NAT and IgM assays for donor screening.
  • Q.2. Do the committee members agree that product and process-specific clearance of the WNV agent (as opposed only to marker viruses) should be demonstrated in order to adequately assure the safety of plasma derivatives?
  • Q.3. Do the committee members agree that screening of all plasma for fractionation for WNV would add a safety margin in the manufacture of plasma derivatives?
  • Please comment on the scientific validity of possible strategies to limit WNV screening to particular locations and times depending on epidemic surveillance information and test availability.