qualifying pathogens listed by the Secretary of Health and Human Services under Chapter V ( 21 U.S.C. 351 et seq.) section 505E(f). (2) Special limitation on foreign testing (A) In general No credit shall be allowed under this section with respect to any clinical testing conducted outside the United States unless— (i) such testing is conducted outside the United States because there is an insufficient testing population in the United States, and (ii) such testing is conducted by a United States person or by any other person who is not related to the taxpayer to whom the exemption under section 520(g) of Federal Food, Drug, and Cosmetic Act was granted. (B) Insufficient testing population For purposes of this section, the testing population in the United States is insufficient if there are not within the United States the number of available and appropriate human subjects needed to produce reliable and timely data from the clinical investigation. (3) Certain rules made applicable Rules similar to the rules of paragraphs (1) and (2) of section 41(f) shall apply for purposes of this section. (4) Election This section shall apply to any taxpayer for any taxable year only if such taxpayer elects (at such time and in such manner as the Secretary may by regulations prescribe) to have this section apply for such taxable year. (e) Transferability (1) In general Any taxpayer holding a credit under this section may transfer for valuable consideration unused but otherwise allowable credit for use by a qualified diagnostics research taxpayer. A taxpayer that transfers any amount of credit under this section shall file a notification of such transfer to the Secretary in accordance with procedures and forms prescribed by the Secretary. (2) Use of transferred credit Any qualified diagnostics research taxpayer that receives credit that has been transferred shall use such credit for the taxable year in which the transfer occurred. Any unused amounts of such credit may be carried back or forward to other taxable years in