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  <xs:element id="bcrx_AggregateLeaseExpense" abstract="false" name="AggregateLeaseExpense" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_PercentageOfCommonStockSharesBeginning" abstract="false" name="PercentageOfCommonStockSharesBeginning" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="bcrx_IncentivePlanAndInducementPlanMember" abstract="true" name="IncentivePlanAndInducementPlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_NoncashInterestExpenseAndAmortizationOfDebtIssuanceCosts" abstract="false" name="NoncashInterestExpenseAndAmortizationOfDebtIssuanceCosts" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_AnnualNetSalesBetween15And3BillionsMember" abstract="true" name="AnnualNetSalesBetween15And3BillionsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_LongTermInvestmentMaturityMinimum" abstract="false" name="LongTermInvestmentMaturityMinimum" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="bcrx_AverageMaturityPeriodOfHighQualityMarketableSecurities" abstract="false" name="AverageMaturityPeriodOfHighQualityMarketableSecurities" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="bcrx_RPI2019IntermediateFinanceTrustMember" abstract="true" name="RPI2019IntermediateFinanceTrustMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_VestUponSuccessfulCompletionOfSpecificDevelopmentMilestonesMember" abstract="true" name="VestUponSuccessfulCompletionOfSpecificDevelopmentMilestonesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_RoyaltyReceivableMember" abstract="true" name="RoyaltyReceivableMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_PotentialMilestonePaymentsReceivableIfRegulatoryApprovalBeforeMilestone" abstract="false" name="PotentialMilestonePaymentsReceivableIfRegulatoryApprovalBeforeMilestone" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_RoyaltyExpenseReversalOfExpense" abstract="false" name="RoyaltyExpenseReversalOfExpense" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_ASPRBARDAContractMember" abstract="true" name="ASPRBARDAContractMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_RoyaltyPaymentsReceivableExpirationTermFromFirstCommercial" abstract="false" name="RoyaltyPaymentsReceivableExpirationTermFromFirstCommercial" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="bcrx_RoyaltyPurchaseAgreementRoyaltiesPercentageOfAnnualNetSalesBasedOnReductionInSales" abstract="false" name="RoyaltyPurchaseAgreementRoyaltiesPercentageOfAnnualNetSalesBasedOnReductionInSales" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="bcrx_BetweenTheSecondAndThirdAnniversariesMember" abstract="true" name="BetweenTheSecondAndThirdAnniversariesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_DebtCovenantTermsAxis" abstract="true" name="DebtCovenantTermsAxis" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType"/>
  <xs:element id="bcrx_DebtCovenantTermsDomain" abstract="true" name="DebtCovenantTermsDomain" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_MaturityPeriodOfHighQualityMarketableSecurities" abstract="false" name="MaturityPeriodOfHighQualityMarketableSecurities" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="bcrx_RoyaltyFinancingObligationsTableTextBlock" abstract="false" name="RoyaltyFinancingObligationsTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="bcrx_RoyaltyMonetizationsLineItems" abstract="true" name="RoyaltyMonetizationsLineItems" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="bcrx_JPRRoyaltySubLLCMember" abstract="true" name="JPRRoyaltySubLLCMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_BaseContractMember" abstract="true" name="BaseContractMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_AnnualNetSalesRangeDomain" abstract="true" name="AnnualNetSalesRangeDomain" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_TermLoanAAndBDrawnMember" abstract="true" name="TermLoanAAndBDrawnMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_RPI2021And2020IntermediateFinanceTrustMember" abstract="true" name="RPI2021And2020IntermediateFinanceTrustMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_MaximumAggregateOfferingPrice" abstract="false" name="MaximumAggregateOfferingPrice" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_TermBLoanMember" abstract="true" name="TermBLoanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_TransactionCosts" abstract="false" name="TransactionCosts" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_AfterFourthAnniversaryMember" abstract="true" name="AfterFourthAnniversaryMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_FutureRoyaltiesPayable" abstract="false" name="FutureRoyaltiesPayable" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_AnnualNetSalesUnder350000Member" abstract="true" name="AnnualNetSalesUnder350000Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_CommonStockPurchaseAgreementWithRPIMember" abstract="true" name="CommonStockPurchaseAgreementWithRPIMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_ScheduleOfReceivablesFromCollaborationsTableTextBlock" abstract="false" name="ScheduleOfReceivablesFromCollaborationsTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="bcrx_NonCashInterestExpenseOnRoyaltyFinancingObligation" abstract="false" name="NonCashInterestExpenseOnRoyaltyFinancingObligation" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_AnnualNetSalesRangeAxis" abstract="true" name="AnnualNetSalesRangeAxis" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType"/>
  <xs:element id="bcrx_TermCLoanMember" abstract="true" name="TermCLoanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_AnnualNetSalesOver550000Member" abstract="true" name="AnnualNetSalesOver550000Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_TradeReceivablesTextBlock" abstract="false" name="TradeReceivablesTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="bcrx_SharesIssuedCommonStockPremium" abstract="false" name="SharesIssuedCommonStockPremium" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_TermALoanMember" abstract="true" name="TermALoanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_SharesIssuedPricePerSharePremium" abstract="false" name="SharesIssuedPricePerSharePremium" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="bcrx_MilestonePaymentMaximum" abstract="false" name="MilestonePaymentMaximum" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostExpectedToBeRecognizedYearThree" abstract="false" name="EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostExpectedToBeRecognizedYearThree" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_CreditAgreementMember" abstract="true" name="CreditAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_ThirtysixEqualMonthlyInstallmentsMember" abstract="true" name="ThirtysixEqualMonthlyInstallmentsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_RoyaltyMontizationsRollForward" abstract="true" name="RoyaltyMontizationsRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="bcrx_OperatingLeaseRightOfUseAssetAccumulatedAmortization" abstract="false" name="OperatingLeaseRightOfUseAssetAccumulatedAmortization" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_FutureRoyaltiesPayableMember" abstract="true" name="FutureRoyaltiesPayableMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_TermLoanADrawnMember" abstract="true" name="TermLoanADrawnMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_ORLADEYOMember" abstract="true" name="ORLADEYOMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_CollateralForCreditMember" abstract="true" name="CollateralForCreditMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_BetweenTheThirdAndFourthAnniversariesMember" abstract="true" name="BetweenTheThirdAndFourthAnniversariesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_InterestAndOtherIncomeLoss" abstract="false" name="InterestAndOtherIncomeLoss" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_DebtSecuritiesAvailableforsaleFairValueMaturityAllocatedAndSingleMaturityDateAfterYearOneThroughTwo" abstract="false" name="DebtSecuritiesAvailableforsaleFairValueMaturityAllocatedAndSingleMaturityDateAfterYearOneThroughTwo" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_DebtInstrumentLiborCap" abstract="false" name="DebtInstrumentLiborCap" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="bcrx_InterestExpenseAndRoyaltyFinancingObligationPolicyTextBlock" abstract="false" name="InterestExpenseAndRoyaltyFinancingObligationPolicyTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="bcrx_The2021RPIRoyaltyPurchaseAgreementMember" abstract="true" name="The2021RPIRoyaltyPurchaseAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_InducementPlanMember" abstract="true" name="InducementPlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_DescriptionOfCompanyPolicyTextBlock" abstract="false" name="DescriptionOfCompanyPolicyTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
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  <xs:element id="bcrx_RoyaltyPurchaseAgreementRoyaltiesAnnualNetSalesPaymentThreshold" abstract="false" name="RoyaltyPurchaseAgreementRoyaltiesAnnualNetSalesPaymentThreshold" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostExpectedToBeRecognizedYearFour" abstract="false" name="EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostExpectedToBeRecognizedYearFour" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
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  <xs:element id="bcrx_ShionogiCoLtdMember" abstract="true" name="ShionogiCoLtdMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_StockIssuedDuringPeriodValueWarrantsExercised" abstract="false" name="StockIssuedDuringPeriodValueWarrantsExercised" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_MilestoneRevenueMember" abstract="true" name="MilestoneRevenueMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_RoyaltyPurchaseAgreementRoyaltiesPercentageOfAnnualNetSalesInOtherMarkets" abstract="false" name="RoyaltyPurchaseAgreementRoyaltiesPercentageOfAnnualNetSalesInOtherMarkets" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="bcrx_RoyaltyPurchaseAgreementRoyaltiesPercentageOfPurchasePrice" abstract="false" name="RoyaltyPurchaseAgreementRoyaltiesPercentageOfPurchasePrice" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="bcrx_TermLoansABAndCDrawnMember" abstract="true" name="TermLoansABAndCDrawnMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_AnnualNetSalesBetween150000And230000Member" abstract="true" name="AnnualNetSalesBetween150000And230000Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_LaboratoryEquipmentOfficeEquipmentAndSoftwareMember" abstract="true" name="LaboratoryEquipmentOfficeEquipmentAndSoftwareMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostExpectedToBeRecognizedForRemainderOfFiscalYear" abstract="false" name="EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostExpectedToBeRecognizedForRemainderOfFiscalYear" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_AmortizationOfDiscountAndPremiumOnInvestments" abstract="false" name="AmortizationOfDiscountAndPremiumOnInvestments" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_SharesIssuedPricePerShareClosingPrice" abstract="false" name="SharesIssuedPricePerShareClosingPrice" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="bcrx_CollaborativeAgreementContractValue" abstract="false" name="CollaborativeAgreementContractValue" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_GreenCrossCorporationMember" abstract="true" name="GreenCrossCorporationMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_AvailableForSaleDebtSecuritiesAccruedInterest" abstract="false" name="AvailableForSaleDebtSecuritiesAccruedInterest" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
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  <xs:element id="bcrx_RenewablePeriodOfAgreement" abstract="false" name="RenewablePeriodOfAgreement" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="bcrx_LesseeOperatingLeaseAssetsAndLiabilitiesTableTextBlock" abstract="false" name="LesseeOperatingLeaseAssetsAndLiabilitiesTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="bcrx_AthyriumMember" abstract="true" name="AthyriumMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_RoyaltyMonetizationMember" abstract="true" name="RoyaltyMonetizationMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_MaximumCustomaryReductionOnRoyaltyRate" abstract="false" name="MaximumCustomaryReductionOnRoyaltyRate" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="bcrx_MaximumNumberOfProductsPermittedToBeObtainedDoses" abstract="false" name="MaximumNumberOfProductsPermittedToBeObtainedDoses" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="bcrx_SignificantAccountingPoliciesAndConcentrationsOfRiskLineItems" abstract="true" name="SignificantAccountingPoliciesAndConcentrationsOfRiskLineItems" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="bcrx_DebtInstrumentExitFeePercentageOfPrincipal" abstract="false" name="DebtInstrumentExitFeePercentageOfPrincipal" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="bcrx_AnnualNetSalesUnder15BillionMember" abstract="true" name="AnnualNetSalesUnder15BillionMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_RoyaltyPurchaseAgreementRoyaltiesPercentageOfSublicenseRevenueInOtherMarkets" abstract="false" name="RoyaltyPurchaseAgreementRoyaltiesPercentageOfSublicenseRevenueInOtherMarkets" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="bcrx_RoyaltyPurchaseAgreementRoyaltiesPercentageOfGlobalAnnualNetSales" abstract="false" name="RoyaltyPurchaseAgreementRoyaltiesPercentageOfGlobalAnnualNetSales" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="bcrx_StockIssuedDuringPeriodSharesWarrantsExercised" abstract="false" name="StockIssuedDuringPeriodSharesWarrantsExercised" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="bcrx_EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostExpectedToBeRecognizedYearTwo" abstract="false" name="EmployeeServiceShareBasedCompensationNonvestedAwardsCompensationCostExpectedToBeRecognizedYearTwo" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_TwentyTwentyRPIRoyaltyAgreementMember" abstract="true" name="TwentyTwentyRPIRoyaltyAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_AnnualNetSalesUnder150000Member" abstract="true" name="AnnualNetSalesUnder150000Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_MilestonePaymentMinimum" abstract="false" name="MilestonePaymentMinimum" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_AdditionalDevelopmentOptionsMember" abstract="true" name="AdditionalDevelopmentOptionsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_UABMember" abstract="true" name="UABMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_DebtInstrumentCommitmentFeePercentage" abstract="false" name="DebtInstrumentCommitmentFeePercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="bcrx_CollaborativeAndOtherResearchAndDevelopmentMember" abstract="true" name="CollaborativeAndOtherResearchAndDevelopmentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_CollaborativeAgreementContractCovenantMaximumAmountOfFunding" abstract="false" name="CollaborativeAgreementContractCovenantMaximumAmountOfFunding" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_ConcentrationOfMarketRiskPolicyTextBlock" abstract="false" name="ConcentrationOfMarketRiskPolicyTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="bcrx_AnnualNetSalesBetween350000And550000Member" abstract="true" name="AnnualNetSalesBetween350000And550000Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_EmployeeStockPurchasePlanMember" abstract="true" name="EmployeeStockPurchasePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_RoyaltyMonetizationTextBlock" abstract="false" name="RoyaltyMonetizationTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="bcrx_AccruedExpensesPolicyTextBlock" abstract="false" name="AccruedExpensesPolicyTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="bcrx_TwentyTwentyOneRPIRoyaltyAgreementMember" abstract="true" name="TwentyTwentyOneRPIRoyaltyAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_OMERSRoyaltyAgreementMember" abstract="true" name="OMERSRoyaltyAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_RoyaltyPurchaseAgreementRoyaltiesPercentageOfAnnualNetSales" abstract="false" name="RoyaltyPurchaseAgreementRoyaltiesPercentageOfAnnualNetSales" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="bcrx_TermLoansABAndCDrawnAndCureRightExercisedMember" abstract="true" name="TermLoansABAndCDrawnAndCureRightExercisedMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_NationalInstituteOfAllergyAndInfectiousDiseasesMember" abstract="true" name="NationalInstituteOfAllergyAndInfectiousDiseasesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_SeniorCreditFacilityMember" abstract="true" name="SeniorCreditFacilityMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_RoyaltyPurchaseAgreementRoyaltiesPurchasePriceAmount" abstract="false" name="RoyaltyPurchaseAgreementRoyaltiesPurchasePriceAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsPlanAmendmentAwardsInShares" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsPlanAmendmentAwardsInShares" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="bcrx_AnnualLicenseFeeMaximum" abstract="false" name="AnnualLicenseFeeMaximum" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_AmortizationOfDebtFinancingCostsAndOriginalIssueDiscounts" abstract="false" name="AmortizationOfDebtFinancingCostsAndOriginalIssueDiscounts" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_BCX9930BCX10013Member" abstract="true" name="BCX9930BCX10013Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_TermBAndCLoanMember" abstract="true" name="TermBAndCLoanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_DebtInstrumentPrepaymentFeePercentageOfPrincipalVoluntaryPayments" abstract="false" name="DebtInstrumentPrepaymentFeePercentageOfPrincipalVoluntaryPayments" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="bcrx_OperatingLeaseAssets" abstract="true" name="OperatingLeaseAssets" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="bcrx_RAPIVABMember" abstract="true" name="RAPIVABMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_ToriiPharmaceuticalCoMember" abstract="true" name="ToriiPharmaceuticalCoMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_PerformancebasedRestrictedStockUnitsMember" abstract="true" name="PerformancebasedRestrictedStockUnitsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_OtherSupplementalInformationRelatedToLeasesTableTextBlock" abstract="false" name="OtherSupplementalInformationRelatedToLeasesTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="bcrx_MidCapFinancialServicesLLCMember" abstract="true" name="MidCapFinancialServicesLLCMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_NumberOfProductsObtainedDoses" abstract="false" name="NumberOfProductsObtainedDoses" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="bcrx_InterestExpenseAndDeferredFinancingCostsPolicyTextBlock" abstract="false" name="InterestExpenseAndDeferredFinancingCostsPolicyTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="bcrx_RoyaltiesMonetizationsTable" abstract="true" name="RoyaltiesMonetizationsTable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType"/>
  <xs:element id="bcrx_PercentageOfCommonStockSharesEnding" abstract="false" name="PercentageOfCommonStockSharesEnding" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="bcrx_MaturityPeriodOfShortTermInvestment" abstract="false" name="MaturityPeriodOfShortTermInvestment" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="bcrx_RoyaltyPurchaseAgreementRoyaltiesPercentageOfAnnualNetSalesInKeyTerritories" abstract="false" name="RoyaltyPurchaseAgreementRoyaltiesPercentageOfAnnualNetSalesInKeyTerritories" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="bcrx_RoyaltyRateIfMaintainsSakigakeDesignation" abstract="false" name="RoyaltyRateIfMaintainsSakigakeDesignation" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="bcrx_USDepartmentOfHealthAndHumanServicesMember" abstract="true" name="USDepartmentOfHealthAndHumanServicesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_AnnualNetSalesOver3BillionsMember" abstract="true" name="AnnualNetSalesOver3BillionsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_PercentageOfSalaryToPurchaseCommonStockMaximum" abstract="false" name="PercentageOfSalaryToPurchaseCommonStockMaximum" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="bcrx_Vest25PercentEachYearUntilFullyVestedMember" abstract="true" name="Vest25PercentEachYearUntilFullyVestedMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_PikInterestPaymentIsMadeMember" abstract="true" name="PikInterestPaymentIsMadeMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_PriorToTheSecondAnniversaryMember" abstract="true" name="PriorToTheSecondAnniversaryMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_NonEmployeeDirectorsMember" abstract="true" name="NonEmployeeDirectorsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodAwardsAvailable" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodAwardsAvailable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="bcrx_AnnualLicenseFeeMinimum" abstract="false" name="AnnualLicenseFeeMinimum" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsForfeituresInPeriodAwardsAvailable" abstract="false" name="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsForfeituresInPeriodAwardsAvailable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="bcrx_RoyaltyReceivablesFromPartnersMember" abstract="true" name="RoyaltyReceivablesFromPartnersMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployeeAmount" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployeeAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_ShareBasedPaymentArrangementNumberOfPlans" abstract="false" name="ShareBasedPaymentArrangementNumberOfPlans" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="bcrx_DebtInstrumentCovenantMinimumUnrestrictedCashAndCashEquivalents" abstract="false" name="DebtInstrumentCovenantMinimumUnrestrictedCashAndCashEquivalents" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_PhaRMANotesMember" abstract="true" name="PhaRMANotesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_ProceedsFromAwardsForResearchAndDevelopmentContracts" abstract="false" name="ProceedsFromAwardsForResearchAndDevelopmentContracts" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_PrivatePlacementOfSeniorSecuredNotes" abstract="false" name="PrivatePlacementOfSeniorSecuredNotes" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_IncentivePlanMember" abstract="true" name="IncentivePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="bcrx_LesseeOperatingLeaseLiabilityToBePaidAfterYearFour" abstract="false" name="LesseeOperatingLeaseLiabilityToBePaidAfterYearFour" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="bcrx_ContractTerm" abstract="false" name="ContractTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="bcrx_DebtInstrumentPrepaymentFeePercentageOfAccruedInterest" abstract="false" name="DebtInstrumentPrepaymentFeePercentageOfAccruedInterest" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
</xs:schema>
