● An optional extended viral monitoring section was created and appropriate text was included throughout the protocol to describe the study procedures during this period. In addition, planned analyses of the optional extended viral monitoring data were added to applicable sections of the protocol. ● The discontinuation criteria section was revised such that all Grade 3 or 4 adverse events (AEs) or serious adverse events (SAEs) must have been reviewed with the Gilead Sciences (Gilead) medical monitor to assess whether to continue study drug administration, to ensure that any Grade 3 or 4 AEs/SAEs that were associated with graft-versus-host disease (GVHD) or veno-occlusive disease were reviewed. ● Updated study drug instructions to recommend that subjects avoid direct UV exposure for the duration of exposure to presatovir (ie, 8 days following study drug administration), as the potential risk of phototoxicity was unknown and presatovir should have been almost completely eliminated within 8 days. ● The concomitant medications section was updated to address potential drug-drug interactions for presatovir and to clarify the need for safety monitoring consistent with the prescribing information for other agents when given concomitantly with presatovir, as presatovir affects transporters and has the potential to affect exposures of other drugs that depend on the same transporters. ● Appendix 5 was updated to provide additional information regarding pregnancy precautions and contraceptive requirements. ● The terminology of relevant endpoints was updated from daily averages to time-weighted averages as this term, along with time-weighted average change, is often used in literature. The definitions and calculations of the endpoints remained the same. ● Inclusion Criterion 2 was updated to < 48 hours prior to screening for clarity. ● Inclusion Criterion 7 was removed for consistency with Exclusion Criterion 3

● Exclusion Criterion 2 (washout period for strong cytochrome P450 enzyme [CYP] inducers) was extended from 1 to 2 weeks to reflect a more conservative washout period. ● Pregnancy testing was added at all dosing visits for females of childbearing potential for consistency with Appendix 5: Pregnancy Precautions, Definition for Female of Childbearing Potential, and Contraceptive Requirement. ● Male contraceptive and sperm donation requirements were extended from 30 to 90 days after last dose of study drug for consistency with the investigator’s brochure (IB). ● Inclusion Criterion 6 (contraceptive requirements) was modified in alignment with changes made to contraceptive requirements in Appendix 5.

● Removal of double-barrier method as contraceptive method to ensure all contraception is in accordance with the ICH M3 guidance that birth control methods need to be highly effective (ie, < 1% failure rate).

● Reproductive toxicology data in the protocol background was updated to reflect the definitive rat and rabbit studies. ● Exclusion Criterion 8 was removed as the intent of the criterion is covered in Exclusion Criterion 13 ● Exclusion Criteria 16 and 17 (aspartate aminotransferase [AST]/alanine aminotransferase [ALT] and total bilirubin [TBIL] requirements), discontinuation criteria, and safety labs were updated to include hepatic monitoring consistent with Canadian regulations. ● Study drug administration information updated to allow for nasogastric (NG) tube administration, and removal of the need for fasting or avoidance of direct UV exposure per new stability and phototoxicity data of GS-5806-02. ● Study drug discontinuation criteria updated to include extra hepatic monitoring and Hy’s law in accordance with Canadian regulations. ● Secondary and exploratory endpoints and analyses updated ● Induced sputum removed as collection of this sample is not standard practice. ● Section 1.2.2 was updated for consistency with the IB. ● A new Inclusion Criterion 1 was added to clarify age ranges allowed in the study. ● Exclusion Criterion 2 (CYP restrictions) and Section 5.4: Prior and Concomitant Medications were updated to further exclude moderate CYP inducers, as DDI results indicated that moderate CYP inducers moderately decrease presatovir exposure. ● Exclusion Criterion 8 (other respiratory viruses) was updated to exclude coronaviruses due to severe clinical disease now known to be associated with Middle East respiratory syndrome. ●Exclusion Criterion 14 (allergy to sulfa drugs) was updated to clarify that the criterion applies to sulfa reactions that are of most concern. ● Hepatic monitoring and statistical texts were updated for clarity

● Section 1.2.4.4: Ongoing Studies was added to provide consistency among protocols in the presatovir program. ● Inclusion Criteria 4 (documented RSV) and Section 6.11.1: Nasal Samples, Virology, and Antibody Titer were updated to clarify that spontaneous sputum is not allowed. ● Screening RSV testing was updated to allow for standard clinical practice procedures surrounding RSV diagnosis confirmation and in meeting study inclusion criteria. ● Electrocardiograms (ECGs), troponin testing, and collection of standard of care clinical data for central review were added. ● The prior and concomitant medications section was updated to attribute part of cyclosporine effect as a weak CYP3A inhibitor, to clarify that presatovir is not expected to alter PK of concomitant medications that are substrates of major CYP enzymes or drug transporters, and to note that the potential effect of strong- and moderate-CYP3A inhibitors on presatovir PK are under investigation. ● Vital signs and O2 saturation measurement were added to Visits 3 and 5, if not home visits, and study-specific assessments were added to all study visits for consistency. ● The O2 saturation measurement procedure was updated for consistency across the presatovir program and to allow subjects to remain on chronic O2 for standards in clinical care.

● Screening procedures were modified such that subjects who were not tested for RSV as standard of care could consent to the study and be tested for RSV during the screening visit. ● Visit 3 was made optional if the subject was not hospitalized at the time of visit to reduce the visit burden during the first 9 days of the study. ● The number of sites was increased in order to accelerate enrollment. ● Sweden-specific requirements for obtaining consent via legal guardian were added to the inclusion criteria. ● Section 6.1.1: Visit 1: Screening Visit was updated to allow subjects who screen failed out of GS-US-218-0108 due to presence of LRTI to screen into GS-US-218-1502 and vice versa. ● Administrative clarifications were made to Section 8: Statistical Considerations.