● Added South Korea to the planned study centers and clarified which European countries had been selected to participate ● Clarified PK sampling time points on Days 1, 3, and 5 ● Corrected the title of the Frailty Index to the Clinical Frailty Scale (CFS) ● Added an exclusion criterion for subjects requiring > 50% O2 when awake at screening ● Added an exclusion criteria for subjects scoring > 7 on the CFS at baseline ● Added RSV antibody titer blood draws at baseline and Day 14 ● Added viral-coinfection testing at baseline, and clarified that RSV and influenza sampling and testing at screening was to follow local laboratory procedures ● Clarified the exclusion criteria for chronic systemic immunosuppressive agents and the exclusion criteria related to pneumonia ● Deleted the exclusion criteria related to life-expectancy and to heart failure ● Removed the Clinical Symptom Score assessment and the European Quality of Life 5-Dimension utility measure (EQ5D-5L) questionnaire ● Modified the Flu-PRO secondary endpoint from AUC of change in score from baseline to Day 7 to daily average change in the Flu-PRO score from baseline to Day 5, and updated the Secondary Analysis sections accordingly ● Updated the Interim Analysis section to allow for an earlier assessment of futility and allow for study termination at a higher conditional power threshold ● Modified the primary endpoint from the AUC of log10 viral load from Day 1 to Day 7 to the daily average change in log10 viral load from Day 1 to Day 5, and updated the assumptions used in the sample size calculation ● Deleted the total number of intensive care unit (ICU) transfers exploratory endpoint

● Modification of contraceptive requirements ● Addition of phototoxicity text to the dosage and administration information ● Addition of text to address potential for drug-drug interactions (DDI) to the prior and concomitant medication information ● Addition of the EudraCT Number and the ClinicalTrials.gov Identifier ● Updated the terminology of relevant endpoints from daily averages to time-weighted averages as this term, along with difference between time-weighted average post-baseline and baseline (DAVG), is often used in literature. The definitions and calculations of the endpoints remained the same.

● Updated the list of countries in which study centers were planned ● Modified inclusion criteria to allow hospitalizations due to respiratory or non-respiratory reasons and to clarify that either upper or lower respiratory tract symptoms were acceptable, instead of requiring both ● Expanded exclusion criterion related to prednisone use to include similar corticosteroids ● Removed exclusion criteria related to history of bleeding disorder and to arrhythmia ● Replaced exclusion criterion for HIV/AIDS and hepatitis B or C status with a criterion excluding cluster determinant 4 (CD4) counts indicative of immunocompromised subjects ● Modified exclusion criterion related to bacteremia and fungemia ● Replaced exclusion criteria related to cerebrovascular accident or stroke, and admission for trauma or planned and emergent surgeries with a broader exclusion criterion to exclude subjects with unstable medical conditions ● Modified exclusionary laboratory values for relevance in the elderly patient population ● Clarified the 2-part consent process ● Clarified the use of admissions records to support enrollment and baseline data ● Added telephone visit as an option for Day 28 ● Administrative change to relocate collection of demographic information from baseline visit (Day 1) to screening (Day −1) in order to align with electronic data capture (EDC) requirements ● Administrative changes to Section 7.0 Adverse Events including rewording and reformatting for clarity ● Administrative change to update the sponsor address to the address of Gilead’s main headquarters ● Administrative change updating the primary medical monitor to Seth Toback, MD

● Added summary of the definitive embryo-fetal development study ● Added a section for ongoing clinical studies ● Completely revised the study design section for clarity ● Removed food-effect and phototoxicity wording from study drug dosing requirements ● Added End of Study and Post Study Care sections to the protocol ● Increased the number of study centers where the study was planned and added Hong Kong as a study location ● Clarified inclusion criterion for number of symptom days ● Added exclusion criterion for Middle East Respiratory Syndrome coronavirus (MERS-CoV) and other coronavirus coinfection ● Added moderate cytochrome P450 enzyme (CYP) inducers to the concomitant and prohibited medications ● Added recent historical evidence of pleural effusion and arterial blood pH to medical history requirements ● Added the option for home visits at Days 2, 3, 5, 7, and 14 ● Added Day 21 visit ● Updated Flu-PRO instructions ● Added the EQ5D-5L ● Standardized O2 saturation procedure across protocols ● Added Supplemental Oxygen Use Diary ● Added an ECG to Day 14 and updated ECG before dosing at baseline to a mandatory requirement ● Added requirement for collection of clinical data related to cardiac testing ● Added troponin blood draws before and after dosing at baseline and added an additional troponin blood draw at Day 14 ● Updated exploratory analyses based on the addition of the EQ5D-5L questionnaire. Analysis methods for other endpoints were also updated to include stratification factors in the model. ● Administrative change of all instances of GS-5806 to presatovir, excluding the study title ● Corrected typographical error in the EudraCT Number ● Administrative clarification that subjects could be discharged 30 minutes after dosing but were still required to complete all after dosing procedures ● Administrative addition of text regarding the Eligibility Criteria electronic case report form (eCRF) based off the new protocol template