for people ages 18-69 (full criteria)
at San Francisco, California
study started
completion around
Principal Investigator
by Timothy Henrich, MDMichael Peluso, MD
Headshot of Timothy Henrich
Timothy Henrich
Headshot of Michael Peluso
Michael Peluso



Persistent viral infection with viral reservoirs and detection of circulating spike protein after the initial acute illness is one potential pathogenic mechanism for Long COVID. This mechanism may be susceptible to antiviral therapy that blocks viral replication, which has the potential to alleviate long COVID symptoms. This trial will study the safety and efficacy of Ensitrelvir (S-217622), an antiviral, to treat individuals with Long COVID in an adult population.

Official Title

Placebo-Controlled, Randomized Trial of Ensitrelvir (S-217622) for Viral Persistence and Inflammation in People Experiencing Long COVID (PREVAIL-LC)


The study will enroll approximately 40 participants who meet the World Health Organization (WHO) Long COVID criteria. Participants will be enrolled at a single center and randomized 1:1 to receive ensitrelvir fumaric acid (Ensitrelvir: S-217622), given orally for 5 days, or placebo. Subjects randomized to receive Ensitrelvir will take 375 mg on day 1, followed by 125 mg daily for 4 additional days. Evaluations will take place at baseline and at timepoints up to 60 days post-initiation of study drug.


Long COVID, Post Acute Sequelae of COVID-19, Post-Acute COVID-19, Antiviral, Viral Persistence, COVID-19, Post-Acute COVID-19 Syndrome, Inflammation, Ensitrelvir, Ensitrelvir (S-217622)


You can join if…

Open to people ages 18-69

(note, additional eligibility criteria not listed here will be assessed at Screening):

- ≥18 and <70 years of age at Screening. - History of confirmed SARS-CoV-2 infection. - Long COVID attributed to a SARS-CoV-2 infection - At least two moderate symptoms or one severe symptom that are new or worsened since the time of a SARS-CoV-2 infection, not known to be attributable to another cause upon assessment by the PI. Symptoms must have been present for at least 60 days prior to screening and must be reported to be at least somewhat bothersome. - Body mass index (BMI) 18 to 50 kilograms/meter squared (kg/m2), inclusive, at the time of screening. - Participants who are of childbearing potential (CBP) and male participants with sexual partner(s) who are females of CBP must agree to use adequate contraception from study consent through 14 days after the last dose of study intervention.

You CAN'T join if...

(note, additional eligibility criteria not listed here will be assessed at Screening):

- Previously received SARS-CoV-2 antiviral within 90 days prior to planned Day 0 or plan to receive such treatment before exiting the study - Previously received COVID-19 convalescent plasma treatment within 60 days prior to planned Day 0 or plan to receive such treatment before exiting the study. - Plans to receive any investigational or approved vaccine or booster for SARS-CoV-2 within 60 days prior to Day 0 or before Day 30 following Day 0. - Active cardiovascular disease or recent (within 3 months) stroke. - Recent (within 6 months) or planned major surgery. - Currently hospitalized or recent (within 1 month) unplanned hospitalization. - Active Hepatitis B or C infection. - Known HIV infection. - Severe coagulopathy (international normalized ratio ((INR) >2.0, history of hemophilia). - Severe anemia (hemoglobin <9 grams/deciliter (g/dL)). - Moderate or severe immunocompromise, according to the current NIH COVID-19 Treatment Guidelines as of March 6, 2023. - History of anaphylaxis or hypersensitivity to any components of the intervention, prescription or non-prescription drugs, or food products in the past. - Known prior diagnosis of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), preceding and not related to SARS-CoV-2 infection and not worsened since SARS-CoV-2 infection - Pregnant, breastfeeding, or unwilling to practice birth control abide by the contraception requirements outlined in the inclusion criteria. - Participation in a clinical trial with receipt of an investigational product within 28 days prior to Day 0. - Presence of a condition or abnormality that in the opinion of the Investigator would compromise the safety of the patient or the quality of the data.


  • UCSF/Zuckerberg San Francisco General Hospital accepting new patients
    San Francisco California 94110 United States

Lead Scientists at UCSF

  • Timothy Henrich, MD
    My laboratory/research group specializes in immunmodulatory, cytoreductive chemotherapeutic and stem cell transplantation approaches to HIV-1 cure. We are also involved in the design and implementation of novel nano/microtechnologies and PET-based imaging approaches to characterize viral reservoirs.
  • Michael Peluso, MD
    I am an infectious disease clinical-translational physician-scientist. My primary interests are HIV and COVID-19. I am involved with clinical and laboratory research aimed at understanding the HIV reservoir and implementing clinical trials to disrupt the reservoir with the aim of inducing antiretroviral therapy-free HIV remission.


accepting new patients
Start Date
Completion Date
Timothy Henrich
Phase 2 COVID-19 Research Study
Study Type
Expecting 40 study participants
Last Updated