Viral Load

By the end of follow-up, negative Lassa virus RT-PCR was observed in 55% of favipiravir participants and 75% of ribavirin participants. Baseline RT-PCR cycle threshold values were similar between the favipiravir and ribavirin arms. PCR continues to detect residual RNA for weeks after a person has cleared live virus and is no longer infectious. Exploratory modeling suggested Ct values increased more slowly with favipiravir than with ribavirin. The viral kinetics result requires caution because participants had mild-to-moderate disease, high baseline Ct values, and poorly characterized symptom onset timing. RT-PCR may be an imperfect pharmacodynamic endpoint for favipiravir and ribavirin because detected RNA may not directly reflect viable virus clearance. The severity of infection is determined by the interaction between viral load and the strength of the individual's immune system. PCR begins detecting SARS-CoV-2 at around 1,000 particles per milliliter. People who are actively transmitting SARS-CoV-2 have viral loads of 1 million to 1 trillion particles per milliliter. SARS-CoV-2 viral particles in a nasal swab begin at approximately 10 particles per milliliter at the onset of in…