Tixagevimab-cilgavimab (AZD7442) for the treatment of patients hospitalized with COVID-19 (DisCoVeRy): A phase 3, randomized, double-blind, placebo-controlled trial (preprint)

Background Tixagevimab and cilgavimab (AZD7442) are two monoclonal antibodies developed by AstraZeneca for the pre-exposure prophylaxis and treatment of patients infected by SARS-CoV-2. Its effectiveness and safety in patients hospitalized with COVID-19 was not known at the outset of this trial. Methods DisCoVeRy is a phase 3, adaptive, multicentre, randomized, controlled trial conducted in 63 sites in Europe. Participants were randomly assigned (1:1) to receive placebo or tixagevimab-cilgavimab in addition to standard of care. The primary outcome was the clinical status at day 15 measured by the WHO seven-point ordinal scale. Several clinical, virological, immunological and safety endpoints were also assessed. Findings Due to slow enrolment, recruitment was stopped on July 1st, 2022. The antigen positive modified intention-to-treat population (mITT) was composed of 173 participants randomized to tixagevimab-cilgavimab (n=91) or placebo (n=82), 91.9% (159/173) with supplementary oxygen, and 47.4% (82/173) previously vaccinated at inclusion. There was no significant difference in the distribution of the WHO ordinal scale at day 15 between the two groups (odds ratio (OR) 0.93, 95%CI [0.54-1.61]; p=0.81) nor in any clinical, virological or safety secondary endpoints. In the global mITT (n=226), neutralization antibody titers were significantly higher in the tixagevimab-cilgavimab group/patients compared to placebo at day 3 (Least-square mean differences (LSMD) 1.44, 95% Confidence interval (CI) [1.20-1.68]; p < 10-23) and day 8 (LSMD 0.91, 95%CI [0.64-1.18]; p < 10-8) and it was most important for patients infected with a pre-omicron variant, both at day 3 (LSMD 1.94, 95% CI [1.67-2.20], p < 10-25) and day 8 (LSMD 1.17, 95% CI [0.87-1.47], p < 10-9), with a significant interaction (p < 10-7 and p=0.01 at days 3 and 8, respectively). Interpretation There were no significant differences between tixagevimab-cilgavimab and placebo in clinical endpoints, however the trial lacked power compared to prespecified calculations. Tixagevimab-cilgavimab was well tolerated, with low rates of treatment related events.

Modelling the association between neutralizing antibody levels and SARS-CoV-2 viral dynamics : implications to define correlates of protection against infection (preprint)

Background While anti-SARS-CoV-2 antibody kinetics have been well described in large populations of vaccinated individuals, we still poorly understand how they evolve during a natural infection and how this impacts viral clearance. Methods For that purpose, we analyzed the kinetics of both viral load and neutralizing antibody levels in a prospective cohort of individuals during acute infection by Alpha variant. Results Using a mathematical model, we show that the progressive increase in neutralizing antibodies leads to a shortening of the half-life of both infected cells and infectious viral particles. We estimated that the neutralizing activity reached 90% of its maximal level within 8 days after symptoms onset and could reduce the half-life of both infected cells and infectious virus by a 6-fold factor, thus playing a key role to achieve rapid viral clearance. Using this model, we conducted a simulation study to predict in a more general context the protection conferred by the existence of pre-existing neutralization, due to either vaccination or prior infection. We predicted that a neutralizing activity, as measured by ED50 >103, could reduce by 50% the risk of having viral load detectable by standard PCR assays and by 99% the risk of having viral load above the threshold of cultivable virus. Conclusions This threshold value for the neutralizing activity could be used to identify individuals with poor protection against disease acquisition.

Impact of variants of concern on SARS-CoV-2 viral dynamics in non-human primates. (preprint)

The impact of variants of concern (VoC) on SARS-CoV-2 viral dynamics remains poorly understood and essentially relies on observational studies subject to various sorts of biases. In contrast, experimental models of infection constitute a powerful model to perform controlled comparisons of the viral dynamics observed with VoC and better quantify how VoC escape from the immune response. Here we used molecular and infectious viral load of 78 cynomolgus macaques to characterize in detail the effects of VoC on viral dynamics. We first developed a mathematical model that recapitulate the observed dynamics, and we found that the best model describing the data assumed a rapid antigen-dependent stimulation of the immune response leading to a rapid reduction of viral infectivity. When compared with the historical variant, all VoC except beta were associated with an escape from this immune response, and this effect was particularly sensitive for delta and omicron variant (p<10-6 for both). Interestingly, delta variant was associated with a 1.8-fold increased viral production rate (p=0.046), while conversely omicron variant was associated with a 14-fold reduction in viral production rate (p<10-6). During a natural infection, our models predict that delta variant is associated with a higher peak viral RNA than omicron variant (7.6 log10 copies/mL 95% CI 6.8 - 8 for delta; 5.6 log10 copies/mL 95% CI 4.8 - 6.3 for omicron) while having similar peak infectious titers (3.7 log10 PFU/mL 95% CI 2.4 - 4.6 for delta; 2.8 log10 PFU/mL 95% CI 1.9 - 3.8 for omicron). These results provide a detailed picture of the effects of VoC on total and infectious viral load and may help understand some differences observed in the patterns of viral transmission of these viruses.

Remdesivir for the treatment of hospitalised patients with COVID-19: final results from the DisCoVeRy randomised, controlled, open-label trial (preprint)

Background: The antiviral efficacy of remdesivir is still controversial. We aimed at evaluating its clinical effectiveness in hospitalised patients with COVID-19, with indication of oxygen and/or ventilator support. Following prior publication of preliminary results, here we present the final results after completion of data monitoring. Methods: In this European multicentre, open-label, parallel-group, randomised, controlled trial (DisCoVeRy, NCT04315948, EudraCT2020-000936-23), participants were randomly allocated to receive usual standard of care (SoC) alone or in combination with remdesivir, lopinavir/ritonavir, lopinavir/ritonavir and IFN-beta-1a, or hydroxychloroquine. Adult patients hospitalised with COVID-19 were eligible if they had clinical evidence of hypoxemic pneumonia, or required oxygen supplementation. Exclusion criteria included elevated liver enzyme, severe chronic kidney disease, any contra-indication to one of the studied treatments or their use in the 29 days before randomization, or use of ribavirin, as well as pregnancy or breast-feeding. Here, we report results for remdesivir + SoC versus SoC alone. Remdesivir was administered as 200 mg infusion on day 1, followed by once daily infusions of 100 mg up to 9 days, for a total duration of 10 days. It could be stopped after 5 days if the participant was discharged. Treatment assignation was performed via web-based block randomisation stratified on illness severity and administrative European region. The primary outcome was the clinical status at day 15 measured by the WHO 7-point ordinal scale, assessed in the intention-to-treat population. Findings: Between March 22nd, 2020 and January 21st, 2021, 857 participants were randomised to one of the two arms in 5 European countries and 843 participants were included for the evaluation of remdesivir (control, n=423; remdesivir, n=420). At day 15, the distribution of the WHO ordinal scale was as follow in the remdesivir and control groups, respectively: Not hospitalized, no limitations on activities: 62/420 (14.8%) and 72/423 (17.0%); Not hospitalized, limitation on activities: 126/420 (30%) and 135/423 (31.9%); Hospitalized, not requiring supplemental oxygen: 56/420 (13.3%) and 31/423 (7.3%); Hospitalized, requiring supplemental oxygen: 75/420 (17.9%) and 65/423 (15.4%); Hospitalized, on non-invasive ventilation or high flow oxygen devices: 16/420 (3.8%) and 16/423 (3.8%); Hospitalized, on invasive mechanical ventilation or ECMO: 64/420 (15.2%) and 80/423 (18.9%); Death: 21/420 (5%) and 24/423 (5.7%). The difference between treatment groups was not statistically significant (OR for remdesivir, 1.02, 95% CI, 0.62 to 1.70, P=0.93). There was no significant difference in the occurrence of Serious Adverse Events between treatment groups (remdesivir, n=147/410, 35.9%, versus control, n=138/423, 32.6%, p=0.29). Interpretation: Remdesivir use for the treatment of hospitalised patients with COVID-19 was not associated with clinical improvement at day 15. Funding: European Union Commission, French Ministry of Health, DIM One Health Ile-de-France, REACTing, Fonds Erasme-COVID-ULB; Belgian Health Care Knowledge Centre (KCE), AGMT gGmbH, FEDER "European Regional Development Fund", Portugal Ministry of Health, Portugal Agency for Clinical Research and Biomedical Innovation. Remdesivir was provided free of charge by Gilead.

Activity of Tixagevimab/Cilgavimab against the Omicron variant of SARS-CoV-2 in a hamster model (preprint)

The efficacy of pre-exposure prophylaxis by the Tixagevimab/Cilgavimab cocktail (AZD7442) was evaluated in hamsters against a clinical BA.1 strain of SARS-CoV-2 variant Omicron. AZD7442 retains inhibitory activity against Omicron despite a substantial loss of efficacy. We estimate that Omicron virus requires about 20-times more antibodies in plasma than the ancestral B.1 strain (G614) virus to achieve a similar drug efficacy in reducing lung infectious titers.

Modeling brings additional insights into the kinetics of SARS-CoV-2 neutralizing antibody (preprint)

Following the paper by Seow et al. published in Nature Microbiology, we reanalyzed the publicly available data using dynamical models of humoral response. The main conclusion is that, from available data, we can demonstrate that the decline of neutralizing antibodies (as measured with ID50) is biphasic, which is compatible with two types of antibody secreting cells (short lived and long lived). We found that lower bound of half life of the long-lived antibody secreting cells is 450 days. Moreover, our model predicts that the neutralizing antibody response could be more durable than suggested (up to 129 days for individuals with no requirement of supplemental oxygen and up to 175 days for others). A result which adds insight on the longevity of immune response.

Modeling remdesivir antiviral efficacy in COVID-19 hospitalized patients of the randomized, controlled, open-label DisCoVeRy trial (preprint)

Despite several clinical studies, the antiviral efficacy of remdesivir in COVID-19 hospitalized patients remains controversial. We analyzed nasopharyngeal normalized viral loads collected in the 29 days following randomization from 665 hospitalized patients included in the DisCoVeRy trial, allocated to either standard of care (SoC, N=329) or SoC + remdesivir for 10 days (N=336). We used a mathematical model to reconstruct viral kinetic profiles and estimate the antiviral efficacy of remdesivir in reducing viral production. To identify factors associated with viral kinetics, additional analyses were conducted stratified either on time of treatment initiation ([≤] or > 7 days since symptom onset) or viral load at randomization (< or [≥] 3.5 log10 copies/104 cells). In our model, remdesivir reduced viral production by 2-fold on average (95%CI: 1.5-3.2). Using the estimated parameter of the model, simulations predict that remdesivir reduces time to viral clearance by 0.7 day compared to SoC, with large inter-individual variabilities (Inter-Quartile Range, IQR: 0.0-1.3 days). Exploratory analyses suggest that remdesivir had a larger impact in patients with a high viral load at randomization, reducing viral production by 5-fold on average (95%CI: 2.8-25), leading to a predicted median reduction in the time to viral clearance of 2.4 days (IQR: 0.9-4.5 days). In summary, our model shows that remdesivir reduces viral production from infected cells by a factor 2, leading to a median reduction of 0.7 days in the time to viral clearance compared to SoC. The efficacy was larger in patients with high level of viral load at treatment initiation. One sentence summaryRemdesivir reduces the time to SARS-CoV-2 clearance by 1 day in hospitalized patients, and up to 3 days in those with high viral load at admission.

Variant-specific SARS-CoV-2 within-host kinetics (preprint)

Since early 2021, SARS-CoV-2 variants of concern (VOCs) have been causing epidemic rebounds in many countries. Their properties are well characterised at the epidemiological level but the potential underlying within-host determinants remain poorly understood. We analyse a longitudinal cohort of 6,944 individuals with 14,304 cycle threshold (Ct) values of qPCR VOC screening tests performed in the general population and hospitals in France between February 6 and August 21, 2021. To convert Ct values into numbers of virus copies, we performed an additional analysis using droplet digital PCR (ddPCR). We find that the number of viral genome copies reaches a higher peak value and has a slower decay rate in infections caused by Alpha variant compared to that caused by historical lineages. Following the evidence that viral genome copies in upper respiratory tract swabs are informative on contagiousness, we show that the kinetics of the Alpha variant translate into significantly higher transmission potentials, especially in older populations. Finally, comparing infections caused by the Alpha and Delta variants, we find no significant difference in the peak viral copy number. These results highlight that some of the differences between variants may be detected in virus load variations.

Remdesivir for the Treatment of Hospitalised Patients with COVID-19 (DisCoVeRy): A Randomised, Controlled, Open-Label Trial (preprint)

Background: The antiviral efficacy of remdesivir is still controversial. We aimed at evaluating its clinical effectiveness in patients with COVID-19 requiring oxygen and/or ventilator support.Methods: In this European multicentre, open-label, parallel-group, randomised, controlled trial in adults hospitalised with COVID-19 (DisCoVeRy, NCT04315948; EudraCT2020-000936-23), participants were randomly allocated to receive usual standard of care alone or in combination with intravenous remdesivir (200 mg on day 1, then 100 mg once-daily for 9 days or until discharge). Treatment assignation was performed via web-based randomisation stratified on illness severity and administrative European region. The primary outcome was the clinical status at day 15 measured by the WHO 7-point ordinal scale, assessed in the intention-to-treat population.Findings: Between March 22nd, 2020 and January 21st, 2021, 857 participants were randomised to one of the two arms in 5 European countries and 832 participants were included for the evaluation of remdesivir (control, n=418; remdesivir, n=414). There was no difference in the clinical status neither at day 15 between treatment groups (OR for remdesivir, 0.98, 95% CI, 0.77 to 1.25, P=0.85) nor at day 29. The proportion of deaths at day 28 was not significantly different between control (8.9%) and remdesivir (8.2%) treatment groups (OR for remdesivir, 0.93 95%CI 0.57 to 1.52, P=0.77). There was also no difference on SARS-CoV-2 viral kinetics (effect of remdesivir on viral load slope, -0.004 log10 cp/10,000 cells/day, 95% CI, -0.03 to 0.02, P=0.75). There was no significant difference in the occurrence of Serious Adverse Events between treatment groups.Interpretation: The use of remdesivir for the treatment of hospitalised patients with COVID-19 was not associated with clinical improvement at day 15 or day 29, nor with a reduction in mortality, nor with a reduction in SARS-CoV-2 RNA.Trial Registration: DisCoVeRy, NCT04315948; EudraCT2020-000936-23Funding: European Union Commission, French Ministry of Health, DIM One Health Île-de-France, REACTing, Fonds Erasme-COVID-ULB; Belgian Health Care Knowledge Centre (KCE)Declaration of Interests: Dr. Costagliola reports grants and personal fees from Janssen, personal fees from Gilead, outside the submitted work. Dr. Mentré reports grants from INSERM Reacting (French Government), grants from Ministry of Health (French Government), grants from European Commission, during the conduct of the study; grants from Sanofi, grants from Roche, outside the submitted work. Dr. Hites reports grants from The Belgian Center for Knowledge (KCE), grants from Fonds Erasme-COVID-ULB, during the conduct of the study; personal fees from Gilead, outside the submitted work. Dr. Mootien reports non-financial support from GILEAD, outside the submitted work. Dr. Gaborit reports non-financial support from Gilead, non- financial support from MSD, outside the submitted work. Dr. Botelho-Nevers reports other from Pfizer, other from Janssen, outside the submitted work. Dr. Lacombe reports personal fees and non-financial support from Gilead, personal fees and non-financial support from Janssen, personal fees and non-financial support from MSD, personal fees and non-financial support from ViiV Healthcare, personal fees and non-financial support from Abbvie, during the conduct of the study. Dr. Wallet reports personal fees and non-financial support from Jazz pharmaceuticals, personal fees and non-financial support from Novartis, personal fees and nonPage financial support from Kite-Gilead, outside the submitted work. Dr. Kimmoun reports personal fees from Aguettan, personal fees from Aspen, outside the submitted work. Dr. Thiery reports personal fees from AMGEN, outside the submitted work. Dr. Burdet reports personal fees from Da Volterra, personal fees from Mylan Pharmaceuticals, outside the submitted work. Dr. Poissy reports personal fees from Gilead for lectures, outside the submitted work. Dr. Goehringer reports personal fees from Gilead Sciences, non-financial support from Gilead Sciences, grants from Biomerieux, non-financial support from Pfizer, outside the submitted work. Dr. Peytavin reports personal fees from Gilead Sciences, personal fees from Merck France, personal fees from ViiV Healthcare, personal fees from TheraTechnologies, outside the submitted work. Dr. Danion reports personal fees from Gilead, outside the submitted work. Dr. Raffi reports personal fees from Gilead, personal fees from Janssen, personal fees from MSD, personal fees from Abbvie, personal fees from ViiV Healthcare, personal fees from Theratechnologies, personal fees from Pfizer, outside the submitted work. Dr. Gallien reports personal fees from Gilead, personal fees from Pfizer, personal fees from ViiV, personal fees from MSD, outside the submitted work; and has received consulting fee from Gilead in August 2020 to check the registration file of remdesivir for the French administration. Dr. Nseir reports personal fees from MSD, personal fees from Pfizer, personal fees from Gilead, personal fees from Biomérieux, personal fees from BioRad, outside the submitted work. Dr. Lefèvre reports personal fees from Mylan, personal fees from Gilead, outside the submitted work. Dr. Guedj reports personal fees from Roche, outside the submitted work. Other authors have nothing to disclose.Ethics Approval Statement: The trial was approved by the Ethics Committee (CPP Ile-de-France-III, approval #20.03.06.51744), and is sponsored by the Institut national de la santé et de la recherche médicale (Inserm, France); it was conducted in accordance with the Declaration of Helsinki. Written informed consent was obtained from all included participants (or their legal representatives if unable to consent). The present analysis is based on the protocol v11.0 of December 12th, 2020.

Quantifying the relationship between SARS-CoV-2 viral load and infectiousness. (preprint)

The relationship between SARS-CoV-2 viral load and infectiousness is not known. Using data from a prospective cohort of index cases and high-risk contact, we reconstructed by modelling the viral load at the time of contact and the probability of infection. The effect of viral load was particularly large in household contacts, with a transmission probability that increased to as much as 37% when the viral load was greater than 10 log 10 copies per mL. The transmission probability peaked at symptom onset in most individuals, with a median probability of transmission of 15%, that hindered large individual variations (IQR: [8, 37]). The model also projects the effects of variants on disease transmission. Based on the current knowledge that viral load is increased by 2 to 4-fold on average, we estimate that infection with B1.1.7 virus could lead to an increase in the probability of transmission by 8 to 17%.

COVA1-18 neutralizing antibody protects against SARS-CoV-2 in three preclinical models (preprint)

One year into the Coronavirus Disease 2019 (COVID-19) pandemic caused by Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2), effective treatments are still needed1–3. Monoclonal antibodies, given alone or as part of a therapeutic cocktail, have shown promising results in patients, raising the hope that they could play an important role in preventing clinical deterioration in severely ill or in exposed, high risk individuals4–6. Here, we evaluated the prophylactic and therapeutic effect of COVA1-18 in vivo, a neutralizing antibody isolated from a convalescent patient7 and highly potent against the B.1.1.7. isolate8,9. In both prophylactic and therapeutic settings, SARS-CoV-2 remained undetectable in the lungs of COVA1-18 treated hACE2 mice. Therapeutic treatment also caused a dramatic reduction in viral loads in the lungs of Syrian hamsters. When administered at 10 mg kg− 1 one day prior to a high dose SARS-CoV-2 challenge in cynomolgus macaques, COVA1-18 had a very strong antiviral activity in the upper respiratory compartments with an estimated reduction in viral infectivity of more than 95%, and prevented lymphopenia and extensive lung lesions. Modelling and experimental findings demonstrate that COVA1-18 has a strong antiviral activity in three different preclinical models and could be a valuable candidate for further clinical evaluation.

High-risk exposure without personal protective equipment and infection with SARS-CoV-2 in healthcare workers: results of the CoV-CONTACT prospective cohort (preprint)

Objective: We aimed to estimate the risk of infection in Healthcare workers (HCWs) following a high-risk exposure without personal protective equipment (PPE). Methods: We conducted a prospective cohort in HCWs who had a high-risk exposure to SARS-CoV-2-infected subject without PPE. Daily symptoms were self-reported for 30 days, nasopharyngeal swabs for SARS-CoV-2 RT-PCR were performed at inclusion and at days 3, 5, 7 and 12, SARS-CoV-2 serology was assessed at inclusion and at day 30. Confirmed infection was defined by positive RT-PCR or seroconversion, and possible infection by one general and one specific symptom for two consecutive days. Results: Between February 5th and May 30th, 2020, 154 HCWs were enrolled within 14 days following one high-risk exposure to either a hospital patient (70/154; 46.1%) and/or a colleague (95/154; 62.5%). At day 30, 25.0% had a confirmed infection (37/148; 95%CI, 18.4%; 32.9%), and 43.9% (65/148; 95%CI, 35.9%; 52.3%) had a confirmed or possible infection. Factors independently associated with confirmed or possible SARS-CoV-2 infection were being a pharmacist or administrative assistant rather than being from medical staff (adjusted OR (aOR)=3.8, CI95%=1.3;11.2, p=0.01), and exposure to a SARS-CoV-2-infected patient rather than exposure to a SARS-CoV-2-infected colleague (aOR=2.6, CI95%=1.2;5.9, p=0.02). Among the 26 HCWs with a SARS-CoV-2-positive nasopharyngeal swab, 7 (26.9%) had no symptom at the time of the RT-PCR positivity. Conclusions: The proportion of HCWs with confirmed or possible SARS-CoV-2 infection was high. There were less occurrences of high-risk exposure with patients than with colleagues, but those were associated with an increased risk of infection.

Viral dynamic modeling of SARS-CoV-2 in non-human primates (preprint)

Non-human primates infected with SARS-CoV-2 exhibit mild clinical signs. Here we used a mathematical model to characterize in detail the viral dynamics in 31 cynomolgus macaques infected with 106 pfu of SARS-CoV-2 for which nasopharyngeal and tracheal viral load were frequently assessed. We identified that infected cells had a large daily viral production (>104 virus) and a within-host reproductive basic number of 6 and 4 in nasopharyngeal and tracheal compartment, respectively. After peak viral load, infected cells were rapidly cleared with a half-life of 9 hours, with no significant association between cytokine elevation and clearance. Translating our model to the context of human-to-human infection, human mild infection may be characterized by a peak occurring 4 days after infection, a viral shedding of ~11 days and a generation time of 4 days. These results improve the understanding of SARS-CoV-2 viral replication and better understand the infection to SARS-CoV-2 in humans.

Favipiravir and severe acute respiratory syndrome coronavirus 2 in hamster model (preprint)

Despite no or limited pre-clinical evidence, repurposed drugs are massively evaluated in clinical trials to palliate the lack of antiviral molecules against SARS-CoV-2. Here we used a Syrian hamster model to assess the antiviral efficacy of favipiravir, understand its mechanism of action and determine its pharmacokinetics. When treatment was initiated before or simultaneously to infection, favipiravir had a strong dose effect, leading to dramatic reduction of infectious titers in lungs and clinical alleviation of the disease. Antiviral effect of favipiravir correlated with incorporation of a large number of mutations into viral genomes and decrease of viral infectivity. The antiviral efficacy observed in this study was achieved with plasma drug exposure comparable with those previously found during human clinical trials and was associated with weight losses in animals. Thereby, pharmacokinetic and tolerance studies are required to determine whether similar effects can be safely achieved in humans.

Repurposed prophylaxis strategies for COVID-19: a systematic review (preprint)

Introduction Efficient therapeutic strategies are needed to counter the COVID-19 pandemic, caused by the SARS- CoV-2 virus. In a context where specific vaccines are not yet available, the containment of the pandemic would be facilitated with efficient prophylaxis. Methods We screened several clinical trials repositories and platforms in search of the prophylactic strategies that are investigated against COVID-19 in late April 2020. Results Up to April 27, 2020, we found 68 clinical trials targeting medical workers (n=43, 63%), patients relatives (n=16, 24%) or individuals at risk of severe COVID-19 (n=5, 7%). (Hydroxy)chloroquine was the most frequently evaluated treatment (n=46, 68%), before BCG vaccine (n=5, 7%). Sixty-one (90%) clinical trials were randomized with a median of planned inclusions of 600 (IQR 255-1515). Conclusion The investigated prophylaxis strategies cover both pre- and post-exposure prophylaxis and study numerous immune enhancers and antivirals, although most research efforts are focused on (hydroxy)chloroquine.

Predicted success of prophylactic antiviral therapy to block or delay SARS-CoV-2 infection depends on the targeted mechanism (preprint)

Repurposed drugs that are immediately available and safe to use constitute a first line of defense against new viral infections. Despite limited antiviral activity against SARS-CoV-2, several drugs are being tested as medication or as prophylaxis to prevent infection. Using a stochastic model of early phase infection, we find that a critical efficacy above 87% is needed to block viral establishment. This can be improved by combination therapy. Below the critical efficacy, establishment of infection can sometimes be prevented, most effectively with drugs blocking viral entry into cells or enhancing viral clearance. Even when a viral infection cannot be prevented, antivirals delay the time to detectable viral loads. This delay flattens the within-host viral dynamic curve, possibly reducing transmission and symptom severity. Thus, antiviral prophylaxis, even with reduced efficacy, could be efficiently used to prevent or alleviate infection in people at high risk.

Hydroxychloroquine in the treatment and prophylaxis of SARS-CoV-2 infection in non-human primates (preprint)

COVID-19 has become a pandemic that has caused over 200,000 deaths worldwide, with no antiviral drug or vaccine yet available. Several clinical studies are ongoing to evaluate the efficacy of repurposed drugs that have demonstrated antiviral efficacy in vitro. Among these candidates, hydroxychloroquine (HCQ) has been given to thousands of individuals worldwide but definitive evidence for HCQ efficacy in treatment of COVID-19 is still missing.We evaluated the antiviral activity of HCQ both in vitro and in SARS-CoV-2-infected macaques. HCQ showed antiviral activity in monkey African green monkey kidney (VeroE6) cells but not in a model of reconstituted human airway epithelium. In macaques, we tested different treatment strategies in comparison to placebo, before and after peak viral load, alone or in combination with azithromycin (AZTH). Neither HCQ nor HCQ+AZTH showed a significant effect on the viral load levels in any of the tested compartments. When the drug was used as a pre-exposure prophylaxis (PrEP), HCQ did not confer protection against acquisition of infection.Our findings do not support the use of HCQ, either alone or in combination with AZTH, as an antiviral treatment for COVID-19 in humans.

Timing of antiviral treatment initiation is critical to reduce SARS-Cov-2 viral load (preprint)

We modeled the viral dynamics of 13 untreated patients infected with SARS-CoV-2 to infer viral growth parameters and predict the effects of antiviral treatments. In order to reduce peak viral load by more than 2 logs, drug efficacy needs to be greater than 80% if treatment is administered after symptom onset; an efficacy of 50% could be sufficient if treatment is initiated before symptom onset. Given their pharmacokinetic/pharmacodynamic properties, current investigated drugs may be in a range of 20-70% efficacy. They may help control virus if administered very early, but may not have a major effect in severe patients.