Decreased community-acquired pneumonia coincided with rising awareness of precautions before governmental containment policy in Japan.

The effectiveness of population-wide compliance to personal precautions (mask-wearing and hand hygiene) in preventing community-acquired pneumonia has been unknown. In Japan, different types of nonpharmaceutical interventions from personal precautions to containment and closure policies (CACPs, e.g. stay-at-home requests) were sequentially introduced from late January to April 2020, allowing for separate analysis of the effects of personal precautions from other more stringent interventions. We quantified the reduction in community-acquired pneumonia hospitalizations and deaths and assessed if it coincided with the timing of increased public awareness of personal precautions before CACPs were implemented. A quasi-experimental interrupted time-series design was applied to non-COVID-19 pneumonia hospitalization and 30-day death data from April 2015 to August 2020 across Japan to identify any trend changes between February and April 2020. We also performed a comparative analysis of pyelonephritis and biliary tract infections to account for possible changes in the baseline medical attendance. These trend changes were then compared with multiple indicators of public awareness and behaviors related to personal precautions, including keyword usage in mass media coverage and sales of masks and hand hygiene products. Hospitalizations and 30-day deaths from non-COVID-19 pneumonia dropped by 24.3% (95% CI 14.8-32.8) and 16.1% (5.5-25.5), respectively, in February 2020, before the implementation of CACPs, whereas pyelonephritis and biliary tract infections did not suggest a detectable change. These changes coincided with increases in indicators related to personal precautions rather than those related to contact behavior changes. Community-acquired pneumonia could be reduced by population-wide compliance to moderate precautionary measures.

A Multicenter Randomized Controlled Trial To Evaluate the Efficacy and Safety of Nelfinavir in Patients with Mild COVID-19.

Nelfinavir, an orally administered inhibitor of human immunodeficiency virus protease, inhibits the replication of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in vitro. We conducted a randomized controlled trial to evaluate the clinical efficacy and safety of nelfinavir in patients with SARS-CoV-2 infection. We included unvaccinated asymptomatic or mildly symptomatic adult patients who tested positive for SARS-CoV-2 infection within 3 days before enrollment. The patients were randomly assigned (1:1) to receive oral nelfinavir (750 mg; thrice daily for 14 days) combined with standard-of-care or standard-of-care alone. The primary endpoint was the time to viral clearance, confirmed using quantitative reverse-transcription PCR by assessors blinded to the assigned treatment. A total of 123 patients (63 in the nelfinavir group and 60 in the control group) were included. The median time to viral clearance was 8.0 (95% confidence interval [CI], 7.0 to 12.0) days in the nelfinavir group and 8.0 (95% CI, 7.0 to 10.0) days in the control group, with no significant difference between the treatment groups (hazard ratio, 0.815; 95% CI, 0.563 to 1.182; P = 0.1870). Adverse events were reported in 47 (74.6%) and 20 (33.3%) patients in the nelfinavir and control groups, respectively. The most common adverse event in the nelfinavir group was diarrhea (49.2%). Nelfinavir did not reduce the time to viral clearance in this setting. Our findings indicate that nelfinavir should not be recommended in asymptomatic or mildly symptomatic patients infected with SARS-CoV-2. The study is registered with the Japan Registry of Clinical Trials (jRCT2071200023). IMPORTANCE The anti-HIV drug nelfinavir suppresses the replication of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in vitro. However, its efficacy in patients with COVID-19 has not been studied. We conducted a multicenter, randomized controlled trial to evaluate the efficacy and safety of orally administered nelfinavir in patients with asymptomatic or mildly symptomatic COVID-19. Compared to standard-of-care alone, nelfinavir (750 mg, thrice daily) did not reduce the time to viral clearance, viral load, or the time to resolution of symptoms. More patients had adverse events in the nelfinavir group than in the control group (74.6% [47/63 patients] versus 33.3% [20/60 patients]). Our clinical study provides evidence that nelfinavir, despite its antiviral effects on SARS-CoV-2 in vitro, should not be recommended for the treatment of patients with COVID-19 having no or mild symptoms.

Serological response to a third dose of SARS-CoV-2 vaccine according to previous infection history

The IgG antibody titer against SARS-CoV-2 receptor binding protein (RBD) after mRNA vaccine were compared between those with and without previous infection (PI) for up to 48 weeks. Though sustained higher IgG-RBD were observed in the PI group after two doses of vaccines, both groups benefited from the booster shots of the third vaccine. This data supports the necessity of the booster shots to those with PI.

Gargle sample is an effective option in a novel fully automated molecular point-of-care test for influenza: a multicenter study.

BACKGROUND: We conducted a multicenter study to evaluate the performance of a novel fully automated molecular point-of-care test using transcription-reverse transcription concerted reaction that can detect influenza A and B within 15 min in nasopharyngeal swabs and gargle samples (TRCsatFLU). METHODS: Patients who visited or were hospitalized at eight clinics and hospitals with influenza-like illnesses between December 2019 and March 2020 participated in this study. We collected nasopharyngeal swabs from all patients and gargle samples from patients whom the physician judged fit to perform gargling. The result of TRCsatFLU was compared to a conventional reverse transcription-polymerase chain reaction (RT-PCR). If the results of TRCsatFLU and conventional RT-PCR were different, the samples were analyzed by sequencing. RESULTS: We evaluated 233 nasopharyngeal swabs and 213 gargle samples from 244 patients. The average age of the patients was 39.3 ± 21.2. Of the patients, 68.9% visited a hospital within 24 h of symptom onset. The most common symptoms were fever (93.0%), fatigue (79.5%), and nasal discharge (64.8%). All patients in whom the gargle sample was not collected were children. Influenza A or B was detected in 98 and 99 patients in nasopharyngeal swabs and gargle samples using TRCsatFLU, respectively. Four and five patients in nasopharyngeal swabs and gargle samples, respectively, with different TRCsatFLU and conventional RT-PCR results. Influenza A or B was detected using sequencing in all samples with different results. Based on the combined conventional RT-PCR and sequencing results, the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of TRCsatFLU for influenza detection in nasopharyngeal swabs were 0.990, 1.000, 1.000, and 0.993, respectively. In the gargle samples, the sensitivity, specificity, PPV, and NPV of the TRCsatFLU for detecting influenza were 0.971, 1.000, 1.000, and 0.974, respectively. CONCLUSIONS: The TRCsatFLU showed great sensitivity and specificity for the detection of influenza in nasopharyngeal swabs and gargle samples. TRIAL REGISTRATION: This study was registered in the UMIN Clinical Trials Registry (reference number: UMIN000038276) on October 11, 2019. Before sample collection, written informed consent for the participation and publication of this study was obtained from all participants.

Serological response to a third dose of SARS-CoV-2 vaccine according to previous infection history.

The IgG antibody titer against SARS-CoV-2 receptor binding protein (RBD) after mRNA vaccine were compared between those with and without previous infection (PI) for up to 48 weeks. Though sustained higher IgG-RBD were observed in the PI group after two doses of vaccines, both groups benefited from the booster shots of the third vaccine. This data supports the necessity of the booster shots to those with PI.

Clinical evaluation of a fully automated and high-throughput molecular testing system for detection of influenza virus.

INTRODUCTION: We investigated the performance of the cobas® 6800 system and cobas SARS-CoV-2 & Influenza A/B, a fully automated molecular testing system for influenza viruses and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This enabled an assay in a batch of 96 samples in approximately 3 h. METHODS: An assay was performed using the cobas SARS-CoV-2 & Influenza A/B on the cobas 6800 system for samples collected in four facilities between November 2019 and March 2020 in our previous study. The results were compared with those obtained using the reference methods. RESULTS: Of the 127 samples analyzed, the cobas SARS-CoV-2 & Influenza A/B detected influenza A virus in 75 samples, of which 73 were positive using the reference methods. No false negative results were observed. The overall positive and negative percent agreement for influenza A virus detection were 100.0% and 96.3%, respectively. There were no positive results for the influenza B virus or SARS-CoV-2. CONCLUSION: The cobas 6800 system and cobas SARS-CoV-2 & Influenza A/B showed high accuracy for influenza A virus detection and can be useful for clinical laboratories, especially those that routinely assay many samples.

SARS-CoV-2 seroprevalence and infection rate in Manila, Philippines prior to national vaccination program implementation: a repeated cross-sectional analysis.

BACKGROUND: SARS-CoV-2 seroepidemiological studies are used to guide public health decision making and to prepare for emerging infectious diseases. Disease occurrence estimates are limited in the Philippines, the country with the highest reported number of coronavirus disease-related deaths in the Western Pacific region. We aimed to estimate SARS-CoV-2 seroprevalence and infection rate among outpatient clinic attendees in Metro Manila prior to the implementation of the national coronavirus disease vaccination program. METHODS: We conducted repeated cross-sectional surveys at the animal bite clinic in San Lazaro Hospital, Manila, the Philippines across four periods, 3 months apart, between May 2020 and March 2021. Multivariable logistic regression was used to assess associations between different characteristics and infection status including seropositivity. RESULTS: In total 615 participants were enrolled, ranging from 115 to 174 per period. Seroprevalence quadrupled between the first (11.3%) and second (46.8%) periods and plateaued thereafter (third-46.0%, fourth-44.6%). Among seropositive participants, total antibody concentration was comparable throughout the first to third periods but declined between the third and fourth periods. Infection prevalence was comparable across enrollment periods (range 2.9-9.5%). Post-secondary education [aOR 0.42 (95% CI 0.26, 0.67)] was protective, and frontline work [aOR 1.81 (95% CI 1.18, 2.80)] was associated with increased odds of seropositivity. Frontline work status [aOR 2.27 (95% CI 1.10, 4.75)] and large household size [aOR 2.45 (95% CI 1.18, 5.49)] were associated with increased odds of infection. CONCLUSIONS: The quadrupling of seroprevalence over 3 months between the first and second enrollment periods coincided with the high burden of infection in Metro Manila in early 2020. Our findings suggest a limit to the rise and potential decline of population-level SARS-CoV-2 infection-induced immunity without introduction of vaccines. These results may add to our understanding of how immunity develops against emerging infectious diseases including coronaviruses.

Evaluation of a Triage Checklist for Mild COVID-19 Outpatients in Predicting Subsequent Emergency Department Visits and Hospitalization during the Isolation Period: A Single-Center Retrospective Study.

Managing mild illness in COVID-19 and predicting progression to severe disease are concerning issues. Here, we investigated the outcomes of Japanese patients with mild COVID-19, and identified triage risk factors for further hospitalization and emergency department (ED) visits at a single tertiary hospital. A triage checklist with 30 factors was used. Patients recommended for isolation were followed up for 10 days for subsequent ED visits or hospital admission. Overall, 338 patients (median age, 44.0; 45% women) visited the clinic 5.0 days (median) after symptom onset. Thirty-six patients were immediately hospitalized following triage; others were isolated. In total, 72 non-hospitalized patients visited the ED during their isolation, and 30 were hospitalized after evaluation for oxygen desaturation. The median ED visit and hospitalization durations after symptom onset were 5.0 and 8.0 days, respectively. The checklist factors associated with hospitalization during isolation were age > 50 years, body mass index > 25 kg/m2, hypertension, tachycardia with pulse rate > 100/min or blood pressure > 135 mmHg at triage, and >3-day delay in hospital visit after symptom onset. No patients died. Altogether, 80% of patients with mild COVID-19 could be safely isolated at home. Age, BMI, underlying hypertension, date after symptom onset, tachycardia, and systolic blood pressure at triage might be related to later hospitalization.

Efficacy of Lactococcus lactis strain plasma (LC-Plasma) in easing symptoms in patients with mild COVID-19: protocol for an exploratory, multicentre, double-blinded, randomised controlled trial (PLATEAU study).

INTRODUCTION: The COVID-19 pandemic has been a major concern worldwide; however, easily accessible treatment options for patients with mild COVID-19 remain limited. Since the oral intake of Lactococcus lactis strain plasma (LC-Plasma) enhances both the innate and acquired immune systems through the activation of plasmacytoid dendritic cells (pDCs), we hypothesised that the oral intake of LC-Plasma could aid the relief or prevention of symptoms in patients with asymptomatic or mild COVID-19. METHODS AND ANALYSIS: This is an exploratory, multicentre, double-blinded, randomised, placebo-controlled trial. This study was initiated in December 2021 and concludes in April 2023. The planned number of enrolled subjects is 100 (50 subjects×2 groups); subject enrolment will be conducted until October 2022. Patients with asymptomatic or mild COVID-19 will be enrolled and randomly assigned in a 1:1 ratio to group A (oral intake of LC-Plasma-containing capsule, 200 mg/day, for 14 days) or group B (oral intake of placebo capsule, for 14 days). The primary endpoint is the change in subjective symptoms measured by the severity score. Secondary endpoints include SARS-CoV-2 viral loads, biomarkers for pDC activation, serum SARS-CoV-2-specific antibodies, serum cytokines, interferon and interferon-inducible antiviral effectors and the proportion of subjects with emergency room visits to medical institutions or who are hospitalised. ETHICS AND DISSEMINATION: The study protocol was approved by the Clinical Research Review Board of Nagasaki University, in accordance with the Clinical Trials Act of Japan. The study will be conducted in accordance with the Declaration of Helsinki, the Clinical Trials Act, and other current legal regulations in Japan. Written informed consent will be obtained from all the participants. The results of this study will be reported in journal publications. TRIAL REGISTRATION NUMBER: Japan Registry of Clinical Trials (registration number: jRCTs071210097).

Preexisting Humoral Immunity Cross-Reacting with SARS-CoV-2 Might Prevent Death Due to COVID-19 in Critical Patients.

The preexistence of humoral immunity, which cross-reacts with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) protein due to prior endemic low-pathogenic human coronavirus infection, has been reported, but its role in coronavirus disease 2019 (COVID-19) outcomes remains elusive. We evaluated serum samples obtained from 368 patients before the pandemic and 1423 independent serum samples from patients during the pandemic. We found that approximately 6~13% and 1.5% of patients had IgG cross-reactivity to the SARS-CoV-2 spike and nucleocapsid proteins in both cohorts. We evaluated the IgG cross-reactivity to the SARS-CoV-2 spike and nucleocapsid proteins in 48 severe or critical COVID-19 patients to evaluate if the elevation of IgG was evoked as a primary response (IgG elevation from 10 days after antigen exposure) or boosted as a secondary response (IgG elevation immediately after antigen exposure). Approximately 50% of patients showed humoral immune responses to the nucleocapsid protein of SARS-CoV-2. Importantly, none of the critically ill patients with this humoral immunity died, whereas 40% of patients without this immunity did. Taken together, subjects had humoral immunity to SARS-CoV-2 nucleocapsid but not spike before the pandemic, which might prevent critically ill COVID-19 patients from dying.

Unique Evolution of SARS-CoV-2 in the Second Large Cruise Ship Cluster in Japan.

In the initial phase of the novel coronavirus disease (COVID-19) pandemic, a large-scale cluster on the cruise ship Diamond Princess (DP) emerged in Japan. Genetic analysis of the DP strains has provided important information for elucidating the possible transmission process of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on a cruise ship. However, genome-based analyses of SARS-CoV-2 detected in large-scale cruise ship clusters other than the DP cluster have rarely been reported. In the present study, whole-genome sequences of 94 SARS-CoV-2 strains detected in the second large cruise ship cluster, which emerged on the Costa Atlantica (CA) in Japan, were characterized to understand the evolution of the virus in a crowded and confined place. Phylogenetic and haplotype network analysis indicated that the CA strains were derived from a common ancestral strain introduced on the CA cruise ship and spread in a superspreading event-like manner, resulting in several mutations that might have affected viral characteristics, including the P681H substitution in the spike protein. Moreover, there were significant genetic distances between CA strains and other strains isolated in different environments, such as cities under lockdown. These results provide new insights into the unique evolution patterns of SARS-CoV-2 in the CA cruise ship cluster.

Performance of anti-SARS-CoV-2 antibody testing in asymptomatic or mild COVID-19 patients: A retrospective study in outbreak on a cruise ship.

OBJECTIVES: A few studies on antibody testing have focused on asymptomatic or mild coronavirus disease 2019 (COVID-19) patients with low initial anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody responses. Anti-SARS-CoV-2 antibody-testing performance was evaluated using blood samples from asymptomatic or mild COVID-19 patients. METHODS: Blood samples were collected from 143 COVID-19 patients during an outbreak on a cruise ship 3 weeks after diagnosis. Simultaneously, a follow-up SARS-CoV-2 genetic test was performed. Samples stored before the COVID-19 pandemic were also used to evaluate the lateral flow immunochromatographic assay (LFA) and electrochemiluminescence immunoassay (ECLIA). Titers of anti-SARS-CoV-2 IgM and IgG antibodies against the nucleocapsid and spike proteins were measured using the enzyme-linked immunosorbent assay to confirm which antibodies were influenced on LFA- and ECLIA- false-negative result in crew-member samples. RESULTS: Sensitivity, specificity, positive-predictive, and negative-predictive values of LFA-detected IgM antibodies were 0.231, 1.000, 1.000, and 0.613, respectively; those of LFA-detected IgG antibodies were 0.483, 0.989, 0.972, and 0.601, respectively; and those of ECLIA-detected total antibodies were 0.783, 1.000, 1.000, and 0.848, respectively. All antibody titers measured using ELISA were significantly lower in blood samples with negative results than in those with positive results in both LFA and ECLIA. In the patients with negative results from the follow-up genetic testing, IgM-, IgG-, and total-antibody positivity rates were 22.9%, 47.6%, and 72.4%, respectively. CONCLUSIONS: These findings suggest that anti-SARS-CoV-2 antibody testing has lower performance in asymptomatic or mild COVID-19 patients than required in the guidelines.

Efficacy of clarithromycin in patients with mild COVID-19 pneumonia not receiving oxygen administration: protocol for an exploratory, multicentre, open-label, randomised controlled trial (CAME COVID-19 study).

INTRODUCTION: The COVID-19 pandemic has emerged worldwide. Although several medications have been approved for treating moderate-to-severe COVID-19, very few treatment strategy has been established for patients with mild COVID-19 who do not require oxygen administration. Clarithromycin is a macrolide antimicrobial agent that has been widely used for bacterial respiratory infectious diseases. Clarithromycin also acts an immunomodulating drug and suppresses cytokine storms in viral respiratory diseases, including influenza. In this study, we aim to evaluate the efficacy of clarithromycin in patients with mild COVID-19. METHODS AND ANALYSIS: This is an exploratory, multicentre, open-label, randomised controlled trial. This study was initiated in May 2021 and will end in July 2022. Patients with mild COVID-19 pneumonia who do not require oxygen administration will be enrolled and randomly assigned in a 1:1:1 ratio to group A (administration of clarithromycin 800 mg/day), group B (administration of clarithromycin 400 mg/day) or group C (standard treatment without clarithromycin). The planned number of enrolled patients is 60 (20 patients × three groups). The primary endpoint is the number of days required to improve the clinical symptoms as measured by the severity score. Secondary endpoints include days for recovery of the body temperature, proportion of patients with oxygen administration, inflammatory cytokines, viral load, serum immunoglobulins, peripheral blood lymphocytes, blood biomarkers and pneumonia infiltrations. ETHICS AND DISSEMINATION: The study protocol was approved by the Clinical Research Review Board of Nagasaki University in accordance with the Clinical Trials Act in Japan. The study will be conducted in accordance with the Declaration of Helsinki, the Clinical Trials Act and other current legal regulations in Japan. Written informed consent will be obtained from all the participants. The results of this study will be reported as journal publications. TRIAL REGISTRATION NUMBER: jRCTs071210011.

Epidemiology of Coronavirus Disease Outbreak among Crewmembers on Cruise Ship, Nagasaki City, Japan, April 2020.

In April 2020, a coronavirus disease (COVID-19) outbreak occurred on the cruise ship Costa Atlantica in Nagasaki, Japan. Our outbreak investigation included 623 multinational crewmembers onboard on April 20. Median age was 31 years; 84% were men. Each crewmember was isolated or quarantined in a single room inside the ship, and monitoring of health status was supported by a remote health monitoring system. Crewmembers with more severe illness were hospitalized. The investigation found that the outbreak started in late March and peaked in late April, resulting in 149 laboratory-confirmed and 107 probable cases of infection with severe acute respiratory syndrome coronavirus 2. Six case-patients were hospitalized for COVID-19 pneumonia, including 1 in severe condition and 2 who required oxygen administration, but no deaths occurred. Although the virus can spread rapidly on a cruise ship, we describe how prompt isolation and quarantine combined with a sensitive syndromic surveillance system can control a COVID-19 outbreak.

Evaluation of a novel rapid TRC assay for the detection of influenza using nasopharyngeal swabs and gargle samples.

We evaluated a novel transcription-reverse transcription concerted reaction (TRC) assay that can detect influenza A and B within 15 min using nasopharyngeal swab and gargle samples obtained from patients with influenza-like illness, between January and March 2018 and between January and March 2019. Based on the combined RT-PCR and sequencing results, in the nasal swabs, the sensitivity and specificity of TRC for detecting influenza were calculated as 1.000 and 1.000, respectively. In the gargle samples, the sensitivity and specificity of TRC were 0.946 and 1.000, respectively. The TRC assay showed comparable performance to RT-PCR in the detection of influenza viruses.

Discrepancy of SARS-CoV-2 PCR results due to the sample collection sites and possible improper sampling.

Polymerase chain reaction (PCR) testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is necessary for confirming a diagnosis of Coronavirus disease 2019 (COVID-19). Here we present a COVID-19 case of an elderly woman whose SARS-CoV-2 PCR tests showed false negative repeatedly by evaluating with different sampling sites and procedures. Nasopharyngeal swabs, suctioned sputum, and tongue swabs were collected for SARS-CoV-2-PCR. As for tongue swabs, we compared between two different sample conditions; one obtained with dry condition and the other obtained with moistened condition inside the oral cavity. SARS-CoV-2-PCR showed positive for an extended period with suctioned sputum samples compared with nasopharyngeal swabs and tongue swabs. No SARS-CoV-2 from a nasopharyngeal swab sample obtained on day 46 after symptoms onset was isolated despite high viral load (183740.5 copies/5µL). An adequate production of neutralizing antibody in a serum sample on day 46 was also confirmed. The number of RNA copies of the tongue swab samples was higher with moistened condition than with dry condition. The present case suggests that the difference of sampling site or sample condition can affect PCR results. High loads viral RNA detection does not always correlate with infectivity.

Detection of SARS-CoV-2 using qRT-PCR in saliva obtained from asymptomatic or mild COVID-19 patients, comparative analysis with matched nasopharyngeal samples.

OBJECTIVES: The accurate detection of severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) is essential for the diagnosis of coronavirus disease 2019 (COVID-19). We compared the quantitative RT-PCR results between nasopharyngeal swabs and saliva specimens. METHODS: A COVID-19 outbreak occurred on a cruise ship at Nagasaki port, Japan. We obtained 123 nasopharyngeal swabs and saliva each from asymptomatic or mild patients in the late phase of infection. RESULTS: The intervals from the diagnosis to the sampling were 25.5 days for nasopharyngeal swabs and 28.9 days for saliva. The positive rate was 19.5% (24/123) for nasopharyngeal swabs and 38.2% (47/123) for saliva (P = 0.48). The quantified viral copies (mean ± SEM copies/5 µl) were 9.3±2.6 in nasopharyngeal swabs and 920±850 in saliva (P = 0.0006). CONCLUSIONS: The advantages of saliva specimens include positive rate improvement and accurate viral load detection. Saliva may be used as a reliable sample for SARS-CoV-2 detection.

Efficacy and safety of nelfinavir in asymptomatic and mild COVID-19 patients: a structured summary of a study protocol for a multicenter, randomized controlled trial.

OBJECTIVES: The aim of this trial is to evaluate the antiviral efficacy, clinical efficacy, and safety of nelfinavir in patients with asymptomatic and mild COVID-19. TRIAL DESIGN: The study is designed as a multicenter, open-label, blinded outcome assessment, parallel group, investigator-initiated, exploratory, randomized (1:1 ratio) controlled clinical trial. PARTICIPANTS: Asymptomatic and mild COVID-19 patients will be enrolled in 10 university and teaching hospitals in Japan. The inclusion and exclusion criteria are as follows: Inclusion criteria: (1) Japanese male or female patients aged ≥ 20 years (2) SARS-CoV-2 detected from a respiratory tract specimen (e.g., nasopharyngeal swab or saliva) using PCR, LAMP, or an antigen test within 3 days before obtaining the informed consent (3) Provide informed consent Exclusion criteria: (1) Symptoms developed ≥ 8 days prior to enrolment (2) SpO2 < 96 % (room air) (3) Any of the following screening criteria: a) ALT or AST ≥ 5 × upper limit of the reference range b) Child-Pugh class B or C c) Serum creatinine ≥ 2 × upper limit of the reference range and creatinine clearance < 30 mL/min (4) Poorly controlled diabetes (random blood glucose ≥ 200 mg/dL or HbA1c ≥ 7.0%, despite treatment) (5) Unsuitable serious complications based on the assessment of either the principal investigator or the sub-investigator (6) Hemophiliac or patients with a marked hemorrhagic tendency (7) Severe diarrhea (8) Hypersensitivity to the investigational drug (9) Breastfeeding or pregnancy (10) With childbearing potential and rejecting contraceptive methods during the study period from the initial administration of the investigational drug (11) Receiving rifampicin within the previous 2 weeks (12) Participated in other clinical trials and received drugs within the previous 12 weeks (13) Undergoing treatment for HIV infection (14) History of SARS-CoV-2 vaccination or wishes to be vaccinated against SARS-CoV-2 (15) Deemed inappropriate (for miscellaneous reasons) based on the assessment of either the principal investigator or the sub-investigator INTERVENTION AND COMPARATOR: Patients who meet the inclusion criteria and do not meet any of the exclusion criteria will be randomized to either the nelfinavir group or the symptomatic treatment group. The nelfinavir group will be administered 750 mg of nelfinavir orally, three times daily for 14 days (treatment period). However, if a participant tests negative on two consecutive PCR tests of saliva samples, administration of the investigational drug for that participant can be discontinued at the discretion of the investigators. The symptomatic treatment group will not be administered the investigational drug, but all other study procedures and conditions will be the same for both groups for the duration of the treatment period. After the treatment period of 14 days, each group will be followed up for 14 days (observational period). MAIN OUTCOMES: The primary endpoint is the time to negative conversion of SARS-CoV-2. During the study period from Day 1 to Day 28, two consecutive negative PCR results of saliva samples will be considered as the negative conversion of the virus. The secondary efficacy endpoints are as follows: For patients with both asymptomatic and mild disease: area under the curve of viral load, half decay period of viral load, body temperature at each time point, all-cause mortality, incidence rate of pneumonia, percentage of patients with newly developed pneumonia, rate of oxygen administration, and the percentage of patients who require oxygen administration. For asymptomatic patients: incidence of symptomatic COVID-19, incidence of fever (≥ 37.0 °C for two consecutive days), incidence of cough For patients with mild disease: incidence of defervescence (< 37.0 °C), incidence of recovery from clinical symptoms, incidence of improvement of each symptom The secondary safety endpoints are adverse events and clinical examinations. RANDOMIZATION: Patients will be randomized to either the nelfinavir group or the symptomatic treatment group using the electric data capture system (1:1 ratio, dynamic allocation based on severity [asymptomatic], and age [< 60 years]). BLINDING (MASKING): Only the assessors of the primary outcome will be blinded (blinded outcome assessment). NUMBERS TO BE RANDOMIZED (SAMPLE SIZE): The sample size was determined based on our power analysis to reject the null hypothesis, S (t | z =1) = S (t | z = 0) where S is a survival function, t is time to negative conversion, and z denotes randomization group, by the log-rank test with a two-sided p value of 0.05. We estimated viral dynamic parameters by fitting a nonlinear mixed-effects model to reported viral load data, and simulated our primary endpoint from viral-load time-courses that were realized from sets of viral dynamics parameters sampled from the estimated probability distribution of the parameters (sample size: 2000; 1000 each for randomization group). From this estimation of the hazard ratio between the randomization groups for the event of negative conversion using this simulation dataset, the required number of events for rejecting our null hypothesis with a power of 0.80 felled 97.345 by plugging the estimated hazard ratio, 1.79, in Freedman's equation. Therefore, we decided the required number of randomizations to be 120 after consideration of the frequency of censoring and the anticipated rate of withdrawal caused by factors such as withdrawal of consent. TRIAL STATUS: Protocol version 6.0 of February 12, 2021. Recruitment started on July 22, 2020 and is anticipated to be completed by March 31, 2022. TRIAL REGISTRATION: This trial was registered in Japan Registry of Clinical Trials (jRCT) ( jRCT2071200023 ) on 21 July 21, 2020. FULL PROTOCOL: The full protocol is attached as an additional file, accessible from the Trials website (Additional file 1). In the interest in expediting dissemination of this material, the familiar formatting has been eliminated; this Letter serves as a summary of the key elements of the full protocol. The study protocol has been reported in accordance with the Standard Protocol Items: Recommendations for Clinical Interventional Trials (SPIRIT) guidelines (Additional file 2).