The emergence of a novel coronavirus(SARS-CoV-2) in late 2019 has resulted in a global epidemic of the infectious condition COVID-19. Since March 2022, the Omicron mutant has caused widespread transmission in Shanghai, China, and is characterized by the majority of asymptomatic patients. Although showing no obvious symptoms, the asymptomatic patients have high transmissibility because of high viral loads in their oropharynx and nasopharynx. Therefore，this study puts forwards the hypothesis that local flushing treatment in the sino-nasal and mouth cavity can reduce the viral load to reduce their transmissibility.

Nasal Irrigation and gargling is a safe and commonly used mechanism to treat a variety of sinonasal diseases including sinusitis, rhinitis, and upper respiratory tract infections. Povidone-iodine(PVP-I) is a water-soluble complex of povidone, a carrier molecule, and iodine, which has powerful microbicidal activity. Also, recent evidence of in-vitro virucidal action of povidone-iodine in Severe Acute Respiratory Syndrome-Coronavirus 2 (SARS CoV-2) has been supported.

Therefore, the study is designed to assess the virucidal effect of nasal irrigation and gargling with PVP-I against SARS-CoV-2 located in the throat. The hypothesis was that the treatment would be effective in improving the negative conversion rate of SARS-CoV-2 nucleic acid on day 10.

The purpose of the study is to evaluate if using nasal irrigation and gargling with PVP-I and hypertonic saline solution, can improve the negative conversion rate of SARS-CoV-2 nucleic acid on day 10 and reduce the incidence rate and severity of symptoms associated with COVID-19.

The study is a prospective, single-center, open-label, randomized controlled trial. The subjects who met the inclusion criteria were stratified according to gender, and randomly divided into control group and experimental group. Both groups were treated according to the diagnosis and treatment for novel coronavirus pneumonia (Trial Nine Edition). Of them, the control group is as blank control, and the experimental group was rinsed with PVP-I containing hypertonic lotion prepared by 0.9% Normal saline（NS）, 10% sodium chloride（NaCl）, and povidone-iodine（PVP-I） gargle four times a day.

The participants in the control group and the experimental group will be required to fill in a daily record and report the main complaint of discomfort. The subjects in the experimental group are also asked to record the implementation of oral and nasal flushing every day.

The researchers are going to record the test results of novel coronavirus nucleic acid samples from the nasopharynx of all subjects in the control group and the experimental group every day.

Inclusion Criteria:

• Patients nucleic acid testing positive for COVID-19.
• Diagnose as asymptomatic patients infected by COVID-19, and receive medical observation at a Fang Chang Hospital.
• Be able to understand this study, willing to participate in, and sign the informed consent form.
• Commit to follow the research procedures and cooperate in the implementation of the whole process research.
• Can communicate with researchers through smart phones.

Exclusion Criteria:

• The nucleic acid test result of novel coronavirus has always been negative after entering the Fang Chang Hospital.
• patients who have history of nasal surgery, or current use of nasal saline irrigation or other intranasal medications.
• Patients with thyroid diseases , respiratory diseases or other serious basic diseases.
• Allergy to iodine.
• Participation in another prospective COVID related research project(clinical trial).
• Pregnancy or lactation
• Patients with immune deficiency (such as patients with malignant tumors, organ or bone marrow transplantation, patients with AIDS, and those taking immunosuppressive drugs within 3 months before screening).
• Other patients considered unsuitable by the investigator to participate in this study