Vitamin C is very essential to humans. It is a powerful antioxidant that contributes to the immune system of our body by supporting multiple cellular functions. Deficiency of this essential nutrient in our body can lead to impaired immunity and symptoms such as rough skin, weakness, anaemia and swollen joints.
The main function of vitamin C is to protect against pathogens and promote scavenging activity in the body. Free radicals scavenging is very important to save cells from the damage of free radicals. Vitamin C is also very effective to prevent and treat respiratory infections. 
Vitamin C is linked to several inflammatory processes and immunity. It helps in the production and function of white blood cells and fights against several inflammatory diseases. Not only this, but vitamin C is also known to have antiviral and antibacterial roles. 
A study published in the Journal of The Royal Society of Medicine says that vitamin C increases the functioning of T-cells in our body and decreases the multiplication of viruses. It also increases resistance against multiple viral and bacterial infections like pneumonia. 
Drop in the levels of vitamin C in our body can lead to acute bronchitis and pneumonia and other lung infections. Therefore, it is essential to maintain a sufficient dosage of vitamin C in the body i.e. 75 mg for adult women and 90 mg for adult men.
Another study suggests that pneumonia reduced to around 80% in people who were administered with dietary vitamin C intake. Also, the incidence of common cold decreased by an average of 50%. 
Coronavirus causes accumulation of fluids in the lungs and destroys the alveolar capillaries. A clinical trial study carried out in February 2020 suggests that vitamin C helps to eliminate alveolar fluid and prevent its further accumulation thus, reducing damage to the lungs. It also helps prevent the common cold and shows protective effects on patients who have influenza. 
According to a Journal of Antimicrobial Chemotherapy, vitamin C has reduced the severity and duration of the common cold in humans as well as decreased viral respiratory infections. In three controlled trials, vitamin C has shown its effectiveness in lowering the incidence of pneumonia and respiratory tract infection caused due to Severe Acute Respiratory Syndrome (SARS). 
Vitamin C has a lot of health benefits but saying that it completely helps cure COVID-19 would be wrong. Though several clinical trials say that vitamin C boosts the immune system and help fight against coronavirus, the study needs further evidence to prove it.
Till then, the most effective way to prevent the spread of the infection is to maintain good hand hygiene and self-isolation until there's no particular vaccine developed.
Doctors and scientists across the world are in a mad dash to discover an effective vaccine or treatment method for the COVID-19. They are testing several existing antimalarials, antivirals and Unani drugs to see if they can combat the effect of COVID-19.
There have been several theories coming out every day claiming to be a cure for coronavirus. However, there has not been any scientific evidence to prove them all. On the other hand, a report based on Dr Andrew G. Weber (New York) says that people are recovering at a faster rate after receiving vitamin C intravenously compared to people who do not receive the dose. The revelation is done based on a study that says vitamin C has beneficial effects on the infections, blood pressure and bronchoconstriction and tend to shorten the stay period of the patient in the ICU.