Taking formulated vitamins will not protect you against COVID-19.
Several agents (including vitamin C, hydroquinone and antivirals) are currently being tested for their effects in COVID-19, but no trustworthy confirmatory data are available as yet.
A diet rich in fresh vegetables and fruit is generally recommended at all times – not just during COVID-19 – to help your body maintain a working immune system. Fresh vegetables and fruits contain a much broader range of necessary nutrients than vitamin pills. Therefore, it is always better to eat a lot of fresh vegetables and fruit than trying to compensate with formulated nutrients.
Having said that, some individuals might indeed lack specific vitamins or (micro-)nutrients.
In this case, your GP or attending physician will be able to offer advice.
When taking formulated vitamins, please make sure your intake does not exceed the recommended daily dosage. Some vitamins might harm you if taken in too high doses, and some supplements can interact negatively with your heart medicines.