You should try Giloy( Tinospora Cordifolia ) which is an amazing herb and I have personally used it and felt the difference after taking it regularly. The good part about this herb is that it can be grown in your home very easily and with less maintenance. This herb is also popularly known as "root of immortality". The stem and root both can be consumed either in the form of smoothie or juice. But stem has its most utility as compared to its root.
Giloy has tremendous potential to boost immunity. It is also known to be very rich in antioxidants which can fight free radicals. It keeps the cell healthy, improve immunity power and keeps the health free from diseases. It further helps to remove toxins, purifies blood, fights bacteria that causes diseases and also combats liver diseases and urinary tract infections. It can also be utilized in treating heart related diseases and infertility.
As simple as it sounds, garlic is one of the best ways to boost immunity. It's as easy as adding some garlic juice extract to whatever the mix.
Another super healthy drink is the hibiscus plant, popularly know as Zobo in Africa. The mix of ginger and zobo leaf is both healthy and tasty. I think that's a win.
Garlic; Experiments have shown that garlic — or specific chemical compounds found in garlic — is highly effective at killing countless microorganisms.
Hibiscus plant; Research has also uncovered a range of health benefits linked to drinking hibiscus tea, showing that it may lower blood pressure, fight bacteria and even aid weight loss.
Personally, I have a couple of different things that I like to drink when I am trying to fight off a cold or when I feel like one is coming on and I want to knock it out before it turns into something worse.
The first thing I drink is Airborne. It is basically just a bunch of vitamins and minerals in tablet form. You dissolve it in water and then you drink it. I am not really sure if it does a great job and it is pretty expensive, but it makes me feel better about what I am doing, so maybe it is all just psychosomatic.
The other two things I like to drink are very easy and very cheap. Green Tea and Black Tea are two of my favorite drinks. I can drink them cold or hot. Usually if I am fighting off something or preparing to fight off something it is Winter and I am cold so I drink them hot. They both have antioxidants in them and a lot of other beneficial health effects. The only thing I don't like about them is they are diuretics so they make me have to pee a lot.
I think if you started drinking black or green tea you would start seeing health benefits even if you weren't getting sick or trying to fight off something. The biggest advice I can give though is make sure you have a full stomach. I don't know if you have ever tried to take a vitamin or pill when you have an empty stomach. The effects can be pretty horrible. I tend to get nauseous and light headed. The same thing can happen if I drink tea before I have some food in my stomach. I don't know if it is the caffeine or what, but it seems to really have an adverse effect on me which can sometimes be worse than the actual thing that I am trying to fight off.
Seeing who wrote the question, I am sure you are familiar with the benefits, but if you are reading this answer and you are not, I encourage you to do a Google search on Green Tea and Black Tea to get a full picture of all the benefits that they offer.
Green juice aka green juice
This juice is not only full of vitamins and can strengthen the body's immunity, but it also tastes good.
Spinach is referred to as 'superfood' because it contains lots of vitamins and minerals, such as Vitamin C, and high content of beta-carotene and antioxidants that help the body fight infections and viruses.
Oranges are rich in Vitamin C which is important for fighting flu and fever.
Celery also contains Vitamin C and antioxidants that help keep the immune system active and efficient.
I drink Lemongrass Herbal Tea. It helps boost the immune system because it is quite rich in vitamin C. Aside from that, this herb also has a lot of antibacterial and antifungal properties that will help fight colds, coughs, and flu.