Garlic and onions are more potent together than alone. Garlic can reduce blood pressure as it is considered a blood thinner. It has been proven to stop disease (ie remember the plagues of previous centuries?). I've been taking garlic and onions 1-2X per day with lunch/dinner for the past 7 years. It really improved my health, immunity, and aided my blood pressure. If you want to optimize your immunity, garlic and onions (or foods from the same group) should be high on your list. Most people avoid them because of the odor and "questionable" breath they can give you. 2 garlic cloves a day for me + a 1/4-1/2 inch slice of onion. The red onions have more potency but they can give a bit of burn down your throat.
I started taking them religiously in 2009 to combat higher blood pressure. Fwiw I haven't had a bad cold, or any flu for the past 7 years either. For the 10 years prior to that I was catching them multiple times per year along with bronchitis. Those are all gone now. My asthma cleared up as well. Take garlic and onions along with a varied and healthy diet of whole foods, veggies, fruits, etc. Garlic and onions are in my daily salad, any soups, with eggs, with tomato sauces, etc. They actually help to spice up some bland foods like quinoa, beans, etc. My daily salad has garlic and onions, kale/romaine, red cabbage, broccoli, celery, carrots, green/red pepper, apple cider vinegar, tumeric and italian spices. That's super filling even without some fish, chicken or quinoa.
The cancer-fighting benefits are nice too. The only bad? If your blood pressure is super low, maybe it makes it too low. Potent breath is about the only downside. A lot of veggies only have moderate to minimal health benefits. But some others are super foods. Eat the super foods.