Just get yourselves some tea tree essential oil. It is a powerful anti-microbial. Add a drop to some warm water and gargle twice a day. that will help to kep the flu, strep and other upper respiratory nasties away, plus it's great for dental hygiene. You can also add   a few drops to a water mister and spray indoors where recycled heated air makes germs stick around...
Oh, and be sure to take extra vitamin C EVERY day, and plenty of water. This really helps keep your resistance up.