The best essential oil for preventing the flu and helping to ease flu symptoms is the Bergamot essential oil.
When you inhale the Bergamot essential oil it has the ability to kill off flu viruses and cold viruses before they have the time to actually effect your body.
If you get the flu or cold virus at a certain time then you should inhale some Bergamot essential oils either with a rag or through a diffuser at least a few days before the flu symptoms usually start.
Another essential oil that is effective at treating the flu and preventing the flu and cold viruses is Eucalyptus essential oil which is antiviral.
Cinnamon leaf essential oil is also antiviral and can sometimes prevent the cold or flu virus from effecting you if you use it before you get infected fully with the flu or cold virus.
You should also up your intake of Vitamin C such as drinking natural orange juice or taking some vitamin c supplements and staying hydrated and getting plenty of rest.