Viruses are hard and stubborn microorganisms which need specific method of treatment. It is different from fungi and bacteria which we deal with them on spot, in case of bacteria and fungi we give the patient the proper treatment that kills the microorganism and cure the case. In case of virus it is relatively different; we deal with virus by giving the healthy person a vaccine and giving the ill person the antiviral drugs.
The vaccines are given early to healthy people regardless if there is a viral infection in the area or not. The vaccine is always a form of killed or attenuated virus, when the body receives the vaccine it starts dealing with it be forming antibodies. The body stores the template for these antibodies in the immune system and especially in thymus gland. If you catch a viral infection then your body will react with the situation by releasing the antibodies specific to this virus. The only problem facing the expansion in producing vaccines is that some viruses are highly mutant, they change their shapes and genetic code with every generation, so if you were injected by a vaccine of a specific strain then you were infected by another one so, the vaccine will not be effective.
The known and popular vaccines are prepared for the sable viruses like polio and diphtheria viruses. These viruses have stability in their genetic code over a long period so even if you were injected with the vaccine while you were a child; it is still effective even when you grow older.
A good example for this case is the influenza vaccine. Since the influenza vaccine mutates nearly every year, the pharmaceutical companies manufacturing influenza vaccines releases a new edition every year to cope with the changes that occur in the virus.
Unlike the vaccines, the antiviral drugs are given to the already infected people not those who are susceptible like the vaccine. This because of the fact the antiviral drug affects the virus life cycle without the production of antibodies. The antiviral drugs differ according to the stage of virus life cycle that they attack. There are entry stage antivirus, uncoating stage antivirus and replication stage antivirus.
Even with the presence of different vaccines and antiviral drugs, there are still some viruses that we do not have a drug to cure. Scientists are doing their best to find a weak point in the lifecycle of these viruses to prepare a suitable drug for them.