Because viruses are geniuses that can change themselves very fast in many different ways making them impossible to target with one molecule (drug).
Because the viruses multiply (replicate) and at the same time they change, so the same vaccine is not gonna be good for the next generation of viruses, they constantly change.
No foods are antiviral. Only fairly strong drugs have antiviral properties.
it is an example of antiviral drugs
Guanine nucleoside analogues, Nucleoside analogues and Antiviral drugs
Exclusive of the antiretroviral agents used in HIV (AIDS) therapy, there are currently only 11 antiviral drugs available, covering four types of virus.
An antiviral drug is a medication used to treat viral infections by either inhibiting the virus from replicating in the body or boosting the body’s immune response to fight off the virus. These drugs are specific to certain viruses and can help reduce symptoms, shorten the duration of the illness, and prevent complications.
Antiviral drugs are the most limited.
As of August 2013, there appears to be new antiviral drugs in the fight against Hepatitus B. According to other reports, there is a potiential antiviral medication that will be able to cure most viruses.
Antivirals are used to treat infections caused by viruses.
Gray, Mary Ann. "Antiviral Medications." Orthopaedic Nursing 15 (November-December 1996): 82.
Just like antibiotics get rid of bacterial infections, antiviral drugs fight against dangerous viruses. A recent example of antiviral drugs is Tamiflu which is used to battle the Swine Flu. For more information, see the below related link.
As a class, the antivirals are not curative, and must be used either prophylactically or early in the development of an infection.
There are antiviral drugs available which have some effect in lessening the symptoms and decreasing the length of herpes outbreaks.