The length of antiviral duration of the virus varies widely among the various viruses, mainly related to the following factors.
1. Local infection and systemic infection in systemic infection, due to extensive exposure of viral antigens and immune system, the disease is often more solid immunity, and a longer duration. Such diseases are mumps, measles, poliomyelitis, Japanese encephalitis and so on. Some viral infections are confined to the local or mucosal surface, and no viremia, these viruses often cause short-term immunity, the host can be infected several times, such as influenza virus and cause common cold rhinovirus and so on.
2. Virus serotype Some viruses are only a single serotype, after the disease get more solid immunity, such as hepatitis A virus, measles virus. And some viruses are particularly sera, such as rhinovirus has more than 700 serotypes, through the establishment of the immune infection on other viruses without cross-immune effect.
3. Antigen variation Some viruses are antigenically unstable, prone to mutations, only transient immunity after infection. For example, influenza A virus surface antigen prone to variation, so that the crowd lost immunity, can cause influenza epidemic, and even global pandemic.