Medical tests show that, like many other viruses, once infected with West Nile, a person acquires a natural immunity to subsequent infection by the virus for the rest of his or her life. This protection, however, may wane with time or in the presence of other health issues that weaken the immune system. There is no evidence that it will help your body fight off other infections during this period when the virus is present. Those who have recovered from West Nile infection experience antibody-mediated immunity against further infection and illness. In fact, research studies have shown that up to 100% of people who recover from clinical infection develop protective antibodies which allow them to avoid future infections. In addition, researchers have also found evidence suggesting that those who have had one exposure to the virus are less likely to contract it again compared to individuals who have never been exposed before. The likelihood of contracting the virus again depends on several factors such as age, prior exposure to other flaviviruses (such as dengue fever), and the strength of the immune response. Individuals who have never been exposed to West Nile but who have strong immune systems still tend to be protected against future exposures. However, those who have previously been exposed to the virus and whose immune responses were not strong enough to combat the first infection may be at risk for a severe outcome if they are exposed to the virus again.