Vero cell-derived inactivated West Nile (WN) vaccine induces protective immunity against lethal WN virus infection in mice and shows a facilitated neutralizing antibody response in mice previously immunized with Japanese encephalitis vaccine.

A novel Vero cell-derived inactivated WN vaccine (WN-VAX) was prepared from virus strain NY99-35262. Two immunizations with WN-VAX induced high levels of neutralizing antibody to WN virus. All immunized mice were protected against challenge with a lethal dose of WN virus. No WN viremia was detected, and the level of WN virus-neutralizing antibody increased rapidly. WN-VAX was then examined for immunogenicity in mice previously immunized with Japanese encephalitis vaccine (JE-VAX). Immunization with WN-VAX induced WN virus-neutralizing antibody in all mice previously immunized with JE-VAX but in only half of the control mice at 10 weeks. These results indicate that WN-VAX induced complete protective immunity against lethal WN infection and that the WN-VAX-induced antibody response is facilitated in JE-VAX-immunized mice. This WN-VAX is thus a candidate WN vaccine for humans.