What does passaging the Newcastle disease virus through eggs achieve?
The virus is passaged through eggs by the inoculation of the allantoic cavity to increase the quantity of virus. A small amount of the I-2 Newcastle disease virus seed material produces a lot of vaccine. However, the number of passages must be kept as small as possible, or some characteristics of the vaccine may alter. This especially applies to thermostable Newcastle disease vaccines that have been selected for heat-resistance. This property of the virus may be lost during subsequent passaging in embryonated eggs without further heat selection.
