Live virus vaccines may be administered to birds by incorporation in the drinking water, delivered as a
coarse spray (aerosol), or by intranasal or conjunctival instillation. A live vaccine formulated from a NDV of
low virulence for use in ovo has been licensed for use in the USA. Some mesogenic strains are given by
wing-web intradermal inoculation. Vaccines have been constructed to give optimum results through
application by specific routes.