Systematic Veterinary Virology

LIVE VACCINES

• Live IBD vaccines are produced from fully or partially attenuated strains of virus, known as ‘mild’, ‘intermediate’, or ‘intermediate plus’ (‘hot’), respectively.
• Mild or intermediate vaccines are used in parent chickens to produce a primary response prior to vaccination near to point-of-lay using inactivated vaccine.
• They are susceptible to the effect of maternally derived antibodies so should be administered only after all maternally derived antibodies has waned.
• Application is by means of intramuscular injection, spray or in the drinking water, usually at 8 weeks of age. Intermediate or intermediate plus vaccines are used to protect broiler chickens and commercial layer replacements.
• Some of these vaccines are also used in young parent chickens if there is a high risk of natural infection with virulent IBD. Recently, technology has been developed to deliver live vaccine into eggs during the incubation period.
• Live vaccine virus is blended with IBD antibody and the complex is injected in ovo at 18 days of incubation. The eggs go on to hatch and the vaccine virus is released when the chicks are about 7 days of age.
• In this way, the problem of maternally derived IBD antibody is overcome and the chicks are effectively immunized. Live IBD vaccines are generally regarded as compatible with other avian vaccines.
• However, it is possible that IBD vaccines that cause bursal damage could interfere with the response to other vaccines. Only healthy birds should be vaccinated.