The potential role of an inactivated thermostable vaccine in the control of Newcastle disease in traditionally free-roaming poultry in Central and West Africa.

In spite of the clinical and economic importance of Newcastle disease (ND), vaccination of traditional poultry flocks is not a common practice in Cameroon and other countries in West and Central Africa. This study was designed to demonstrate the importance of vaccination against ND and to propose a sustainable vaccination programme with a LaSota strain of NDV vaccine (Multivax) produced in Cameroon. It consisted of field vaccination trials, determination of a strategic vaccination programme through sero-monitoring and assessing vaccine keeping quality under field conditions. Twelve months monitoring of vaccinated flocks revealed that the epidemic periods of March-April and December-January passed without major incidence in flocks. Mortalities were reduced from above 90% in previous years to 10.8% and 24.6% in two experimental sites respectively. Vaccination antibodies were sustained above protection threshold for about 80 days. A booster administered 35 days after the priming dose did not have any effect on declining serum antibodies. The vaccine remained efficacious in eliciting antibody production for up to 10 weeks after initial use and kept at ambient temperature averaging 34 degrees C. For good protection in a less intense vaccination programme, it would be necessary to administer the vaccine one month to the anticipated month of epidemic, thus requiring at least two campaigns per year.