One hundred and fifty (150) unvaccinated 6 weeks old cockerel were divided into six groups of 25 birds each. Pre-vaccination haemagglutination inhibition (HI) mean titers values of 21.4, <21, 21 <21   21 and 21.6 were observed for groups A, B, C, D E and F respectively. Two batches of Newcastle Disease vaccine (NDVI-2) of 50 and 200 doses produced at National Veterinary Research Institute Vom, with EID50 value of 7.7 and 7.6 per dose were administered to groups B and D at 10x (10 times the normal dose) of NDVI-2 via the intra-ocular and intranasal routes. The rest of the groups were administered normal doses of NDVI-2 through the intra-ocular route. Consequently, 40% of the vaccinated birds were randomly selected and sero-monitored twice at 2 and 4 weeks intervals.  No observable ND clinical signs were seen in both groups B and D irrespective of the vaccine over dosage. Post-vaccination (HI) immune profiling of the vaccinated flock revealed steady increase in the HI mean titer value per group, while groups B and D which had 10x the normal dose showed high response in comparison to groups that had NDVI-2 standard dose. HI immune profile results 2 weeks post-vaccination revealed HI mean titer values of 23.0, 24.0, 23.2 24.2 23.6 and 24.4 for groups A, B, C, D, E and F respectively; week 4 post-vaccination haemagglutination inhibition mean titer values of 23.6, 25.4, 23.0 25.7  25.2 and 24.0 for the respective groups. Week 8 HI mean titer values of 22.2, 21.8, 22.4 22.5 23.2 and   21.8 were equally observed. While week 12 HI mean titer values of 22.0, 21.8, 22.0 22.0 21.8 and 21.8 were recorded. Post-vaccination HI mean titer values showed that groups B and D with 10x the normal dose had no observable adverse clinical signs but rather high ND antibody response was observed in groups where overdose of standard NDVI-2 vaccine were administered and evidence of ND antibody depletion was equally observed in all the vaccinated groups irrespective of the dose administrated.

Temperature alterations due to poor cold keeping condition have consistently posed a challenge to vaccines dose EID50 titre value. The sensitivity of Newcastle disease vaccine to temperature variations due to poor cold storage condition in rural settings, led to the development of the NDVI-2 thermostable vaccine, which is known to exhibit a thermostability of 3 hours at 56 °C. In this study, three Newcastle disease vaccines (NDVI-2) with EID50 titre per dose values of log10 EID50 7.7, 7.6 and 6.75 respectively from vaccine production facility at the National Veterinary Research Institute (NVRI), Vom Nigeria, were sent for certification at African Union laboratory at Debre Zeit, Ethiopia under cold condition; using ice packs for cold chain maintenance. Tracking of the vaccine in the course of freight to the certifying laboratory revealed changes in the original transit route by the airline and delay by custom at the receiving country port. Thus, a 12 hours transit freight was delayed for over 7 days before arrival at the certifying laboratory. Though, the EID50 titre per dose values of these vaccines were originally well above recommended EID50 5.5 per dose value by log 2.2, log 2.1 and log 1.25 for NDVI-2 respectively. Comparing these vaccines EID50 values obtained from the certifying laboratory in relation to values initially obtained by the Quality Control Division of the producing Institute (NVRI), revealed  loss of EID50  titre per dose value by log101.2, and log10 0.8 among two of the certified vaccine batches; with one of the certified vaccines retaining its original EID50 titre per dose value. This result attest that NDVI-2 thermostable vaccine produced at NVRI, Vom Nigeria are robust and of high quality. Thus, the findings of this study have further demonstrated that temperature variations, prolonged vaccine transportation under poor cold chain can affect the EID50 per dose value of a wholesome, field fit vaccine irrespective of the vaccine thermostability.