Background and Aim: One strategy that can be used to stabilize vaccines is to convert them into a dry powder. This can protect the integrity of the active ingredients as well as vaccine antigenicity during manufacture, storage, and transport. This study highlights the potent adjuvant activity of Carbopol^® when used alone to stabilize live-attenuated Newcastle disease virus (NDV) vaccines or when used in a formulation together with skimmed milk. Tolerability and potency of these formulations were compared with those obtained from other local live NDV vaccines produced locally by the Veterinary Serum and Vaccine Research Institute.

Materials and Methods: We evaluated the cellular and humoral immune responses to a locally prepared, live-attenuated LaSota virus vaccine. Vaccine formulations were stabilized with Carbopol^® 940 alone or in combination with skimmed milk.

Results: Our results indicate that the use of Carbopol^® 940 alone to stabilize a live-attenuated LaSota vaccine resulted in enhanced cellular and humoral immunity. The antibody titer was prolonged through the 6th week post-vaccination (5.0 log2). Full (100%) protection was observed in response to challenge with very virulent NDV at day 21 after vaccination; there were no clinical signs or lesions on examination. Addition of Carbopol^® 940 to the live-attenuated vaccine formulation resulted in a more compact, stable, and high-quality lyophilized cake after freeze-dried lyophilization compared with that produced by stabilization with skimmed milk alone.

Conclusion: Our data suggest that Carbopol^® 940 may improve clinical responses to live-attenuated vaccines.

Keywords: Carbopol^® 940, LaSota, lyophilization, Newcastle disease virus, stabilizers, vaccine.