Correlation of haemagglutinin-neuraminidase and fusion protein content with protective antibody response after immunisation with inactivated Newcastle disease vaccines

The correlation between the antigen content of inactivated Newcastle disease (ND) oil emulsion-vaccines and the serological response after immunisation was studied. The haemagglutinin-neuraminidase (HN) and fusion (F) proteins of Newcastle disease virus (NDV) were quantified in 33 inactivated oil-adjuvanted ND vaccines using isopropylmyristate (IPM)-extraction and antigen ELISAs. These commercial vaccines differed in NDV-vaccine strain, the method applied to inactivate the vaccine virus, the vaccine valence and the composition of the oil emulsions. Large differences, up to 100-fold, in the antigen quantities present in different vaccines were found. The NDV-HN content and the NDV-F content of the vaccines both highly correlated with the haemagglutination- inhibiting (HI) antibody titres after immunisation. These correlation's were found over a 10,000-fold range of applied antigen. The antigen content of the oil emulsion-vaccines also highly correlated with virus neutralising antibody titres. The presence of serum HI antibody titres in individual specific pathogens free (SPF)-chickens after immunisation with inactivated ND vaccines was highly indicative for clinical protection against challenge with the virulent NDV-Herts strain. Our results are the first to demonstrate that the protective serological response after immunisation highly correlates with the antigen content of oil-adjuvanted vaccines. (C) 2003 Elsevier Science Ltd. All rights reserved.