Developing Farm-Level Post-vaccination Sero-Monitoring Systems for H5N1 Highly Pathogenic Avian Influenza in an Endemically Infected Country

Abstract

Whilst the serological responses of poultry following vaccination against highly pathogenic avian influenza H5N1 has been extensively investigated under laboratory conditions, there have been fewer studies conducted in the field. This applies particularly to the endemically infected countries routinely practicing vaccination, where the combination of multiple circulating clades and/or the use of vaccines with different seed strains makes the design and interpretation of field studies especially problematic. To address this for the particular situation of layer hens in the small to medium commercial sector in Indonesia, we developed a sampling regime before and after the vaccination given to point-of-lay pullets, and assessed serological response with a panel of test antigens. This confirmed that high titres were induced in those birds vaccinated with locally produced homologous H5N1 vaccines administered two or more times, but in flocks using imported heterologous H5N2 vaccines median titres were significantly lower, and unlikely to provide protection throughout the production cycle, without additional vaccination. Comparing the HI responses against the panel of antigens enabled the detection of the flock's exposure to different vaccine antigens, and made possible the detection of mislabelled vaccine seed strains. Furthermore, we show that test antigens need not be exactly matched to assess sero-protection in well vaccinated birds. Finally our study suggests that the POL vaccination serves as a useful reference point for following cohorts of layers throughout their production cycle, and thus enabling robust vaccination field effectiveness studies.

Keywords: avian influenza vaccines; avian influenza virus subtype H5N1; haemagglutination inhibition test; highly pathogenic avian influenza; poultry vaccination.

Figure 1

The location of the 15 study farms in the districts of Sukabumi and Cianjur in the province of West Java, Indonesia.

Figure 2

The intended sampling regime for the pullets in the study layer flocks, aiming to occur before and after the administration of the POL vaccine. In practice, the vaccination regimes on the farms turned out to be more variable than indicated (Table 1).

Figure 3

Box-plots of individual bird log₂ titer responses against the panel of HI test antigens for the sampling before and after the POL vaccination, grouped according to the country of origin of the POL vaccine: (A) Indonesian vaccines, (B) Chinese vaccines, and (C) Mexican vaccines. Threshold titres for partial (1:2⁴) and full sero-protection (1:2⁵) are indicated with red dotted and red dashed lines respectively.

Figure 4

Dendrogram of the hierarchical cluster analysis of the HI profiles of the 15 sampled farms. For the provenance of the vaccines used for the POL vaccination on each of the farms, refer to Table 2.