Vaccination with inactivated virus against low pathogenic avian influenza subtype H9N2 does not prevent virus transmission in chickens

Hongrui Cui,Mart Cm De Jong,Nancy Beerens,Monique M Van Oers,Qiaoyang Teng,Luzhao Li,Xuesong Li,Qinfang Liu,Zejun Li

doi:10.1016/j.jve.2021.100055

Abstract

H9N2 subtype avian influenza has spread dramatically in China ever since first reported in the 1990s. A national vaccination program for poultry was initiated in 1998. Field isolation data show that the widely used inactivated H9N2 vaccine does not provide effective control of the transmission of this low pathogenic avian influenza (LPAI) virus in poultry. Current research has focused on two reasons: (i) insufficient immune response triggered by the vaccination with the inactivated virus, (ii) the occurrence of escape mutants selected by vaccine-induced immune pressure. However, the lack of effectivity of the inactivated virus vaccine to sufficiently reduce transmission has been noticed. We mimicked the natural infection and transmission process of the H9N2 virus in vaccinated and non-vaccinated chickens. A statistical model was used to estimate the transmission rate parameters among vaccinated chickens, varying in serum hemagglutinin inhibition titers (HIT) and non-vaccinated chickens. We demonstrate, for the first time, that the transmission is not sufficiently reduced by the H9N2 vaccine, even when vaccinated chickens have an IgG serum titer (HIT>23), which is considered protective for vaccination against homologous highly pathogenic avian influenza (HPAI) virus. Our study does, on the other hand, cast new light on virus transmission and immune escape of LPAI H9N2 virus in vaccinated chickens populations, and shows that new mitigation strategies against LPAI viruses in poultry are needed.

Highlights

Low pathogenic avian influenza (LPAI) viruses can still cause severe economic losses in the poultry industry,[1] even though mortality is much lower than that of highly pathogenic avian influenza (HPAI)
The chickens were grouped into high or low hemagglutinin inhibition titers (HIT) groups based on the Hemagglutination Inhibition (HI) assay (Supplementary Table S1) as representa tive for a good or poor vaccination response
As in the field situation, the HIT varied between individuals after vaccination, but vaccination was considered successful for chickens obtaining HIT >21

Summary

Introduction

Low pathogenic avian influenza (LPAI) viruses can still cause severe economic losses in the poultry industry,[1] even though mortality is much lower than that of HPAI. Outbreaks of H9N2 viruses continue to be reported from vaccinated poultry farms.[10] The failure of vaccination might be because of inefficient application, low dose, and low vaccination coverage (especially in the household sector).[11,12] the continuing transmission in combination with the intensive long-term usage of the inactivated virus vaccine may have led to antigenic changes leading to immune escape.[13,14] Due to these possible failures of vaccination in poultry farms, vaccination was suggested as part of an overall integrated control strategy, including continued nation-wide surveillance, farm biosecurity, and DIVA (Differentiating Infected from Vaccinated Ani mals)) strategy.[6,15]

Methods

Results

Discussion

Conclusion