Status and Challenges for Vaccination against Avian H9N2 Influenza Virus in China

Abstract

In China, H9N2 avian influenza virus (AIV) has become widely prevalent in poultry, causing huge economic losses after secondary infection with other pathogens. Importantly, H9N2 AIV continuously infects humans, and its six internal genes frequently reassort with other influenza viruses to generate novel influenza viruses that infect humans, threatening public health. Inactivated whole-virus vaccines have been used to control H9N2 AIV in China for more than 20 years, and they can alleviate clinical symptoms after immunization, greatly reducing economic losses. However, H9N2 AIVs can still be isolated from immunized chickens and have recently become the main epidemic subtype. A more effective vaccine prevention strategy might be able to address the current situation. Herein, we analyze the current status and vaccination strategy against H9N2 AIV and summarize the progress in vaccine development to provide insight for better H9N2 prevention and control.

Oxymatrine Modulation of TLR3 Signaling Pathway: A Dual-Action Mechanism against H9N2 Avian Influenza Virus and Immune Regulation

“…H9N2 AIV mainly targets the respiratory tracts of animals and humans through PMVECs, which form a vascular barrier and play a pivotal role in immune modulation 11 . Despite the virus's low pathogenicity, its rapid mutation rate and e cient transmission, exacerbated by insu cient preventative measures, have rendered conventional vaccine strategies increasingly less effective (Dong et al, 2022). Given this challenge, alternative therapeutic approaches are crucial.…”

Development of an Inactivated Avian Influenza Virus Vaccine against Circulating H9N2 in Chickens and Ducks

“…To date, all of the vaccine strains used in commercial H9N2 AIV vaccines have been isolated from chickens [ 11 ]. Here, a new inactivated vaccine was developed based on a duck-origin H9N2 AIV strain (NJ01), and its protective efficacy was evaluated in both chickens and ducks.…”

“…Vaccination is the main strategy used to control the spread of H9N2 AIV in chicken and duck flocks. The data show that all certified H9-vaccine-related products were inactivated whole-virus vaccines [ 11 ]. However, multiple H9N2 viruses with different antigenicities are prevalent in China, making current vaccination against H9N2 challenging.…”

“…H9N2 has a wide host range, infecting birds, horses, pigs, dogs, ferrets, minks and humans [ 10 ]. In China, H9N2 has been detected in multiple avian species, including chickens, domestic waterfowl and pigeons [ 11 ]. Importantly, human H9N2 infections have been reported globally and have shown an increasing trend in recent years.…”

“…Vaccination has been proven to be an effective way to protect poultry birds from AIV infection. Research and clinical data have shown that inactivated whole-virus H9N2 vaccines can provide protection for immunized chickens by alleviating clinical symptoms [ 11 ]. Nevertheless, antigenic drift frequently occurs on the H9N2 HA molecule.…”