Why vaccination programmes fail to control avian influenza - WUR

Vaccination programs against H9N2 AVI have been ineffective
calendar icon 24 January 2023
clock icon 2 minute read

In some countries, vaccination is the main and most used strategy to control avian influenza (AVI), also known as bird flu. However, most vaccination programs against the H9N2 AVI virus have shown to be ineffective against infection and transmission in the field, although those vaccines were reported to work well in the laboratory in specific pathogen-free (SPF) chicken.

The reason for this, according to a news release from Wageningen University & Research, is that maternal-derived antibodies (MDAs) may interfere with the immune response of chickens to vaccination. Antigen-specific antibodies from mothers are passed to their unborn chicks through the egg, which is called MDAs. The MDAs might be one of the reasons why most vaccination programs against avian influenza have shown to be ineffective in poultry in practice. That is one of the conclusions of a research project into low pathogenic H9N2 avian influenza virus, that is currently prevalent in China, with which Xue Pan obtained his PhD degree at Wageningen University & Research.

Epidemiological investigation

Pan went to several poultry farms in China and did an epidemiological investigation in the field for more than three months. Then he researched three groups of chickens in the lab. In Group 1, all chickens were vaccinated at day one after hatching. The chickens of group 2 got the same vaccine at 21-days-old, according to the company’s vaccination procedure in the field. In Group 3, chickens were not vaccinated and used as control. All groups contained eight commercial broilers and eight SPF chickens. 

"Our results strongly suggest that the maternal-derived antibodies (MDAs) may interfere with the humoral immune responses of chickens to vaccination," said Pan.

More attention to MDA’s

"Our results highlight that we should pay more attention to MDAs interference on influenza virus vaccines in the field, instead of only antigenic distance," said Pan. ‘It is important to create new vaccines to overcome MDA’s interference in the field."

In his research Pan came up with some new vaccines, such as a new adjuvant for conventional H9N2 inactivated vaccine and turkey herpesvirus vector vaccine for improving the vaccines’ efficacy in poultry. And Pan explored some mechanisms that influence the vaccine efficacy.

H9N2 avian influenza

H9N2 avian influenza virus is the most prevalent and harmful low pathogenic avian influenza virus in the world. It not only seriously harms animal husbandry but also poses a huge challenge to public health. Some researchers are concerned that this virus may be a spark to the emergence of the next influenza pandemic, either by directly crossing the species barrier or by donating part of its genes to a pandemic virus.

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