Deivayanai. V.C , Rajalakshmi Engineering College
Many countries across the globe have huge vaccine-producing factories for making vaccine shots. Certain vaccines are being made where influenza viruses are injected into chicken eggs. These eggs produce a high copy of the viruses. Production workers then extract the viruses from the egg, reduce the virulence or kill them and use these strains to produce vaccines. However, antibodies produced from this method bind not only to the flu virus but also to every virus produced from the egg, thus reducing its specificity. The antibodies produced weren’t binding to the flu viruses, but they readily bind to the biological material in the egg from which it had been grown. Antibodies are normally highly specific to individual pathogens. Thus, this unusual pattern of their activities needed to be addressed to increase their efficiency and targeted protective response.
Egg-based vaccine:
Researchers injected a live virus into the allantoic fluid of an embryonated chicken egg and allowed the virus to replicate inside the egg. Thereafter, they collected the replicated virus with a high copy number, purified them, and killed (or inactivated) them. They used these inactivated viruses (killed viruses) to make the influenza vaccine. This procedure is followed for more than 70 years. Even COVID-19 vaccines are produced in this procedure by few companies.
Virus vaccines produce antibodies against an egg antigen:
Influenza virus cultured in chicken eggs for vaccine generation, often develop mutations during the egg adaptation stage. Seasonal influenza virus vaccines contain an egg-derived glycan (an antigenic decoy), with an egg-binding MAbs reacting with a sulfated N-acetyllactosamine (LacNAc). This egg-grown vaccine binds to an antibody against the egg-derived antigen. It means that the immune response produced will not effectively encounter flu antigen but encounters egg-sugar antibodies instead, which would implicate vaccine effectiveness.
This egg-grown vaccine is not harmful, but not beneficial too, and it affects immunity. It took years for the scientists to identify that the antibodies were linked to egg-sugar antibodies in which they were grown. The antibodies target glycan (sugar molecule). Glycans are a common bio-molecule found in humans, but they are specific sulfur-modified LacNAc found in eggs. They are not expressed in humans.
As a result of this vaccination, human tends to produce antibodies against this sulfur-modified glycan. However, not every individual who was administered the vaccine developed anti-egg antibodies. Thus, there is no clear data on whether the production of anti-egg antibodies reduces the ability to produce anti-influenza antibodies. This also puts vaccine efficiency in question. The vaccines derived from viruses grown in the allantois only tend to produce egg-sugar antibodies while those derived from viruses grown in other parts of chicken cells don’t produce this antibody.
Researchers have concluded that the vaccines produced from the egg cell method are less efficient than other methods. The function of these egg antibodies is unknown. Many people are getting flu vaccines but they don’t develop any adverse side effects. More research should be conducted to know the function of egg antibody or we should study whether this antibody produces immunity against flu and increase the efficiency. Further studies should be conducted on egg antibodies and the reason behind their decreased efficacy. A new method for the production of flu vaccine should be developed to produce a highly effective vaccine.
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Reference:
- Guthmiller, J. J., Utset, H. A., Henry, C., Li, L., Zheng, N. Y., Sun, W., Costa Vieira, M., Zost, S., Huang, M., Hensley, S. E., Cobey, S., Palese, P., & Wilson, P. C. (2021). An Egg-Derived Sulfated N-Acetyllactosamine Glycan Is an Antigenic Decoy of Influenza Virus Vaccines. mBio, e0083821. Advance online publication. https://doi.org/10.1128/mBio.00838-21
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