Mutation in Egg-Based Production Renders This Year's Flu Vaccine Less Effective
등록일 2019년 01월 07일 수요일
수정일 2017년 11월 08일 수요일

Photo by: Ananchai Phuengchap via Shutterstock

The season of influenza or flu is around the corner and this year's flu vaccine may be inefficient like the one from last year.According to the Center for Disease Control and Prevention, the effectiveness of the seasonal flu vaccine in 2016 was 42 percent, incapable of protecting people against the infection.

The reason behind the ineffectiveness of the seasonal flu vaccine was due to a mutation that occurred in the influenza A H3N2 vaccine strain.The mutation was a result of an egg-based vaccine manufacturing process used for more than 70 years.

"The majority of influenza vaccine antigens are prepared in chicken eggs.Human vaccine strains grown in eggs often possess adaptive mutations that increase viral attachment to chicken cells," said researchers in a study published in the journal, Proceedings of the National Academy of Sciences.

Still, according to Scott Hensley, author of the new study and an associate professor at the University of Pennsylvania, the best protection against seasonal influenza would be the flu shot available today.

In the development of the yearly flu shot, a vaccine is made based on the virus strains that are expected to spread.Vaccine manufacturers are sent with the selected viral strains to produce their formulations then make them accessible to health care providers before the season begins.CDC estimated the vaccine effectiveness in the 2015-2016 season with 47 percent protection rate, higher than the 19-percent effectiveness of the vaccine in the 2014-2015 season.The overall effectiveness of last season's vaccine was 42 percent but, only 34-percent effective against the H3N2 virus.

However, scientists did not expect that a mutation of the virus in chicken eggs would occur that directly affected the effectiveness of the vaccine.

"The sequences of these viruses are available, and when we did an alignment to see what the sequence of these vaccines was compared to the viruses that were circulating, it became very obvious that there was this mutation," said Hensley.

A research team led by Hensley investigated how the vaccine lost its effectiveness and figured out the effects of the viral mutation.They found that the antibodies extracted in both animals and humans failed to bind and neutralize flu viruses -- a sign of adaptation from the egg-based vaccine flu.

The egg adaptation of the virus is always a difficult problem to resolve.It also forced manufacturers to change the overall manufacturing process to the cell-based production method.Even though the vaccine is far from being adequate, it still prevents people from suffering a severe case of influenza and it can potentially prevent death from the disease.

Vaccine Manufacturing Process for Influenza

There are three manufacturing processes approved by the Food and Drug Administration in producing a vaccine for the influenza virus.

1.Egg-based Flu Vaccines – This is the most common manufacturing process used to produce massive amounts of flu vaccine.It is used to make both the flu shot and the nasal spray to prevent flu infection.The process involves the CDC or another laboratory partner with the World Health Organization Global Influenza Surveillance and Response system providing manufacturers with candidate vaccine viruses.These CVVs are injected by manufacturers to fertilized chicken eggs and incubated for several days so that the virus can replicate.Then, the manufacturers harvest the virus-containing fluid from the chicken eggs.To create the flu shot, the virus is inactivated or killed and its antigen purified.To create the nasal spray, the CVVs are weakened and undergo a process different from the flu shots.

2.Cell-based Flu Vaccines – It involves the WHO to distribute CVVs to manufacturers.The manufacturers inject the CVVs into cultured mammalian cells and leave them for a few days to replicate.They extract the virus-containing fluid from the cells and proceed with the usual process for making flu shots and nasal sprays.

3.Recombinant Flu Vaccines – This process does not require an egg-grown vaccine virus or chicken eggs.The process involves manufacturers separating a certain protein from a naturally occurring recommended vaccine virus called HA protein, a protein that provokes an immune response.The HA protein is then combined with portions of another virus that grows in insect cells.The two compounds are then mixed with insect cells and left for a few days to replicate.The flu HA protein is harvested, purified, and processed for flu shots or nasal sprays.

Additional Information

- The influenza virus has been associated with epidemics and pandemics.In general, the virus caused at least four pandemics of influenza in the 19th century and three in the 20th century.

- The Spanish influenza pandemic caused an estimated 21 million deaths worldwide.

- The first pandemic of influenza in the 21st century happened in 2009 to 2010.

- Pneumonia is the most common complication of influenza.Other known complications include Reye syndrome, heart inflammation, and worsening of chronic bronchitis and other chronic pulmonary diseases.

- Influenza A H3N2 is the predominant cause of hospitalizations with rates from 100 per 100,000 healthy children to 500 per 100,000 children with underlying medical conditions.These children are aged 0 to 4 years old.

Photo by: Kateryna Kon via Shutterstock

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