Published: Thu, November 09, 2017
Medical | By Garry George

Why there's no good excuse for not getting the flu shot

Scientists said the research showed the need to improve methods of vaccine production, and to rely less on development of vaccines which use chicken eggs.

The H3N2 influenza viruses evolve rapidly each year and the viruses at the start of a flu season may be well matched to the vaccine, but a few months later they may have drifted and able to evade the vaccine-induced immune response.

Even though the vaccine is not 100 percent effective in preventing flu, it can reduce the severity of flu symptoms. Second, because flu viruses are constantly changing, vaccines are updated annually to keep up with the changing viruses. It was suggested that the A H3N2 virus possessed an adaptive mutation that affected egg-grown vaccines. That's why you should get the flu shot every year.

While it is too soon to say the approach could be successfully used in humans, it appears to be a promising avenue toward a universal flu shot, according to lead researcher Eric Weaver, an assistant professor in the School of Biological Sciences at the University of Nebraska-Lincoln.

The Centers for Disease Control and Prevention (CDC) estimates that past year influenza vaccination prevented approximately 5.1 million influenza illnesses, 2.5 million influenza-associated medical visits and 71,000 influenza-associated hospitalizations.

The goal is to combine the desired HA and NA antigens from the target strain (flu strain 1) with genes from a harmless strain that grows well in an egg (flu strain 2). The eggs are then allowed to incubate, and in turn, this allows the virus to replicate. The vaccine is made from an inactivated virus that can not transmit infection. And this is apparently causing problems with the end product.

It was fortunate that experts correctly predicted the specific viral strain that would dominate the season.

Scientific American explains all the medical details very simply - In 2014, the H3N2 virus began wearing a new molecule on one of its surface proteins.

Flu vaccines work by priming the immune system with purified proteins from the outer layer of killed flu viruses.

"Our experiments suggest that influenza virus antigens grown in systems other than eggs are more likely to elicit protective antibody responses against H3N2 viruses that are now circulating", Hensley said.

Hensley lamented that while the virus could grow in canine or insect cell cultures, only those vaccines catering people with egg allergies undergo such manufacturing process.

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