If you had a vaccine against the flu or fall last winter, you learned the hard way that the vaccine does has not worked as well as usual. Now researchers think they know why :. A mutation that allowed some influenza viruses to beat the vaccine
When we get a vaccine against the flu, our immune cells crank out antibodies that recognize and bind to a known viral protein as the hemagglutinin, which deactivates the virus. However, influenza viruses continually evolve new versions of hemagglutinin that the antibodies do not recognize. This means that the protection provided by the firing of a year generally does not next year, and manufacturers regularly to improve their formulations.
To determine the composition of the vaccine each year, scientists with the World Health Organization (WHO) study the virus strains that are on the loose, and then try to predict which ones will do people sick when the flu season hits. Although patients do not start to get the shots to fall, WHO must deliver its recommendations in February (or September for the southern hemisphere) to allow time for the preparation and delivery of vaccine. "It is very difficult to predict what [viral strains] will be circulated next season," said viral immunologist Scott Hensley of the Wistar Institute in Philadelphia, Pennsylvania. "It is a bit of a guessing game."
last year, WHO has missed the mark :. the vaccine only provides protection of 19%, against less than 60% in other years
Researchers know that some of the problems were. a vaccine against influenza contains a mixture of virus strains, and from 2014 to 2015 shots included a strain of H3N2 influenza virus first isolated in Texas in 2012. WHO scientists think the Texas strain would prevail during the winter, but instead of three other varieties H3N2 jumped. Although the researchers found several mutations of haemagglutinin modifying these H3N2 viruses renegades, they did not know which allowed the virus to evade the vaccine.
to find out, Hensley and his colleagues created a laboratory version of the Texas strain as a comparison standard. The team then developed several varieties of the virus, each of which performs one of the candidates mutations in the haemagglutinin. Next, the researchers mixed the virus in the blood of sheep and ferrets that had recovered from infection with the strain control Texas. This test is a common way to determine how closely the antibodies bind to the virus, an indicator of the amount of protection they offer against infection.
As expected Hensley and colleagues, antibodies in blood samples reacted strongly to the Texas virus control. But as the researchers conclude online today cell reports , the antibodies were a poor match for several viruses that harbored mutations. The transformation with the most powerful effect, known as the F159S name, switch the identity of a single amino acid on top of hemagglutinin.
The scientists saw a similar picture when they tested blood samples from people who had been immunized with the vaccine of 2014 to 2015. The antibodies in the blood switched on the standard virus Texas, but modified virus carrying the mutation F159S triggered a much smaller effect. "They were able to escape or avoid human antibody responses," said Hensley, suggesting that this mutation is largely responsible for the poor performance of last year's vaccine.
For the vaccine this year, the WHO recommended that manufacturers replace the Texas strain with a catch in 2013 in Switzerland. It contains several mutations the researchers tested as F159S. Hensley and colleagues found that sheep antibodies which had recovered from an episode with the Swiss strain reacted strongly to all with mutation of viruses, including those with the mutation F159S.
"This is a solid piece of work," says immunologist Alain Townsend of the University of Oxford in the UK. But this is not the last word on which mutations allowed the virus escape the vaccine, he said. "There are many more [research] can be done with multiple mutations."
In the meantime, the production of this year's vaccine containing the Swiss strain is already underway, and patients should be in line to receive their shots in a few months. Said Gillian Air, a virologist at the University of Oklahoma College of Medicine in Oklahoma City: "We hope the results of this year will be better."
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