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Demystifying the Flu

21 January 2013
Published in Health
Written by  Kim Schuske

This year, influenza virus has caused 170 hospitalizations, primarily due to H1N1 or swine flu. Last year H3N2 was the primary strain causing disease. But what does this mean and why do we need to get vaccinated every year?

With a single cough from an infected person, flu virus particles are sprayed into the air just waiting for an unsuspecting host to walk by.

“A virus is an organism, and they don’t really have much of a life outside of your body. They’re transmitted from person to person and they infect you and replicate and go onto the next person,” says Robin Bush who studies viral evolution at the University of California, Irvine.

Bush says the flu virus infects us by getting into the respiratory tract and entering into cells in the nose, throat, or lungs. The objective of the flu virus, like all viruses, is to replicate. And they do it by using our cells to make copies of them.  

“It’s really a dirty trick. What it does is, it gets in there and the virus falls apart. It’s little genome segments go into the nucleus where you’re replicating your chromosomes and they get replicated along the way. So you are actually doing all of the work for them.”

Bush adds, “What’s really creepy is that when the little baby viruses come out, they are completely made out of pieces of your body and when you get infected by a flu virus from somebody else, it’s made out of them.”

But for this to work, the virus first has to get into a cell and then the baby viruses have to get out. They are able to do this because they have two special proteins on their membrane surface called H and N.

“The H stands for hemagglutinin and the N stands for neuraminidase,” explains Bush. “These are big long words for little tiny proteins and they stick out through the cell membrane on the virus. The hemagglutinin has a little binding pocket on it that binds to sugars on your lung cells. If there’s no hemagglutinin, you’re not going to be able to infect.”

Neuraminidase helps the new viruses get out of the cells.

“The first ones that we discovered we called H1 and N1 and the second ones we discovered we called H2 and N2 and that’s where those numbers come from,” says Bush.

There are three types of influenza viruses that affect humans. But only two of them, Type A and B, are very common. Type B is the milder of the two. The more severe Type A actually originated in birds. Out of the 17 H’s in birds, only H1, 2, and 3 have been found in humans. Of the 9 N’s, only human forms of N1 and N2 have been found.

This year it’s H3N2 that is the predominant strain in Utah, says Rebecca Ward, with the Utah Department of Health.

“Usually you can expect some hospitalization and some more severity from that particular type,” she says. “But we’re not saying that the severity of illness is anymore critical or severe than it has been in the past. What we’re seeing is just a lot more activity, and it’s coming earlier than expected.”

Ward says that so far Utah has had 389 hospitalized cases of influenza and, unfortunately, four deaths. Luckily, there is a vaccine against flu. The injectable vaccine is made from dead virus and the body reacts to it the same way it would to an actual infection, by producing protective antibodies. Bush says the reason you need to get a flu vaccine every year is because the virus can mutate over time and the antibodies floating around in your body no longer recognize it.

“The three strains that are in the flu vaccine, H1N1, H3N2, and B, are very different from each other, so you need to have all three of them in there. And they’re also all evolving,” says Bush. “And they need to be refreshed or updated every time the hemagglutinins and neuraminidase have evolved enough that the antibodies against the previous vaccine really aren’t working as well anymore.”

This year the Center for Disease Control estimates the flu vaccine is about 60% effective. One reason it’s not better, is that each year scientists have to make an educated guess as to what strains will be circulating in the winter. This year the vaccine matches well to H3N2 and H1N1 strains, but the match to Influenza B isn’t great.

Regardless, since the flu kills between 3,000 and 49,000 people in the U.S. every year, it still makes sense for most people to get vaccinated. Ward says there is plenty of vaccine left in the state, you just may have to search a little harder than usual to find it.

“Some local pharmacies and organizations have run low on their vaccine supplies. Some are in between orders so they may not have some now, but they may have some in a couple of days or another week.”

You can find a vaccine locator at www.immunize-utah.org

Remember, it takes two weeks after the shot until you’re protected, so keep washing those hands.

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