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 Post subject: Influenza 101: What you need to know
PostPosted: Mon Jan 05, 2009 6:27 pm 
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Influenza 101: What you need to know

Sunday, Oct. 05, 2008

What is the flu? How would scientists make vaccines against it? Why do we need a flu shot every year? And, what can you do to treat or, better yet, try to prevent the flu this winter? Those are just a few of the questions recently fielded by Robert Belshe, director of the Center for Vaccine Development at St. Louis University and a national expert on infectious diseases; Dr. Robert Poirier, clinical chief of emergency medicine at Barnes-Jewish Hospital; and experts at the Centers for Disease Control in Atlanta.

What is influenza?

Influenza (or "the flu") is an infectious disease of birds and mammals caused by the influenza virus. It comes from the Italian word that means "influence."

Depending on its physical makeup, the virus is divided into various types. Those that infect humans are type A, usually the most virulent, type B and type C, which, when it occurs, produces only a mild respiratory infection and is not thought to cause epidemics.

Why can't we simply wipe out the flu virus as we did deadly smallpox?

The influenza virus is a more diabolical critter, Belshe says. Because of its makeup, it can change its appearance about as fast as Clark Kent in a phone booth, leaving the medical world always hustling to catch up.

Think of a virus as a tiny pea. Inside the pea of most viruses is a single strand of genetic material. The flu virus has not one but eight segments, bolstering its ability to do its dirty work.

Those eight genes provide the blueprint for producing various proteins found on the surface of the pea, the most critical of which is hemagglutinin.

Hemagglutinin is the spiked-shaped molecule that attaches to cells in your body to initiate infection. It's also the protein that your body's defense mechanism -- immune system antibodies -- looks for in its search-and-destroy missions.

But just as there are several types of the flu virus, there are also several types of hemagglutinin. Complicating matters further, as the virus replicates in your body, mutations changes the hemagglutinin. These subtle changes may produce a flu strain different enough to evade detection as the disease spreads to other people.

"What that means is antibodies which would attack and kill flu virus of one configuration no longer can kill the new configuration," Belshe said.

As a result, vaccine makers are aiming at a constantly moving target -- a virus that has three major types, several subtypes based on the hemagglutinin and neuraminidase proteins, and ever-evolving new strains.

Why must we be vaccinated every year?

Your body likely still has antibodies to all the flu strains you have encountered throughout your life. But these antibodies only recognize the old strains it has already killed. The annual vaccine exposes your body to the new strains it will likely encounter that winter.

It's sort of like the police (antibodies) being called to shut down a meth house (virus), but the owner keeps changing the house number (hemagglutinin). Someone has to keep updating the police about the new number so they can raid the right house.

But if there are new strains of flu all the time, how do they make a vaccine?

By monitoring flu cases all over the world, scientists make an educated guess which strains will cause the most illness.

Let's say you go to the doctor with what you think is the flu. Your doc will take a throat swab and send it to a laboratory to verify it is the flu and analyze its makeup. Many of these labs send the results on to the CDC, which, in turn, takes part in an international surveillance network run by the World Health Organization (WHO).

"Then, on an annual basis, the WHO convenes a group of experts," said Belshe, who has served on the United States component of the group convened by the Food and Drug Administration. "We look at the worldwide surveillance and make a recommendation on what to put in next year's vaccine based on what's being isolated around the world."

What goes into the vaccine?

It sounds sort of like a Chinese restaurant menu. Scientists pick the two most prevalent strains of the type A virus along with one type B virus. The type A strains are the most prevalent variants of the hemagglutinin-1 and hemagglutinin-3 subtypes.

To manufacture the shot, the viruses are killed, and only the purified hemagglutinin protein is added to the vaccine. An injection will give you precisely 15 micrograms of each of the three strains of hemagglutinin.

"When you inject hemagglutinin into the body, you make antibodies to that hemagglutinin, and that will protect you from flu that carries that exact hemagglutinin," Belshe said.

Patients ages 2-49 may choose to get the FluMist nasal spray vaccine. This consists of 10 million tiny particles of the three live, whole viruses -- in a weakened state.

"It doesn't cause illness, but it is a whole virus," Belshe said. "It does replicate -- meaning, it divides -- to a very low degree and then stimulates antibody production."

What's in this year's vaccine?

As usual, the vaccine has three strains, and, just by the names, you can see how complicated the process is: This year's vaccine contains Type A/Brisbane (Australia)/59/2007/H1, Type A/Brisbane/10/2007/H3 and Type B/Florida/4/2006. The names include where and when the viral strains were first isolated along with the strain number. The H is the hemagglutinin subtype.

How effective will it be in preventing the flu?

As always, experts are keeping their fingers crossed. Because it takes time to grow the virus and make the vaccine, six months to a year elapse before the first doses are given, during which time a new strain may pop up.

"We expect that it will cover the majority of influenza," Belshe said. "But that depends on one, us guessing right, and, two, the virus is not evolving so rapidly that it gets ahead of us. That does happen sometimes, and that happened last year."

But even if the strains do not match exactly, those vaccinated tend to suffer a less severe case of flu if they contract it, Poirier said.

New flu strains seem to start in Asia (for example, the Asian flu of 1957-58 and Hong Kong Flu of 1968-69) and move west. Is that true?

Probably. Why? It's simply a numbers game. As of 2000, nearly 4 billion of the world's 6 billion people live in Asia, so there's a much better chance of new strains of flu developing and taking root there before it spreads.

How can the flu virus cause such serious illness?

Let's say some inconsiderate, flu-ridden office mate sneezes on you. You breathe in his droplets laden with virus, which goes to work attacking your respiratory system

The first target is usually the trachea, or windpipe. The trachea is lined with little fingerlike projections known as cilia. Under normal conditions these cilia beat in rhythm to keep the airway clean. But the flu virus works to destroy the lining of your respiratory tract, causing you to cough.

If you're lucky, you've been vaccinated and your body's immune system will quickly snuff out the viral invader. If not, you may be in for a rough week.

The virus uses its hemagglutinin protein to latch on to your body's cells. Once it's attached, it hijacks your healthy cell and turns it into a virus-replicating plant. Eventually, your cell dies, but the newly produced virus is released to invade more healthy cells, thus continuing the infection process.

Meanwhile, your body's immune system revs up to fight the virus, releasing substances to try to stop this viral replication. Just as a war can leave cities in ruin, this internal battle can cause inflammation and other havoc in your body, such as viral pneumonia and high fever.

Worse, it can open the door to still more opportunistic bugs.

"We begin to see complications after three or four days," Belshe said. "Because the mucosa has been damaged, bacteria can colonize the trachea and cause bronchitis. Or, it can infect the lung to cause bacterial pneumonia. Or it can infect the ear and sinuses so we get sinusitis or otitis media."

If your body is strong enough, it will eventually fight off the infection with rest at home. If not, you may add to the 200,000 annual hospitalizations in the United States.

Who should be vaccinated?

If you're 6 months or older and not a hermit, it's probably a wise idea to be vaccinated. It's particularly crucial for those over 50, those with heart and lung disease -- and all those who live with or care for infants, the elderly and the chronically ill, including day-care providers and health-care professionals.

"The good thing about the vaccine is that if a lot of people get vaccinated, you develop what's called a 'herd immunity,'" Poirier said. "So there's less flu virus going around. The more people who get vaccinated, the less likely you are to catch the flu even if you are not vaccinated because there's less flu being passed around."

Currently, however, only about 30 percent of the population seeks vaccinations. This year, 150 million doses are available, the most ever. Parents should remember that any child under 9 who is vaccinated for the first time will need two doses, a month apart. Everyone else needs only one.

Is there anyone who should not be vaccinated?

In addition to those under 6 months of age, anyone who has an allergy to eggs -- e.g., you get hives when you eat eggs -- should avoid the vaccine because it is cultured in eggs. Also, if you have developed a serious reaction -- such as Guillian-Barré syndrome -- to a previous vaccination, you should skip the vaccine. But these represent only a tiny percent of the population.

Isn't there a chance I can get sick from the shot itself?

No, and if you still don't believe that, consider this little fact: When doctors gave people a shot of pure saline (salt water), 5 percent reported fever, malaise and pain within one week.

"We get the same number when we do that with flu vaccines," Belshe said. "We're confident you cannot get flu from the flu vaccine. But life's events go on, and 5 percent of people do get something within a week. It's just a coincidence."

The only common side effects include soreness at the site of the injection, which is to be expected, low-grade fever and minor aches, which usually last a day or two.

What about the FluMist nasal spray? Unlike the shot, which contains only a protein from the virus, doesn't it have the live, whole virus?

Yes, but the virus in FluMist has been "attenuated" (weakened), so it cannot cause serious illness.

"A small number of people do have a runny nose or a stuffy nose for a day or two," said Belshe, who worked with FluMist extensively during its testing phase.

"It's fairly trivial. A few even have a very mild sore throat. It's so mild that in our clinical trials we didn't see any increased use of Tylenol, for example, with FluMist. So it looks really good when used according to the label."

FluMist, however, is not recommended for pregnant women and people who care for or live with people with severely weakened immune systems, according to the CDC.

How effective is FluMist?

It's apparently more effective than the shot, especially in children, because it stimulates the production of antibodies secreted in the nose, which is where the body is first likely to encounter a flu virus.

"It's a significant advance in our ability to control flu," Belshe said.

I'm over 50, and I don't like shots. Why can't I get FluMist?

Unfortunately, researchers do not know enough about how well FluMist prevents disease in older folks, so it cannot be recommended for those over 49. And, scientists have found that FluMist can cause adverse reactions in children under 2, so infants and toddlers have to be stuck as well.

When should I be vaccinated?

As early in the flu season as is practical because it takes your immune system two to four weeks to build up its defenses (antibodies) to the flu strains in the vaccine, Poirier said. Since 1982, flu season has peaked in February 12 times but it has occurred once as early as November and has been as late as March four times, according to the Centers for Disease Control.

Besides the vaccine, is there anything else I can do to avoid the flu?

Yes, but most aren't very practical. For example, you could take one of the anti-viral drugs approved for use against influenza -- Relenza (zanamivir) and Tamiflu (oseltamivir) -- but you'd have to take it every day during the flu season, which often runs five or six months, and even then it's only 70 percent to 90 percent effective.

You can try avoiding other people, but your boss may frown on you taking a six-month sabbatical every year. Or, you could hope masks come into style in the West.

"It's very common in Asia if you have a cold, you put on a mask," Belshe said. "Or, if you want to avoid a cold, put on a mask. That might work somewhat but none of those things are really, really effective, which is why we really need good vaccines."

Otherwise, follow common-sense advice: Avoid touching your eyes, nose and mouth, avoid close contact with sick people, and cover your nose and mouth when you cough and sneeze.

What about vitamins or other supplements?

Taken in moderation, they won't do any harm, but the consensus seems to be the only effect they'll have is to lighten your wallet.

"Zinc lozenges, vitamin C, echinacea -- all kinds of things are touted for improving flu," Belshe said. "None of them is any good."

"Really, it's whatever that makes you feel the best and lets you get sleep at night because rest and a well-balanced diet is the best treatment," Poirier said.

Will handwashing help?

Handwashing is always a good habit to practice to prevent illness, but it probably isn't as helpful in avoiding the flu. Here's why:

Most viruses are transmitted as "fomites" -- pieces of dry secretion on the hands, desk, etc. When you shake hands or use the keyboard of someone who has a cold, you may pick up some of this person's fomites. Then, if you don't wash your hands, you may infect yourself by touching your fomite-laden fingers to your mouth, hands or eye.

"That's not how flu transmits," Belshe said. "Flu is transmitted by droplets in the air, so that when we talk, when we cough, when we sneeze, we put droplets into the air. Then, if somebody breathes that air, you transmit flu.

"So, because we all have to breathe, it's very difficult to prevent transmission of flu with simple infection-control techniques like handwashing."

How do I know I have the flu?

This can be tricky, because symptoms can mimic those of a regular cold: fever, headache, sore throat, cough, muscle aches and, particularly in children, stomach distress. To be 100 percent certain, you would need a laboratory analysis of your particular virus.

But there are two things that make it more likely you have the flu: One, you know from the news that flu is circulating in your area. Two, the onset of fever and cough has been particularly fast and harsh. (Colds generally take longer to make you feel miserable, and symptoms are often milder and more often include a stuffy or runny nose.) If that's the case, it's 70 percent likely you have the flu.

What should I do if I think I have the flu?

First, consider calling your doctor immediately. If you call at the earliest signs, he can prescribe one of the two anti-viral drugs -- Tamiflu and Relenza -- approved for treating the flu.

"If you take one of these drugs within 48 hours of the onset of the fever, you can shorten the course of disease," Belshe said. "You won't be well, but you'll feel better the next day, you'll reduce complications -- less otitis media, less pneumonia, less hospitalization. But you've got to take the drug quickly because flu replicates so quickly. It does its damage very quickly."

Other than that, it's the same advice you've likely heard for decades: Rest, drink fluids, eat what you can tolerate to maintain energy, and over-the-counter medications to manage symptoms.

"If you have symptoms, don't go to work," Poirier said. "Stay somewhat isolated until you're over the sneezing portion of it so you're not spreading it to others."

Remember, if you don't take care of yourself, flu can open the door to bacterial pneumonia, ear and sinus infections and the worsening of chronic medical conditions, including congestive heart failure. Also, remember not to give aspirin to children and teens with flulike symptoms because it poses the risk of causing Reyes syndrome.

Are there times when emergency care for flu is warranted?

Definitely. Seek help immediately if children are showing any of the following signs: fast or labored breathing, bluish skin color, extreme irritability, not drinking enough liquids, fever with a rash, unresponsiveness, and relapses with high fever and a worse cough.

For adults, it's difficulty breathing, pain or pressure in the chest or abdomen, sudden dizziness, confusion and severe or persistent vomiting.

Am I contagious even before I develop symptoms?

Yes, but flu develops so rapidly that it's only a relatively brief period from the time you're infected to when you start feeling sick.

"People generally start feeling bad within a matter of hours," Belshe said. "They have a fever, and they really feel sick, so they're usually home and bedridden by then."

Adults then usually "shed" (spread) virus for about five days. The more virus you're shedding, the sicker you feel. Children shed virus for about 10 days, and they shed more virus, so they're even more infectious.

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