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FAQs - Fast Facts - What You Need to Know About H1N1 influenza

Posted Sep 03 2009 11:26am
I've been getting a lot of questions from my patients about the H1N1 influenza virus, which was commonly described as the swine flu earlier this year.

Naturally everyone is fearful, particularly about the unknown.

Do I need the vaccine?
Research has shown that the H1N1 virus, which is similar to that of the 1918 Spanish flu pandemic, was around until about 1958. Since then, other influenza types have pushed out this variety. In other words, individuals born before 1958 seem to have some immunity. Those born since then have less protection.

(Note the New England Journal of Medicine article - Historical Perspective — Emergence of Influenza A (H1N1) Viruses - July 16th, 2009, notes that the H1N1 human virus disappeared in 1957 and reappeared again in 1977. The 2009 pandemic H1N1 virus is created by multiple other influenza virus components which is beautifully diagrammed here in the Perspective piece The Persistent Legacy of the 1918 Influenza Virus related to the NEJM article).

CDC also observed that those most impacted by the novel H1N1 virus were those 25 years and younger. Specifically:

The information analyzed by CDC supports the conclusion that novel H1N1 flu has caused greater disease burden on people younger than 25 years of age than older people...


The number of reported cases per 100,000 population was highest among people in the 5 years to 24 years of age group (26.7 per 100,000). This was followed by those in the 0 to 4 years of age group, whose case rate was 22.9 per 100,000 people. The rate declined further to 6.97 people per 100,000 in the 25 years to 49 years of age group. The rate was 3.9 per 100,000 people in the 50 years to 64 years of age group. At 1.3 people per 100,000, the novel H1N1 flu infection rate was lowest in people 65 years and older.

This epidemiological data supports laboratory serology studies that indicate that older people may have pre-existing immunity to the novel H1N1 flu virus. This age distribution is very different from what is normally seen for seasonal flu, where older people are more heavily impacted.

As a result, unlike seasonal influenza the recommended group is young adults, age 24 years old and younger down to 6 months old, caregivers watching children 6 months and younger, as well as those ages 25 to 65 years old who have chronic illnesses and pregnant women. Naturally healthcare workers should all be vaccinated.

Typically seasonal influenza vaccine is given to people 65 years or older unlike the H1N1 vaccine. Also groups at risk very much similar to the list above should be vaccinated. In the past children 6 months to 59 months were recommended to have the vaccination as well. That has expanded to children and teenagers up to 18 years old.

So indications for the seasonal influenza vaccine are very similar to the H1N1 except that people over 65 years old won't need the latter.

Will I get a vaccine?
The information so far is that the H1N1 vaccine will be available in limited numbers because it has been difficult to produce. All influenza vaccines are grown in eggs, this is why before getting vaccinated patients are often asked if they are allergic to eggs. Unlike other influenza strains, this particular one has been very difficult to culture which has been frustrating.

As currently planned, the H1N1 vaccine will be given in two shots. Clinical trials are currently ongoing in Austrialia.

It will not protect against the seasonal influenza virus. So if you need that vaccine, you will need to get it as well.

Either vaccine takes at least 2 to 3 weeks before becoming effective and providing immunity.

For healthcare providers and doctors like myself, this means we will need three shots this year!

How dangerous is the H1N1 virus?
It doesn't appear to be any more dangerous that the typical seasonal influenza virus. However, the typical flu virus does kill about 36,000 Americans annually, so even the "normal" flu virus can be dangerous.

Nevertheless, because it is believed those born after 1958 may not have any natural immunity that the numbers of deaths could be much higher. Organizations are bracing for a busy flu season.

What are the symptoms?
Flu symptoms are classically, high fever, diffuse muscle / body aches, and dry cough. People often remember what time and where they are when symptoms first develop. It can last about 1 week.

It is not a bad cold and symptoms don't usually come on gradually over a period of days.

Complications of the flu can include pneumonia and death.

Can the H1N1 virus be treated?
If you contact your doctor within 24 to 48 hours of having onset of symptoms, then an anti-viral medication known as TAMIFLU can be very helpful. If you think you have the flu, then call your doctor as soon as you are suspicious.

How can I prevent getting the flu?
The typical preventive measures like handwashing and keeping your hands away from the eyes, nose, and mouth are helpful. Handwashing technique using regular soap is fine. The key is washing hands for an adequate period of time like 20 seconds.

Also avoid sick people as well.

If I contract H1N1 earlier in the year, am I immune for the remainder of the year?
Yes. However, it would be far better and presumably less misery if you used the vaccine to have your immune system learn what to watch out for in the future rather than contract the virus.

Note that much like seasonal influenza if you've been exposed that this immunity doesn't carry over to the following year as the strains of influenza virus changes annually. This is the reason that flu vaccines are given annually as the contents of the vaccine need to be changed to match the new viruses, while others like pneumococcal vaccine are given years apart simply as a booster.

Where can I find more information?
Learn more and get updated information at the Centers for Disease Control.

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