<table class="mainTable"><tbody><tr><td> Flu And You - Part I
by: DemFromCT
Sun Jan 11, 2009 at 13:08:31 PM EST
</td> </tr> <tr> <td> Let's be clear: what makes it a bad flu season is if you (or your family) get it. With that in mind, let's talk about the upcoming flu season, what you need to know about it, and (more next week in Part II) relate it to pandemics and pandemic preparedness and what you need to know about that.
</td> </tr> <tr> <td>How do we know flu season is coming? It comes every year around this time, from Florida to Maine. Flu can hit any time between November and March, but the last few years, February has been the month.

The seasonal flu impact is huge. And just imagine our straining health care system as is... and then add a seasonal flu epidemic (data from CDC.)

Each year, we try to stave off illness by staying as healthy as we can, practice respiratory etiquette and hand washing, and get our annual flu shots. Those flu shots are designed to counter the three strains and sub-types of flu that circulate each year: H1N1 (a remnant of the 1918 flu pandemic), H3N2 (left over from the 1968 flu pandemic) and Influenza B. For that reason, each flu vaccine has three components.
From the CDC website:
Annual influenza vaccination is expected to provide the best protection against those virus strains that are related to the vaccine strains, but limited to no protection may be expected when the vaccine and circulating virus strains are so different as to be from different lineages, as is seen with the two lineages of influenza B viruses.
There are few samples to test because flu season is not in high gear. However, there are already two disappointing things that preliminary lab testing has picked up: - the influenza B component of the vaccine doesn't match one of the two circulating Influenza B viruses this year (there are two Influenza B viruses circulating, but the vaccine well matches the less commonly seen one and not the one that's been most frequently isolated - and remember, there are very few samples overall, so we don't know yet what percentage of each we will see by season's end!)
- the circulating Influenza A H1N1 sub-type is resistant to the commonly used antiviral drug tamiflu (oseltamivir), prompting new recommendations on which drug(s) to use for H1N1 and for Influenza A H3N2 and Influenza B, each of which has a different susceptibility pattern from any of the other circulating flu viruses. The same "only a few samples, so far" caveat applies.
The resistance pattern (but not the Influenza B mismatching) has made it into the press. This is from the Houston Chronicle:
A recently mutated strain of flu that resists the most commonly prescribed treatment has been found in Houston children. Physicians have closely watched the development of this winter's U.S. flu season, because what appears to be the most widely circulating strain, H1N1, has developed resistance to Tamiflu, the leading antiviral drug.
Another leading antiviral drug - Relenza, a powder that must be inhaled - is effective against the strain but is not recommended for children under age 7.
Now, the CDC acknowledges and cautions we don't have a huge sample of virus to conclude anything yet. Things change over the course of the season. But, we generally act with the data we have, and not the data we wish we had (unfortunate that the phrase was co-opted by others, because it's true, sometimes.) Another leading antiviral drug - Relenza, a powder that must be inhaled - is effective against the strain but is not recommended for children under age 7.
So, which strain (A or B) or sub-type (H1N1 or H3N2) is in your community? Ah, now that is a clinical dilemma. Rapid flu tests done in your hospital or doctor's office sometimes distinguish between influenza A and influenza B, but typically don't tell us if it is Influenza A H1N1 sub-type or Influenza A H3N2 sub-type circulating in your area. Those same tests would not inform your doctor if the flu virus was the deadly H5N1, newly arrived from an overseas flight to Jakarta. State labs and the CDC might tell us, but with few samples to rely on, and with the long turn-around time, that's not something we usually know until later into the flu season, long after an individual patient has presented (or in the case of H5N1 or some other novel flu virus, after a large scale problem erupted.) And this year, it seems to matter in regard to how we treat seasonal flu, let alone recognize when we have an unexpected novel virus strain on our hands.
Look at this graph from CDC (click for bigger graph) showing last year's viral pattern over time. Note that H1N1 was a big component early on, but by season's end, H3N2 was predominant:

In any given week, any of the three viruses could have been predominant, and most of the flu viruses are uncharacterized.
So this year, get your flu shot (you, too, health care workers!), and take your doctor's advice about medications, but don't expect 100% flu-proofing. That typically doesn't happen even when the stars are aligned and we have a good year for vaccine matching. The Influenza A viruses seem to match this year's vaccine, but if Influenza B/Victoria lineage (the one that doesn't match the vaccine) is a major player this year, we may have a rough season.
Is there a way to better and faster characterize the sub-types for state and local use? There needs to be. It's one of the many areas of basic research for common diseases that needs to be continued so that we have better diagnostic and treatment tools than we did in 1968 (the year of the last influenza pandemic.) It's one of the many reasons why having a strong CDC is important. It's one of the reasons that pandemic flu preparedness is important - investments in public health infrastructure benefit us for many diseases and conditions, and anything that encourages us to learn more abut flu helps all of us, every year.
Next week we will look at more specifics about how we can improve our lab capability and do a better job of letting clinicians in the community know what they are likely to deal with. For seasonal flu, it's a major problem. In a pandemic, it's critical that we knew exactly what we are dealing with, what resistance patterns are, and whether things are changing with time.
If you want to track whether people are searching the internet about flu in your state, go here. And if you want to see what CDC sees, go here. Any day you want to discuss flu, go here. The slides come from a recent CDC presentation on antiviral resistance which can be downloaded here.
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