The influenza virus feels very familiar, who hasn’t had the flu, or knows it comes in the winter and goes in the summer?

But it also seems to throw surprising dangers our way.   In 2009 it was the spring pandemic, in other years it is very mild, and in some years it seems to target unusual populations in upsetting ways, like the 2009 pandemic susceptibility of pregnant women.

And now this year, we are hearing reports about mutations of the influenza virus for 2014-2015, and that this year’s influenza vaccines may not work.

So, what is the story with influenza?  Why is it a different problem every year?  How can a vaccine work one year and not another? Will your child’s influenza immunization work this year?

Here are some answers.  The bottom line is that this year’s influenza immunizations should work very well, and do far more good than not getting one.

The influenza virus, as familiar as it is, is actually unusual, perhaps unique.   Almost all viruses can only infect one species.  Chickenpox only infects humans, and the same is true of measles, colds, stomach flus.  Dogs have their own viruses that do not infect us.

But the influenza virus infects humans in the winter and barnyard animals every spring and summer, every year.  To go from human to cows/horses/pigs requires the virus to change in each direction.  So it has to change to go from humans to pigs, and again from pigs to humans.

As such, influenza is the only common virus that changes every year.

Every virus is a string of genes wrapped in a protein coat. The protein coat contains patterns that allow the virus to open a cell and get their genes inside.   The patterns differ from species to species.

So when the influenza virus enters a human cell, it needs a different protein coat than when it enters a cow cell.

So every spring the protein coat changes to go from human to animal, and every winter it changes again to come back to humans.

It turns out there are just two main types of chemicals on the coat of an influenza virus:  an chemical called H and one called N.  There are a whole bunch of H types, and a whole bunch of N types.

One famous combination is H1N1- the spring pandemic version of the influenza virus in 2009, and still around.

Most vaccines are made against an unchanging virus, so they work forever.  The polio vaccine was created in 1953 and still works fine, since the polio virus has not changed at all.

But since the influenza virus changes every year, returning with a new H and N combination to pick our cell’s locks, the vaccine must change too.

To make an influenza vaccine that will work, every spring the World Health Organization and the CDC actually sample influenza viruses in cows and pigs and horses around the world, to see how the H and N combinations are shifting.  They then take their best guess as to how the influenza virus will change and reappear in humans the upcoming winter.  Tens of millions of doses of influenza shots and mist are made.

Every year, no one knows until the influenza virus returns in the winter, just how the H and N combinations will be, and if the vaccine matches it for real.

In almost every winter there are three to four types of influenza virus that hit humanity, and so the vaccine contains 3-4 strains.

We only give the vaccine that has 4 strains.

The big difference between Flu Mist (the nasal spray) and the flu shot is that the mist has live virus and the shot has dead virus in it.  They are the same viruses, with the same 4 combinations of H and N.

The major result of this difference is that the shot only protects against the four influenza viruses in it.

This year, the combinations are:

A/H1N1

A/H3N2

B/Yamagata/16/88

B/Victoria/2/87

(NOTE- the H and N system fully describes the A strains of influenza, a second group of influenza the B strains use a different system to describe combinations on the protein coat, but it’s the same idea)

So the flu shot will protect against these four influenza viruses, none else.

The flu mist will protect against these four influenza viruses, but since it is live virus, the immunity is stronger and can protect against other combinations.

As with most years, the answer to this has some details.

For both the flu mist and flu shot, the A/H3N2 combination placed in the vaccine turns out not to match the A/H3N2 combination actually infecting people across the US this winter, now.

This is not a failure of the vaccine, missing the exact match is inherent in the process.   Since the influenza virus changes every year when it goes into animals and when it comes back to humans, there is no choice but to guess every spring, and find out every winter how the virus will be.

For the other three combinations, the shot is a 100% match and direct hit.  

The flu mist has a twist this year all its own.  For some reason it’s version of the A/H1N1 is not working in the A/H1N1 circulating across the US this winter.  The good news, though, is that of these four versions and combinations now circulating, there is not much A/H1N1 around as of now, so the flu mist is working very well.

1.  The influenza virus is highly unusual in changing every year.

2.   It changes as it goes to animals in the spring and back to humans every winter.

3.  This means every winter we need a new version of the flu vaccine to contain our best guess version of the flu viruses that will be here in the winter.

4.  All the flu vaccines we offer contain 4 strains.

5.  The flu mist nasal spray is live and therefore gives protection to more than just the 4 strains in it.

6.   The flu shot is dead and so only can protect against the 4 strains in it.

7.   Both the flu mist and flu shot for this winter contain an A/H3N2 combination that does not match the actual A/H3N2 in circulation.

8.   The flu mist’s A/H1N1 does not work well, but there is not much of this A/H1N1 version of influenza virus actually in the community.

9.  Final thought:  influenza viruses cause about a third of all colds and flus in the winter.   Despite some misses on the guesses about what should be in them, you will get fewer colds and flus if you get a flu vaccine- mist or shot.  None of the variance between the guessed virus in the vaccine and the actual virus in circulation present any danger or increased side effect, they just may not work as well.

Dr. Lavin

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