Should a novel, wholly avian, strain of influenza, and specifically addressed here is H5N1, gain the ability to pass from person to person (H2H) no one, except perhaps the few survivors up until that point will be immune from illness.
By doing everything in my power to avoid getting the annual flu I have robbed my immune system of the very things I will need when facing an influenza pandemic until I qualify for a vaccine, something that I will be waiting a long time for, as I will be standing at the back of a very long line. With this post I hope to specifically address and explain viral immunity, natural or induced, and what it may mean in a time of PanFlu.
Over the last two posts I have introduced heterosubtypic immunity, in plain English: immunity from multiple strains of virus after an immunologic challenge by any strain. An example for influenza could look like this: I get sick with the current circulating strain of H3N2 and recover; I now have antibodies that will make me immune, or at least resistant to not only H3N2, but also the circulating H1N1.
That is the working mechanism of our annual influenza immunizations. Introduce a pathogen (influenza) via vaccine and our bodies develop specialized antibodies and other immune system defenses. However, our annual influenza vaccine (shot) contains only two components of the influenza virus, the HA (hemagglutinin) and NA (neuraminidase), two surface glycoproteins of the virus.
When the body responds to an invading pathogen the immune system deploys various defenses, sending specialized cells to attack, kill, or neutralize the invader. These immunologic defenses attach to things called epitopes on the pathogen. Because the annual flu shot only includes the HA and NA components of the influenza virus our bodies only produce the immunological defenses against those components. Drilling down a bit further, it only develops defenses against those epitopes on these viral segments.
The HA of the influenza virus has five epitopic regions, and one of the reasons we have to get annual vaccines, the other reason is these specific regions of the HA suffer high rates of change, known as single point mutations, where a single nucleotide mutates. This mutation is enough to render it unrecognizable by the defenses the body produced from the vaccine. Instead of a broad based immunity, the annual flu shot produces a very narrowly focused immunity.
Another issue with the annual flu shot is that it is delivered by injection into muscle tissue and the immune response is further restricted to a narrowed subset of the antibodies that would be produced by the body when challenged by a whole virus.
While we develop broad-based, multifaceted immunity after a "case of the flu", strength and length are variable on an individual level, but true in a generalized sense. However, the immunity gained by a flu shot is narrowly deployed and narrowly targeted. For insights into this very narrow specificity and high mutability see Codon bias and frequency-dependent selection on the hemagglutinin epitopes of influenza A virus (here), fair warning though, it is scientifically "dense".
Thanks to FluMist we have a middle-ground choice, that is if we are between the ages of 2 – 49, and healthy, and have no close contacts with individuals with specific health issues. FluMist is comprised of live-attenuated influenza virus that offers a broader immunologic challenge. It gives the body more epitopes to target so the body produces a broader range of antibodies.
One of the major benefits of FluMist is that it is administered intranasally (into the nose as a mist) and one of the immune system components activated is mucosal antibodies, part of the lymphatic system, this same immune component is missing when we get a flu shot.
Another benefit FluMist has over a traditional flu shot is that with the activation of the mucosal portion of the immune system it may be more heterosubtypic, and perhaps greatly so, at least for a short time. This is especially beneficial when the traditional flu shot is not matched to the currently circulating dominant strain of influenza A, as this year's vaccine isn't well matched to A/Brisbane. FluMist, not being as dependent on exact match, will likely confer a greater protection.
In the realm of theoretical:
It may even be that FluMist has a small degree of efficacy when facing a novel pandemic influenza strain. I'm not going to sit here and tell you that it has any chance of conferring 100% protection, and certainly not against a strain as pathogenic as H5N1, but every additional piece of defense we can add to our "pandemic arsenal" the better off we are likely to be. Arming our bodies with as broadly based an immune defense aimed at any influenza A virus the better we are able to survive an infection of H5N1. Nothing in this life is guaranteed, but intranasal vaccination with a live-attenuated virus is an available "mid-point" between suffering a human influenza A virus (which could be lethal in itself) to gain all of the immunological benefits of heterosubtypic immunity and the viral matching specificity of the flu shot.
I would be remiss if I failed to categorically state that while natural infection with influenza A offers the broadest immune response and future protection I in no way recommend anyone refrain from their yearly influenza vaccination in the hopes of gaining that immune storehouse. Even seasonal influenza A can cause serious illness, sometimes with a fatal outcome.
An additional point worth mentioning: Influenza B offers no immunity or mediation against a viral challenge of influenza A. I can get sick with a "B" flu, get well, and two months later be knocked flat on my back with the circulating "A" strain. At least that is my understanding, and the reason that we have both "A" and "B" in our annual vaccination.
Since I have so heavily plugged FluMist I am compelled to state that I have no competing or financial interest with any influenza vaccine (development, manufacturing, distribution, or public relations or any other interest left off the list) FluMist or otherwise. Nor, have I ever taken FluMist, however, I will be asking my family physician for it this year and next, the only two years that I will fall within the "recommended age" range.
And lastly: I am not expert in any of this. I have taken disparate source materials (scientific papers and text books) and agglomerated and distilled "dense scientific or technical gobbeldy-gook" into something that I can only hope is understandable, thorough, useful, and correct. If I have made an error I would appreciate notification of such so that I can correct it!