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Your officially unofficial 2015 flu vaccine update

As I mentioned previously, I got the flu vaccine a few days ago. As of today, I do not have a fever, febrile seizures, Epstein-Barr, a reptilian tail growing out of my back, sudden desire to eat durians, or abrupt inclination to watch English Premier League soccer.

But I know I am protected against the flu, and that’s a good thing. I haven’t had the flu since the 1980s, not because I am a superior human being with the most powerful immune system in the world. It’s because I make sure I’m vaccinated against the disease every single year.

Part of the reason I got the flu jab was because my employers demanded it. They needed me healthy when I passed out bribes to physicians and surgeons–oops, I mean when I was visiting top physicians and surgeons to plan clinical trials.

Of course, my employers demanded I wear lead aprons when training physicians on imaging and diagnostic procedures in cardiac cath labs, so maybe they actually cared about me.

But seriously folks, the flu vaccine is important. But there’s always reluctance to get it, so the 2015 flu vaccine update is here to address the issues that may be on your mind.

The 2014 flu vaccine didn’t work.


This is simply not true. Generally, modern flu vaccines are targeted against 3-4 different flu strains, depending on the manufacturer and other issues.

Typically, flu vaccines provide protection against strains, H1N1 (commonly called swine flu), H3N2, and influenza B. In 2014, the seasonal flu vaccine was particularly weak against H3N2, with the CDC estimating that the vaccine effectiveness against H3N2 was less than 30%.

During the Infectious Disease Society of America meeting this week in San Diego, CA, an abstract presented a meta-analysis of 60 past studies of flu vaccine effectiveness (since it’s in abstract form, it hasn’t been peer-reviewed or published, so we’ll have to wait). The study found that the seasonal flu vaccine was just 38% effective against the H3N2 flu virus.

Is that bad? Well, it’s not good.

But let’s remember a few things:



Why the problem with H3N2?


The CDC and other national public health organizations, along with the World Health Organization, meet, usually in February prior to the next flu season, and try to ascertain which flu variants may be the most prevalent in the upcoming year. Because all flu viruses mutate frequently (if those evil pathogens wouldn’t mutate, we’d have lifelong immunity), the CDC, WHO and other groups gather together in a process called a “match” to publish their best ideas on which strains of flu will be most prevalent in the upcoming flu season.

They are not throwing darts at a dartboard, they compile the best evidence which strains have mutated enough and may be pathogenic enough that they should be included in a vaccine. Some mutations aren’t that serious, and prior year’s immunity may prevent infection from flus with small changes.

Remember, there could be dozens of flu variants circulating at the same time. Some are old, and we have immunity. It’s the new ones that cause concern.

The match has to be done far in advance, because flu vaccine manufacturers require substantial lead time to develop, test, manufacture and distribute the vaccine–sometimes a mutation in a flu strain may occur after the match meeting, and the strain isn’t included in the new vaccine.

The H3N2 variant is difficult to predict, because of a small glycoprotein,  hemagglutinin, that is found on the surface of all influenza viruses. Vaccines induce the human immune system to recognize the unique hemagglutinin for each virus to attack the pathogen as an invader.

However, there are frequent mutations to influenza viruses, and the hemagglutinin starts to change in shape and construction, in a process that biologists call “antigenic drift.” Not to be confused with the evolution mechanism called “genetic drift,” antigenic drift is a mechanism for variation in viruses that involves the accumulation of mutations within the genes that code for antibody-binding sites.

Antigenic drift is what makes influenza viruses so nasty. One can have immunity to one strain of flu, but in a few months, the proteins of the virus change enough that the immune system doesn’t recognize it. And then it attacks.

In 2014-15, there was a particularly drastic antigenic drift in the H3N2 virus. In fact, most scientists had figured out that the flu vaccine would not be particularly effective against the “drifted” virus just a few months after the vaccine match was announced.

But the flu virus’s protein can mutate so that it escapes the immune system’s notice. And even though another common flu virus, H1N1, picks up genetic mutations at the same rate as H3N2, H3N2 can change the shape of its hemagglutinin faster. No one knows why.

These mutations add up to what epidemiologists call drift—and last year was an especially drastic case of drift for H3N2. Epidemiologists knew by late spring that the strain they chose for vaccines back in February did not match the one making people sick.

Viruses, like H3N2 influenza, are pathogenic because they evolve fast to avoid the immune system (it’s not a conscience design on the part of viruses, they’re quite simple, but through natural selection). As pathogens, they cause the disease (the flu, in this case), before the immune system kicks in. That’s why we vaccinate, to cause the immune system to kill the virus before it becomes a disease.


So it really is better than nothing


By a lot. A whole bunch.

Some antigenic drifts, through unknown mechanisms, induce pandemics, where thousands and millions of people die. In 1918-1920 flu pandemic was one of the worst of human history–it killed 50-100 million people worldwide. It is believed that the flu variant, H1N1, had mutated in such a way that it caused normal, healthy immune systems to go awry, killing young adults in a higher proportion.

No, there were confounding factors across the world at that time that would have caused the death rate to be particularly high. Modern, 21st century medicine, may have reduced that mortality rate, but the flu caused a “cytokine storm” which probably would lead to sudden death, even with today’s medicine. Ironically, because the cytokine storm requires a healthy immune system, those with malnutrition and chronic diseases probably were spared the worst of the diseases.

So, not matter what the effectiveness of the flu vaccine might be, it’s better than not being protected. Sure, you can believe in one of  the myths about flu vaccines, but that’s not wise.

You might think you have some powerful version of the human immune system (one of the sillier beliefs of people these days), but you don’t, unless you’re vaccinated.

You might think that the flu is easy to deal with, but it’s not. What many people think is the flu is actually a cold, which is mild by comparison.

You might think your children don’t need to worry about the flu. You’d be wrong, very wrong.

Key citations


Michael Simpson
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