The flu vaccine and GBS

In 1976, a study showed a possible connection between influenza vaccination (the flu shot) and Guillain-Barré Syndrome (GBS). In GBS, the body attacks its own nervous system, causing weakness and paralysis. Most people recover completely over several weeks or months, but some do have permanent problems, and about five percent of people who get GBS die. So, a connection between influenza vaccination and GBS alarmed a lot of people (and rightly so) because we don't want to be giving people GBS when we vaccinate them against the flu. Since 1976, many other studies have looked for a connection between influenza vaccination and GBS.(1)

Only one study has found a connection: it stated that for every one million people vaccinated against the flu, one person "may be at risk of GBS associated with the vaccine." Not "will get GBS," but "may be at risk." And again, no other studies have found any connections between the vaccine and GBS.(1) (See also (3))

What this means is that there may have been a real connection between the vaccine and GBS. Unfortunately, we cannot rule this out absolutely. there is a chance - a very small chance, but a chance - that today's vaccine is somehow connected to GBS.

Does this mean that we shouldn't get vaccinated against influenza? Not necessarily. To decide whether or not to get the vaccine, we need to look at what might happen if we do get the shot and compare it to what might happen if we don't get the shot. We've already looked at the biggest potential negative of the shot. The smaller negatives include things like redness at the injection site, soreness, headache, etc, most no different from the results of placebo treatment. For a small group of people there is an additional negative - if you’re allergic to something in the vaccine, the vaccine can give you an allergic reaction. (This is why they ask you if you’re allergic to eggs, for instance, since eggs are used in the preparation of the vaccine).

There have also been concerns regarding vaccines and autism. This originated with the MMR vaccine. Hilton, Hunt and Petticrew, writing in 2007, note that

The aetiology of autism remains unclear. The suggestion that MMR vaccination may be a cause received wide-spread publicity, although subsequent scientific research has failed to support a link.(2)

On a different note, people who get the vaccine sometimes still get the flu - the vaccine matches what the virus looked like when the vaccine was being made, but the virus looks slightly different now. But the vaccine is still useful, since it primes the immune system, and people who get the flu after getting the vaccine have a milder case of the flu - the illness isn’t as bad. So if you’ve ever gotten the vaccine and later gotten sick with influenza, you would have been even sicker without the vaccine.

Next, we need to look at the positives of getting the vaccine, and then the positives and negatives of not getting the vaccine. Then we’ll be able to make an educated decision on whether or not to get the vaccine.

The benefits of the vaccine are that it provides protection from the flu, as I discuss in this post. Some readers may also be aware of the study that showed that people who received a flu shot are less likely to die - from any cause - over the following year, but I suspect that this is because that those who receive a flu shot are also receiving better all-around medical care - I doubt that the flu shot is a panacea (a cure for all ills). So for our discussion, we’ll focus on the flu, which means we need to talk about what the flu actually can do to us.

Next up: the flu
Also: Why do we need a flu shot every year?

Edited 16 Oct, 4:40 pm Eastern)

SOURCES:
(1) Centers for Disease Control and Prevention, “Seasonal Flu and Guillain-Barré Syndrome (GBS)” at http://www.cdc.gov/flu/about/qa/gbs.htm, on 13 October 2009
(2) Hilton, Hunt and Petticrew, “Autism: a Focus Group study: MMR: marginalised, misrepresented and rejected?” Archives of Disease in Childhood. downloaded 21 March 2008 from adc.bmj.com
(3) World Health Organization, "Influenza vaccines: WHO position paper." downloaded form http://www.who.int/entity/wer/2005/wer8033.pdf on 16 October, 2009

The flu shot, and why we need it every year

So, we've said that the immune system can learn to recognize pathogens, and that a vaccine teaches the immune system to recognize a pathogen (If you don't remember how or why, see the previous post.) If that's the case, why do we need a vaccine for the flu every year?

It turns out that the flu virus is prone to mutation. This year's flu virus doesn't quite look like last year's virus. The change is enough that even if the immune system will recognize last year's virus (either from a vaccine or from getting the actual illness), it probably won't recognize this year's flu virus. So even if we got last year's vaccine, we need this year's to be protected this year.

Next: aren’t there problems with the flu vaccine?

Immune system basics

THE BASICS
The immune system can be divided into two parts: the innate (aka non-specific) part and the acquired (aka specific) part. In most textbooks, the acquired part of the immune system receives the most coverage, but the innate part carries most of the weight, so we'll start there.

The non-specific part of the immune system consists of all of the things that keep pathogens (germs) out of the body. It works similarly to the walls and moat surrounding a castle, which work to keep the enemy soldiers out. The non-specific part of the system includes the skin, and also things like the stomach acid (which dissolves any pathogens that we swallow), and lysozyme (which is found in tears, and breaks down pathogens), and mucus (which traps pathogens that we inhale). Most pathogens don't get past these parts of the non-specific immune system. There are also things like fever, and other changes which help the body fight infections, but also make us feel sick, and these can be considered part of the non-specific system as well.

The specific part of the immune system is only activated if a pathogen does sneak past the non-specific part of the system. It is similar to friendly soldiers within the castle walls, whose job is to recognize, hunt down, and destroy any enemies that manage to get inside of the castle. It consists of B cells and T cells, each of which targets a specific pathogen. (A T cell that can target the bird flu virus, for instance, can only target the bird flu virus. A different T cell is needed for chicken pox virus.) When the specific immune system is activated, it also activates those parts of the non-specific immune system (like the fever, etc discussed above) that make us feel sick. (The fever, etc, also serves as a call to arms for the specific part of the immune system.)

TEACHING THE SPECIFIC PART OF THE IMMUNE SYSTEM
The non-specific immune system is always primed and ready - your skin is always there, keeping pathogens at bay. The specific part of the immune system, when we're born, is naive - it can't really respond to anything very well. But, it does learn. Once the specific immune system meets a pathogen for the first time, it remembers it and responds to it much quicker the next time. This is why if the chicken pox virus sneaks past the non-specific part of the immune system once, we get chicken pox. If the chicken pox virus sneaks past the non-specific part of the immune system a second time, the specific part of the immune system recognizes it and pounces on it, killing it before it can really make us sick. We get the chicken pox once, but not twice. (For those of you familiar with shingles and how it relates to chicken pox, I will be getting to that - don't start writing angry comments just yet)

Wouldn't it be great, though, if we could teach the specific part of the immune system to recognize chicken pox without having to actually get the chicken pox that first time? It turns out that we can. We show the immune system a model of the chicken pox virus, and the system learns what the chicken pox virus looks like from the model. The non-specific immune system activates (so we may feel a bit sick, since merely activating the immune system can make us feel sick), and the specific immune system learns to recognize the chicken pox virus. Then, the first time the actual chicken pox virus sneaks past the non-specific immune system, the specific part of the immune system recognizes the virus from the model and pounces on it before it can make you sick.

What is this model? It's a vaccine. The vaccine looks like the actual pathogen, activates the specific part of the immune system (and may make us feel sick briefly) and teaches it to recognize that pathogen, and when the real pathogen comes around, the immune system pounces on it.

Next: The flu shot, and why we need it every year -->

Edited 20 April 2010