Aug 17 2009

H1N1 Vaccine and GBS

As most people have probably heard by now, we are in the midst of a pandemic – swine flu or H1N1. This is a strain of the Influenza A virus, which causes a severe respiratory infection. The virus evolves rapidly and each year new strains appear, causing the annual flu season which causes 30,000 deaths in the US and 500,000 world wide.  (The H and N refer to the two main proteins used to classify different strains of the virus – I wrote a more detailed summary here.)

Because the current pandemic is being caused by an H1N1 strain, the same strain that caused the 1918-1919 pandemic that killed millions, world health organizations are understandably concerned and they are tracking it carefully. There are also efforts underway to develop a vaccine. This further raises concerns because of the 1976 H1N1 pandemic – the vaccine given for that strain was linked to cases of Guillain-Barré Syndrome – GBS. Unfortunately, while the likely risk of GBS is much smaller than the risk from the flu itself, this risk has stoked the flames of fear-mongering about vaccines. This somewhat irresponsible article in the Daily Mail is a good example.

GBS

GBS is an autoimmune neurological disorder. It is a monophasic (one time process that gets worse then gets better) post-infectious illness. Essentially, an infection with a virus or bacteria triggers the immune system to have a second inflammatory response against myelin proteins. Myelin is the insulation around nerves – the inflammation inhibits nerve conduction, damages the myelin, and when severe can damage the underlying nerve fiber itself. This results in weakness, numbness, and autonomic dysfunction. The weakness, when very severe, can inhibit breathing resulting in the need for mechanical ventilation. Right now the greatest risk from the disease is the autonomic dysfunction which can cause a severe drop in blood pressure, among other symptoms.

If recognized early and treated properly, most patients with GBS have a short illness – days to weeks – and recover nearly fully. However, severe or untreated cases can result in permanent paralysis and there is a 3-4% death rate. (Although I have treated many cases, I have never seen a death from GBS – not even close. I suspect these cases result from a significant delay in treatment or improper treatment.)

GBS can not only be triggered by the flu or other infections, but also by vaccines used to prevent infections. This is because vaccines are designed to stimulate the immune system, to provoke an immune response – which is what causes GBS. The risk of getting GBS from the flu vaccine is about 1 in a million. This is very reliable data, as we have been using the same basic technology for the flu vaccine for decades and we have reliable statistics on GBS as treatment requires hospitalization. Some cases may be missed if they are very mild (probably rare, but also if a case is too mild to be recognized then who cares) or from misdiagnosis (also probably rare as it is fairly easy to eventually confirm the diagnosis even if it may be difficult initially).

Of note, GBS does not affect the brain (as the Daily Mail incorrectly reported) but only the peripheral nerves. Occasionally the spinal cord may also be affected, but generally speaking GBS is a peripheral disease.

H1N1 Flu Vaccine

As we gear up for the H1N1 flu vaccine there is much fear-mongering among the antivaccinationists, the usual conspiracy theorists and critics (usually competitors) with science-based medicine. The Daily Mail piece, unfortunately, plays into this fear mongering while burying any reasonable responses from scientists deep within the article. The reason the GBS concern is raised is because in 1976 the H1N1 or swine flu vaccine triggered a GBS outbreak, and it is estimated that about 10 in a million recipients came down with GBS. It also turns out that the 1976 pandemic fizzled, and turned out to be very mild.

The flu vaccine uses the same basic technology that has been used for decades, and therefore it is very reliable and the risks are fairly well known. Each year the vaccine has to be tweaked to target the likely strains of Influenza A that will be prominent that year. So the risks from the vaccine may vary slightly as new strains are being targeted, but over the last 30 years since the 1976 episode the risk of GBS has been steady at about 1 in a million – far less than the risk of the flu itself.

Therefore the accusation that the upcoming H1N1 flu vaccine is untested is not a fair or accurate statement. It is highly tested. But it is true that the particular strains targeted will be new. Some charge that therefore vaccinating the public will amount to a large “guinea pig” experiment. This is a naive and misleading statement, however. The fact is that every single medical intervention, every new drug on the market, is in the same situation. Even if we highly test a new drug or treatment in thousands of subjects, it may be marketed to millions. We cannot possibly know the statistical effects on millions of people until it happens. There is therefore nothing different about the H1N1 vaccine from any other mass medical intervention.

If anything, our experience is even greater because we have decades of experience vaccinating millions of people with very similar vaccines.

Even still, it makes sense to track new interventions  – to gather data about what happens when millions are treated. For that reason the British National Health Service has apparently asked neurologists to report new cases of GBS starting this summer. They want to establish a baseline rate of GBS using this reporting system so that if there is a spike of GBS following the H1N1 flu vaccine they will pick it up quickly and can make recommendations about whether or not to continue the vaccine or abort it. This makes sense.

But the Daily Mail is using this precautionary measure to scaremonger about the safety of the vaccine. This is like using the presence of seat-belts in cars to scaremonger about their safety.

Conclusion

The upcoming H1N1 vaccine is simply the regular flu vaccine targeted against the H1N1 proteins to cover the current pandemic strain. Because the pandemic will likely come in two waves, and we are between them right now, this gives us the opportunity to create a vaccine specific for the pandemic strain – rather than guessing, as we do each year for the regular flu season. We have a great deal of information about the safety of this vaccine, but it is always reasonable to track safety going forward. We also have a lot of information about the effectiveness of the flu vaccine – it is very effective. The vaccine itself is very effective, but the actual effectiveness each year varies from 60-80% depending upon whether or not the proper strains were targeted.

The risk of GBS from the flu vaccine has been around 1 in a million – a very rare complication. The risk may not be any higher for the H1N1 vaccine. It is actually not known why the 1976 vaccine had a higher rate of GBS, but it has not been repeated in the last 30 years. Perhaps there is something about H1N1 that increases the risk of GBS, and for this reason monitoring GBS as the vaccine is administered is reasonable. So far, in preliminary tests of thousands of individuals with the new vaccine there has not been any increased risk of GBS, but this process in ongoing.

There are no absolute guarantees in medicine – but the best evidence we have to date strongly suggests that the risk of the H1N1 flu is likely to be much greater than the risk of the vaccine itself. And the usual safety measures and testing are in place – in fact there is heightened safety monitoring. Medicine is a risk vs benefit assessment. But it is easy to fear monger by focusing only on the risk.

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