Guillain-Barré Syndrome (GBS) is thought to be an auto-immune disease of the peripheral nervous system. A patient’s immune system attacks its own Schwann cells. These Schwann cells wrap around peripheral nerves and help speed the transmission of nerve impulses. The attack on the Schwann cells that occurs in GBS causes demyelination, an unwrapping of the Schwann cells. This results in much slower nerve transmission. The result can be a sudden, severe paralysis. With proper supportive care, patients usually make a nearly complete recovery, although there may be residual deficits.
The precise cause of GBS is still under investigation, but a correlation between infections with pathogens like Campylobacter jejuni and GBS have been reported. One hypothesis is that there are small groups of amino acids within the pathogens that also happen to be found on the Schwann cells. The patient’s immune system makes antibodies to fight the pathogen. Unfortunately, these may also turn out to attack the Schwann cells. One way to think of this is as friendly fire during the fog of war.
Although the most evidence has been developed for Campylobacter jejuni infection preceeding GBS, other pathogens may also trigger this “friendly fire”. Among these is influenza (Sivadon‐Tardy, et al. 2009). Since the purpose of the flu vaccine is to stimulate the immune system to respond as if it was being infected, then it would not be surprising if a vaccine itself could cause GBS. However, for most flu vaccines, there is little evidence of such an effect. One exception is the 1976 swine flu vaccine. It is estimated that 1 in 105,000 people needed to be hospitalised as a result of GBS, presumably caused by this vaccine. 25 people, out of 40 million vaccinated, are estimated to have died as a result of vaccine-induced GBS.
Recently, there have been dramatic headlines indicating concern on the part of some neurologists that vaccines to the new H1N1 virus may cause GBS. How serious is this risk? Frankly, we don’t know. The 1976 swine flu and the new H1N1 virus have little in common. So, extrapolating from the vaccine from 1976 and the ones being developed today is risky. However, for the sake of argument, let us say that the risk will be the same, 1 in 105,000 people will need to be hospitalised. Deaths are likely to be lower because supportive care is much better now than in 1976. Let us now consider this risk in comparison with the risk from the pandemic flu virus itself using the leaked CDC case fatality rate numbers. We will also assume a clinical attack rate of 30%.
If you are 25-49 (CFR = 1.5%), your odds of dying of the new flu are 1 in 222.
If you are 50-64 years old (CFR = 3.33%), your odds of dying in the pandemic are 1 in 100.
Since essential workers are primarily in these two age groups, a good case can be made that vaccinating this group.
Pregnant women and children with neurocognitive and neuromuscular disorders also have greatly elevated odds of dying from the new H1N1 virus. Thus, the risk-benefit ratio for vaccinating people in these groups is also likely to be favorable.
The CFR for school age children is 0.22% (according to the leaked CDC document). The risk for this group is 1 in 1,515 that they will die in this pandemic. This risk is substantially less than the other groups, but still much greater than developing GBS after vaccination (assuming 1976 numbers).
We cannot be certain of any of the numbers in this exercise. However, any discussion of the risks and benefits of vaccination should take place in the context of the best quantitative information we have. In my opinion, the risk of the pandemic virus is far greater than the risk of getting GBS from a vaccine. But that risk is not zero. People have a right to know all of these numbers so that they can make informed decisions about whether or not they wish to be vaccinated.