As we ramped up for the H1N1 influenza pandemic last year, one of the worries expressed by the public and by the alternative medicine establishment was Guillain Barre Syndrome (GBS). As explained by neurologist Steven Novella, GBS is a serious auto-immune neurologic disease that causes weakness. It is often preceded by a relatively mild upper respiratory or gastrointestinal illness. In 1976, when a novel swine flu appeared and spread quickly through a military reservation in the U.S. This was a pattern seen in the 1918 pandemic, and the government moved to stem a potential serious pandemic. As it turned out, the pandemic fizzled, but the vaccine was associated with a bump in the incidence of GBS (10 excess cases per 1 million vaccinations).
Since that time, influenza vaccination has been associated with a small increase in GBS, approximately 1 case per million vaccinations. It’s not clear that this relationship is causal, but because of this history, it’s not just the altmed crowd who is interested in this question. The CDC and other agencies have taken an aggressive approach to monitoring the safety of the pandemic influenza vaccine including a possible associations with GBS. The CDC tasked its Emerging Infections Program (EIP) with active surveillance for problems. The EIP sought out cases of GBS through an extensive network of providers and calculated the risks associated with GBS and pandemic flu vaccination.
The preliminary results of this investigation were released this week in my favorite periodical, the Morbidity and Mortality Weekly Report. The CDC found an excess in GBS cases of 0.8 per million vaccinations, similar to previous (post-1976) years. This is a low number, and correlation does not require causation, but it’s important to compare this small risk with the risk of influenza itself. As the CDC summarized:
The 2009 H1N1 vaccine safety profile is similar to that for seasonal influenza vaccines, which have an excellent safety record. Vaccination remains the most effective method to prevent serious illness and death from 2009 H1N1 influenza infection; illness from the 2009 H1N1 influenza virus has been associated with a hospitalization rate of 222 per 1 million and a death rate of 9.7 per 1 million population.
This is good news. In spite of the hype from the altmed industry, we managed to vaccinate a lot of folks and prevent a lot of flu, with very few significant adverse events.