CDC releases preliminary data on 2009 H1N1 vaccine and Guillain-Barre Syndrome
As part of its Morbidity and Mortality Weekly Report (MMWR), the Centers for Disease Control and Prevention (CDC) has released a report titled “Preliminary Results: Surveillance for Guillain-Barré Syndrome After Receipt of Influenza A (H1N1) 2009 Monovalent Vaccine — United States, 2009–2010“. This publication reports on an analysis of preliminary data, the focus of which was to look for any signs of increased risk of GBS rates among individuals receiving the 2009 monovalent H1N1 vaccine in the United States.
Guillain-Barre Syndrome is a rare neurological disorder (affecting about 1.65 and 1.79 in 100,000) in which the body’s immune system attacks part of the peripheral nervous system. On some occasions, it has been identified to be triggered by surgery or vaccination. For example, as has been widely reported, especially by the anti-vaccination crowd, the 1976 influenza A (H1N1) vaccine was associated with a statistically significant increased risk for GBS of over 10 cases per million, and it appears that some vaccines may account for a slight overall increase in GBS risk.
Given the history with the 1976 H1N1 vaccine, the CDC has been closely monitoring the 2009 H1N1 vaccines, through its Emerging Infections Program (EIP) since October 2009. Preliminary results of this analysis show an excess of 0.8 cases of GBS for 1,000,000 vaccinations, similar to the rate for seasonal influenza vaccines. If this holds up when the full review is released some time in the Fall of 2010, it would mean that the 2009 H1N1 vaccine will be associated with an 8% increase over the expected GBS rate of 1 in 100,000.
To put things in perspective, while the H1N1 vaccine may be associated with less than 1 additional case of GBS per million vaccines, the disease it protects from, H1N1 influenza has been associated with 9.7 deaths per million. According to Wikipedia, 80% of GBS patients recover fully, which means that of the 0.8 additional cases per million vaccination, only about 0.16 will have permanent effects (including paralysis and death). To put this further into perspective, if this association holds, we should expect about 16 cases of additional GBS with permanent side effects, for every 100,000,000 vaccinations. At the same time the death rate from influenza A (H1N1) would be at about 970. And if that is not enough perspective, according to this study, the mortality rate, at least for the period 2000-2004 was at 2.58 %, whereas Wikipedia estimates overall mortality rate to be at around 4%. Using the larger number, the 4% from Wikipedia, if the association holds at the same level, we would expect an additional 3.2 vaccine induced GBS deaths versus 970 influenza H1N1 deaths, per 100 million people.