Slight risk of Guillain-Barré syndrome after H1N1 flu vaccination

3D_Influenza_purple_key_pieslice_lrgThe H1N1 influenza pandemic of 2009 was the second pandemic in recent history that resulted from the H1N1 influenza virus, also known as the swine flu. The first one, known as the 1918 flu pandemic, killed over 50 million people, or about 1-3% of the world’s population at the time. The 2009 pandemic, though not as serious as the one in 1918, probably killed over 500 thousand people worldwide. In the United States, the CDC estimated that between 43 and 89 million people were infected with the 2009 H1N1 flu. They also estimated that of those, about 200-400 thousand were hospitalized, and approximately 12,470 died. The only reason the pandemic wasn’t worse was probably as a result of an effective H1N1 vaccine along with a broad effort to vaccinate those at highest risk of complications.

Along with the vaccination program, comprehensive safety surveillance was initiated to monitor for adverse events. This program identified a small increase in Guillain-Barré syndrome following the H1N1 vaccination. In paper published this week, researchers did a meta-analysis of the data from the monitoring program to quantify the level of risk.

Guillain-Barré syndrome is an autoimmune disorder of the peripheral nervous system, where the immune system appears to attack nerves involved in movement, although sometimes it attacks respiration and other functions. Guillain-Barré syndrome is usually preceded by a viral or bacterial infection, such as the flu. It is a serious condition, which often takes several months for full recovery. About 80% of those who contract the disorder recover fully with treatment.

The researchers analyzed 77 cases of Guillain-Barré syndrome that occurred in about 23 million Americans who received the H1N1 vaccine. They found that the incidence rate of Guillain-Barré syndrome was about 2.35 times higher in the 42 days after vaccination. Given that there is a background level of Guillain-Barré syndrome of approximately 1 person in 100,000, the authors determined that there were 1.6 additional cases of the disorder for every 1 million doses of vaccine.

According to Dr. Daniel A Salmon, lead author of the article stated that, “on an individual level, we cannot predict with certainty who will contract influenza, who will have a serious complication or die from the disease, or who will have a very rare but serious adverse event from the vaccine. The safety monitoring programme for influenza A (H1N1) 2009 monovalent inactivated vaccine did not identify any other serious adverse events associated with the vaccine.”

The authors summarize the data, including weighing the small risk versus the vaccine’s benefits:

About 61 million cases of influenza A (H1N1) disease were reported in the USA during the 2009 pandemic, including about 274 000 H1N1-related admissions and about 12 470 deaths. H1N1 vaccines offered substantial protection against medically attended illness. A recent study estimated that the H1N1 vaccination programme prevented 700 000–1 500 000 clinical cases of influenza, 4 000–10 000 admissions, and more than 200–500 deaths. Clinicians, policy makers, and those eligible for vaccination must consider the overall risks and benefits of vaccination, as defined by epidemiological studies, but should be assured that the benefits of influenza A (H1N1) 2009 monovalent inactivated vaccines greatly outweighed the risks.

In other words, the death rate was about 200 for every 1 million individuals that contracted the H1N1 flu. Compare that to the 1.6 Guillain-Barré syndrome occurrences per 1 million individuals who received the vaccine. 

Yes, it is clear that there are some risks (including Guillain-Barré syndrome) to getting a vaccination. In the real world, all medical procedures have some risk associated to them. But in the real world, if those risks include a massive benefit (of preventing death), the logical conclusion is that the Vaccine Saves Lives. 

 

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