Flu Shot Has Risks, But Still Worth It

H1N1 flu shot risk of Guillain Barre syndrome exists but is very tiny

/ Author:  / Reviewed by: Joseph V. Madia, MD

(RxWiki News) One of the single best ways to avoid getting the flu is to get the flu shot. But some people worry about possible side effects from the shot.

A recent study found that one of the known possible side effects from past shots also existed in the 2009 H1N1 shot. However, the risk of that adverse effect was so tiny that the benefits of the shot still outweighed the risks.

The adverse effect is a condition called Guillain-Barré syndrome. It's a nerve disorder in which a person's immune system attacks the nerves, causing muscle weakness and sometimes partial paralysis.

However, the risk of getting Guillain-Barré from the H1N1 shot was found to be 1.6 out of one million vaccinated people. By contrast, a study last year estimated deaths from the 2009 H1N1 flu to be about 280,000 worldwide.

"Talk to your doctor about the flu vaccine."

The study, led by Daniel A. Salmon, PhD, MPH, of the National Vaccine Program Office within the Office of the Assistant Secretary for Health, used data from six different monitoring systems in the US that track adverse events from vaccines.

These monitoring systems include data gathered from approximately 23 million people who were vaccinated against the 2009 H1N1 influenza in the US.

The researchers looked at all the cases of Guillain-Barré syndrome that occurred among these individuals and when they developed the condition. They found 77 cases that occurred within three months of patients receiving the vaccine.

Guillain-Barré syndrome already affects approximately one out of every 100,000 in the population without the flu shot. Taking this number into account, the researchers found that approximately 1.6 out of every one million people vaccinated could develop Guillain-Barré syndrome following the shot.

In other terms, about three people out of every two million who get the vaccine may develop Guillain-Barré syndrome.

"The modest risk of Guillain-Barré syndrome attributed to vaccination is consistent with previous estimates of the disorder after seasonal influenza vaccination," the authors wrote. "In view of the morbidity and mortality caused by 2009 H1N1 influenza and the effectiveness of the vaccine, clinicians, policy makers and those eligible for vaccination should be assured that the benefits of inactivated pandemic vaccines greatly outweigh the risks."

In other words, despite this small risk of Guillain-Barré syndrome from the flu shot, the risk of getting the flu and even dying from it is higher. Although Guillain-Barré syndrome can take several months to recover from, about 80 percent of all patients who get it have a full recovery.

In the US alone, about 61 million people became infected with H1N1 during 2009, which resulted in about 274,000 hospitalizations and 12,470 deaths. A previous study estimated that H1N1 vaccinations prevented about 700,000 to 1.5 million cases of the H1N1 flu, which meant a reduction in about 4,000 to 10,000 hospital admissions and 200 to 500 deaths.

The study was published March 12 in The Lancet. The authors declared no conflicts of interest.

Reviewed by: 
Review Date: 
March 12, 2013
Last Updated:
March 13, 2013