Guillain Barre Syndrome and Flu Shot

If the flu shot does raise the risk of Guillain-Barre syndrome (GBS), the increase is very small: the US Centers for Disease Control and Prevention (CDC) puts it at about 1 to 2 extra cases per million doses. A person is more likely to develop GBS after having flu than after being vaccinated against it.

What is Guillain-Barre syndrome?

GBS is a rare condition thought to involve the immune system attacking the nerves. It usually causes tingling or numbness in the hands and feet, then muscle weakness, and it can affect breathing and heart rate. It is not contagious or inherited, and the exact cause is unknown.

GBS usually starts a few days or weeks after a respiratory or stomach infection. It occurs in about 1 to 2 of every 100,000 people in the United States each year, or an estimated 3,000 to 6,000 people.

Treatment in hospital usually involves intravenous immunoglobulin or plasma exchange. Most people recover, although recovery can take a long time and some people have lasting problems.

What happened in 1976

The concern about flu vaccines and GBS dates back to the 1976 swine flu vaccination campaign in the United States. That vaccine carried a slightly raised risk of about one additional case of GBS for every 100,000 people vaccinated.

The risk from seasonal flu shots today

Later seasonal flu vaccines have not shown the same risk. CDC says the data vary and are inconsistent from one flu season to another. When an increase has been found, it has been about 1 to 2 extra cases per million doses.

These figures measure slightly different things, but they show the scale: any added risk from a seasonal flu shot is much smaller than the background rate of GBS.

Flu itself can trigger GBS

CDC says GBS is more likely after flu than after vaccination. A 2015 modelling study in CDC's journal Emerging Infectious Diseases noted that earlier studies suggested flu illness may raise the risk of GBS by up to 16 to 18 times, and vaccination by up to 2 times.

The study estimated that, for most people, vaccination slightly lowers the overall risk of GBS because it helps prevent flu. The exception was when flu was uncommon or the vaccine worked poorly in a given season, when vaccination could slightly raise the risk, generally by less than about 1 case per million. This was a simulation based on published estimates, not a direct measurement, and the authors said some of its assumptions are uncertain.

Flu can also cause severe illness and death in its own right. The current medical consensus is that the benefits of vaccination outweigh the risk of GBS.

If you have had GBS before

CDC's vaccine information statement says to tell your vaccination provider if you have ever had GBS, so that they can advise you before you have a flu vaccine.

When to get help

Contact a doctor urgently if you develop tingling or weakness that is spreading, at any time after an infection or a vaccination. Many of these symptoms have other causes, but they should still be checked. Call emergency services if breathing becomes difficult, if one side of your face droops, if you have trouble swallowing or slurred speech, or if you can't lift one or both arms.