In a review of data covering 13 years and millions of
patients, researchers found no evidence of a link between being vaccinated
against tetanus, hepatitis, pneumonia or flu, and developing the nerve-degenerating
"The take home message is vaccines are not causing
Guillain-Barr? Syndrome at a rate, if at all, that would possibly make the
benefits of vaccination not worthwhile," wrote Dr Daniel Salmon, of the
Institute for Vaccine Safety at Johns Hopkins University, who was not part of
the study, in an email to Reuters Health. Guillain-Barr? syndrome (GBS) is a
rare condition that affects one person out of every 100 000 and can lead to
paralysis, which is usually temporary.
GBS is considered an autoimmune response, in which a
person's own immune cells attack the protective coating on nerve fibres. Most
cases follow a bacterial or viral infection, and develop over the course of
days or weeks.
A vaccine to prevent
In 1976, a vaccine created to protect against an epidemic of
swine flu that never materialised was linked to an increased risk of GBS in
people who got the shot. Ever since, researchers have been looking at whether
flu vaccines or any other vaccines might be associated with heightened
risk."There's definitely a connection in people's minds that vaccines
cause this syndrome. But if you look at the (medical) literature, that doesn't
bear out," said Dr Roger Baxter, the new study's lead author and
co-director of the Vaccine Study Center at Kaiser Permanente in Oakland,
Most studies have found no link between Guillain-Barr? and
vaccines, while a handful have shown a very small increase in risk among people
who received specific flu vaccines. That includes a one in one million chance
of GBS among older people who got the 2009 shot against the new H1N1 flu
strain. Because the disorder is so rare, it's extremely difficult to determine
whether a particular vaccine could have caused increases in cases, Baxter said.
linked to H1N1 flu
So he and his colleagues looked to the large dataset of
hospitalisation records at Kaiser Permanente Northern California to see if they
could spot a connection. From 1995 to 2006, there were 415 cases of
Guillain-Barr?.This was out of nearly 33 million person-years, a number that
reflects both the number of people tracked and how long they were followed. For
instance, 3.3 million people tracked for 10 years would represent 33 million
Among the 415 GBS cases, Baxter's team found, two-thirds had
a documented gastrointestinal or respiratory infection in the weeks before
developing GBS. Just 25 people had received a vaccine of any kind within six
weeks of the onset of GBS. Eighteen had flu shots, two got pneumonia vaccines,
three had tetanus shots and three got hepatitis vaccines.
Baxter, who has received research grants from numerous
vaccine manufacturers, said these numbers were no higher than
expected."The bottom line is we think vaccines are very safe for this
outcome, that they do not result in GBS, and if they do, it's so rare it's
nothing to be worried about," he told Reuters Health.
Seasonal pattern in
the records more in winter
The researchers also noted a seasonal pattern in the
records, with GBS cases about 50% more common in winter. That result also
agrees with prior research. It's thought that seasonality in the appearance of
Guillain-Barr? cases may mirror seasonal rates of infections, especially with
flu and other respiratory illnesses.
One recent French
study found, for instance, that people who developed GBS were twice as likely
to have had the flu or to have taken flu medication in the two months before
the disorder set in. Dr Edward Belongia, director of the Epidemiology Research
Center at Marshfield Clinic Research Foundation in Marshfield, Wisconsin, said
it's important that studies like the current one monitor vaccines once they are
on the market to spot possible safety concerns.
"It did happen in 1976, so we know it can happen,"
Belongia said. Since then, however, "I think the evidence is clear, and
this study just provides additional reassurance that vaccines are very safe
with regard to GBS," he added.