Guillain-Barré Syndrome & Other Serious Neurological Adverse Events Following Vaccination

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http://www.medscape.com/viewarticle/565691_2Guillain-Barré Syndrome & Other Serious Neurological Adverse Events Following Vaccination

Until now, medical science cannot completely explain the cause of or

mechanisms behind the development of serious neurological diseases,

such as multiple sclerosis (MS), autism, Guillain-Barré syndrome (GBS)

or general encephalopathy. Some of the diseases have definite genetic

risk factors, while others are probably linked to infections. However,

this is not enough to explain the whole picture, especially why some

people develop serious diseases, while others in similar situations are

not affected. As all these diseases do appear from time to time without

obvious reasons, some individuals will necessarily develop such

‘inexplicable’ diseases during the period after vaccination, when

vaccines are administered to large groups of healthy people. This leads

to the question of whether these are causal relationships or just

coinciding events( Table 1 ). Pertussis Vaccine & EncephalopathyThe

first reports of seizures, encephalopathy and other signs of

neurological pathology after vaccination came shortly after whole-cell

pertussis vaccine was taken into general use more than 50 years ago.[7]

As pertussis became rare as a result of vaccination, the focus on

adverse events increased and the vaccine coverage dropped in several

countries, resulting in large pertussis outbreaks and some deaths.[8]

This was the starting point for the really large epidemiological study

trying to determine the relationship between pertussis vaccination and

encephalopathy, the British National Childhood Encephalopathy Study

(NCES). The NCES concluded that the pertussis vaccine might cause

serious neurological effects in approximately one in 100,000 cases.[9]

Further studies found no significantly increased risk of serious acute

neurological illness after the diphtheria, tetanus and pertussis (DTP)

vaccination, but the data were compatible with the concept that

vaccine-induced fever could possibly lead to an illness to which the

child was predisposed, such as febrile convulsions.[10] Despite many large studies, the lack of a causal relationship has never been totally accepted.[11] From a practical point of view, the problem was solved by the introduction of acellular pertussis vaccines.Oral Polio Vaccine: Associations With Poliomyelitis & GBSOral

polio vaccine (OPV) has been the most important tool in the worldwide

campaign attempting to eradicate poliomyelitis. The vaccine is

inexpensive, effective and easy to administer. However, as the vaccine

contains live-attenuated polio virus, there is a risk of

vaccine-associated poliomyelitis (one in 2.4 million doses).[12] Therefore, many countries without endemic polio have switched to an inactivated polio vaccine.[13]

A nationwide OPV vaccination campaign in Finland in 1985 raised the

question of a relationship between OPV and GBS, but in-depth analysis

of the data showed that the increase in GBS occurred before the

vaccination campaign started.[14]Influenza Vaccine & GBSConcerns

about the risk of developing GBS after vaccination have been present

since the mass vaccination with the A/New Jersey/H1N1 vaccine in the

USA in 1976-1977. Nearly the entire adult population was vaccinated,

using more than 35 million doses of the vaccine. A significantly

increased risk of GBS became evident within 6-8 weeks after

vaccination, with the largest percentage of cases occurring 2-3 weeks

after vaccination. The vaccine probably caused approximately one extra

case of GBS per 100,000 immunized persons.[15,16] The risk

was later shown to be associated with the vaccine made from the A/New

Jersey/H1N1 strain. The risk of GBS from other influenza vaccines has

been followed closely in several studies and has been shown to be much

lower, approximately one extra case per million people vaccinated.[17]

According to data from the Vaccine Adverse Event Reporting System

(VAERS) database, the incidence in the USA has fallen significantly

from the 1993-1994 vaccine season (0.17 per 100,000 vaccinees) to the

2002-2003 season (0.04 per 100,000 vaccinees).[18] A

possible explanation of the relationship between the influenza vaccine

and GBS is that the eggs used for vaccine production may have been

contaminated with Campylobacter. Campylobacter infection is a well-known cause of GBS. Better control of Campylobacter

infections in chicken and eggs, especially eggs used for vaccine

production, might explain the contemporary reduced incidence of

influenza vaccine-associated cases of GBS.[18] However, it is impossible to exclude that some influenza vaccines may represent a higher risk of GBS, independent of the Campylobacter

explanation. This is an important point when discussing

mass-vaccination campaigns in a possible new influenza pandemic

situation.MMR Vaccine & Neurological EventsAseptic

meningitis cases after MMR vaccination were reported from several

countries pre-1992. Detailed investigations showed that the cases were

related exclusively to MMR vaccines containing the Urabe mumps strain.

The risk of aseptic meningitis after vaccination with this mumps

vaccine was one in 10,000-15,000 people.[19] After the

withdrawal of vaccines with the Urabe mumps strain, the incidence of

aseptic meningitis has decreased to one in 437,000 doses or less,

according to a recent study from the UK.[19]Other

neurological events after MMR vaccination are rarely seen. GBS has been

reported both after vaccination with the MMR vaccine and the individual

vaccine components,[20] but a large Finish study found no

indication of a causal association between MMR vaccine and other

neurological events other than aseptic meningitis.[21]Hepatitis B Vaccine & MSThe

hepatitis B vaccine has been linked to different serious neurological

syndromes, such as GBS and transverse myelitis, but most of all to the

risk of MS. MS after hepatitis B vaccination has been reported most

commonly in France, possibly because France has implemented large

hepatitis B vaccination campaigns among adolescents and young adults.[22]

Some authors have reported an apparently plausible explanation based on

the fact that hepatitis B vaccine can lead to prolonged surface

antigenemia. The vaccine has, therefore, been associated with the same

kind of autoimmune symptoms or diseases that might be caused by

circulating immune complexes in chronic hepatitis B infection.[23] However, several large case-control studies recently reported no evidence of a link between hepatitis B vaccine and MS.[24,25]