Canadian Immunization Guide
Seventh Edition - 2006

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Part 3
Recommended Immunization

Immunization of Persons with Neurologic Disorders

The Institute of Medicine (IOM) has conducted evidence-based reviews and has rejected any causal associations between the following vaccines and neurological disorders:

• Measles, mumps and rubella (MMR) or thimerosal-containing vaccines and autism spectrum disorders in children;
• influenza vaccine and demyelinating neurological disorders in children aged 6-23 months (the age group studied);
• hepatitis B or influenza vaccines and incident or relapse of multiple sclerosis in adults.

The IOM concluded that the evidence supported a causal relation between the 1976 swine influenza vaccine and Guillain-Barré syndrome (GBS) in adults. The data they reviewed were insufficient to either refute or support any association between GBS and influenza vaccines used after 1976. However, a study by other investigators has estimated the vaccine-associated GBS incidence in adults as one extra case of GBS per million influenza vaccine doses administered. Data on GBS incidence after influenza vaccination in children are not available.

For the purposes of immunization, people with neurologic disorders may be considered according to the following two categories: those with pre-existing neurologic conditions and those in whom the onset of symptoms of a new condition followed immunization.

Pre-existing neurologic conditions

Disorders that usually begin during infancy, such as cerebral palsy, spina bifida, seizure disorder, neuromuscular diseases and inborn errors of metabolism, may have symptom onset before the administration of the vaccines routinely recommended in the first year of life. Other conditions, such as autism spectrum disorders, acute demyelinating encephalomyelitis, transverse myelitis, multiple sclerosis and GBS, often appear later in childhood or adulthood and may occur before or after the administration of the vaccines given to adolescents and adults (e.g., hepatitis B, tetanus, diphtheria and acellular pertussis (Tdap)).

Neurological disorders whose onset clearly precedes immunization are not contraindications to subsequent immunization. People with these disorders are at risk of added morbidity and mortality from vaccine-preventable infections due to Haemophilus influenzae type b, Neisseria meningitidis serogroup C, Streptococcus pneumoniae (vaccine serotypes), pertussis, measles and rubella. Recent studies have demonstrated that children with neurologic conditions are at risk of varicella and influenza infections severe enough to require hospitalization. Consequently, people with pre-existing neurologic disorders should receive all routinely recommended immunizations without delay. In addition, adults and children ≥ 6 months of age with neurologic conditions that compromise clearance of respiratory secretions should receive yearly influenza vaccination. Please refer to the National Advisory Committee on Immunization Statement on Influenza Vaccination available at www.naci.gc.ca for more information.

Neurologic events following immunization

Rarely, neurologic events occur in the 8 weeks following immunization. Because these occur so close in time to the vaccine administration they are said to be "temporally associated". This temporal association alone is not evidence that the vaccine caused the neurologic events. Please refer to the Vaccine Safety chapter for more information. Children who experience hypotonic-hyporesponsive events (HHE), febrile and nonfebrile seizures or prolonged, inconsolable crying after receiving acellular pertussis vaccines or any other vaccine may receive the next dose(s) of vaccines without delay, as these events are not associated with any long-term problems and therefore are not considered contraindications to further immunization. Such events have occurred with equal frequency after either DTaP or DT vaccines, and children have received acellular pertussis vaccines safely after previous HHE episodes.

People with encephalopathy or encephalitis that develops within 7 days after immunization should be investigated. Those who have an alternative etiology for the encephalopathy (e.g., viral infection) or who recover fully by the next scheduled vaccination may be immunized without deferral. People with encephalopathy that persists or who have no alternative etiology should be referred to a specialist for further consultation and may be immunized if their condition is stable and found not to relate to immunization.

Children admitted for investigation of encephalopathy at the 12 participating pediatric tertiary care centres in Canada are captured by the Immunization Monitoring Program ACTive (IMPACT) surveillance system. IMPACT identified four children between 1997 and 2002 with encephalopathy that began within 7 days after immunization with acellular pertussis vaccines. All had concomitant infections or conditions that could have accounted for the encephalopathy. Two of the cases had concomitant influenza A infections, one had a diarrheal illness without any identified pathogen, and the last case was due to hypoglycemia secondary to adrenal insufficiency. Thus, encephalopathy temporally associated with whole cell or acellular pertussis vaccines appears to be very rare in Canada, and these data indicate that an alternative etiology is usually established.

A causal association has not been established between tetanus or currently available influenza vaccines and GBS. However, at the present time it is prudent to withhold tetanus vaccinations from children and adults in whom GBS developed within 8 weeks of a previous tetanus vaccine and to withhold influenza vaccination from children and adults whose GBS developed within 8 weeks of a previous influenza vaccine dose. People who have GBS that developed outside this interval or who have an alternative cause identified (e.g., Campylobacter jejuni infection) may receive subsequent tetanus and influenza vaccinations.

Since the IOM has rejected any causal association between the vaccines identified above and autism spectrum disorders or demyelinating disorders (including multiple sclerosis), children and adults with these disorders may receive further immunization with MMR, hepatitis B and influenza vaccines, as well as other routinely recommended vaccines, without deferral.

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