O

Odds ratio (OR).

In studies of adverse events following immunization, the odds ratio generally refers to the exposure-odds ratio, which, for a set of case-control data, is the ratio of the odds of exposure among the cases to the odds of exposure among controls (noncases). When the adverse event under study is rare, the odds ratio is a good estimate of the relative risk.

Optic neuritis.

Represents a central demyelinating disease of the optic nerve anterior to the optic chiasm. It can occur as a solitary unexplained monophasic disease or it may be an early sign of multiple sclerosis. See Chapter 3.

P

Paralytic poliomyelitis.

A paralytic disease caused by invasion of the poliovirus into the central nervous system and death of nerve cells in the anterior horn of the spinal cord, the brainstem, and in the motor cortex. The muscle paralysis is usually asymmetrical.

Peripheral mononeuropathy.

See Mononeuropathy.

R

Relative risk (RR).

The ratio of the risk of disease, death, or other outcome among the exposed to the risk among the unexposed. Generally derived from controlled cohort studies or clinical trials. If used in conjunction with adverse events following immunization, when the adverse event under study is rare, the odds ratio is a good estimate of the RR.

Residual seizure disorder.

Recurrent, afebrile seizures; also known as epilepsy.

Reye syndrome.

An acute and occasionally fatal childhood syndrome of encephalopathy and fatty degeneration of the liver marked by rapid development of brain swelling and altered levels of consciousness.

Risk difference.

See attributable risk.

S

Sensorineural deafness.

A form of hearing loss resulting from pathologic changes in the end organ structures within the cochlea or in the neural connections between the cochlea and the cochlear nuclei. See Chapter 3.

Stevens-Johnson syndrome.

See Erythema multiforme.

Serum sickness.

Caused by interaction between antigen and antibody in the circulation with the formation of antigen-antibody complexes in an environment of antigen excess. Symptoms include urticaria, swelling, arthritis, and fever. See Chapter 4.

Subacute sclerosing panencephalitis (SSPE).

A rare form of encephalitis involving both grey and white matter that can affect children and adolescents that is characterized by insidious onset of a progressive cerebral dysfunction occurring over the course of weeks or months. See Chapter 3.

Sudden infant death syndrome (SIDS).

The unexpected and unexplained death of an apparently well, or virtually well, infant. SIDS is the most



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