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Smallpox vaccine: neurologic adverse events generally mild

Adverse neurologic reactions from smallpox vaccination were generally mild and the rate of specific syndromes did not exceed baseline estimates.

Rare adverse events causally associated with smallpox vaccination include neurologic syndromes such as central nervous system ( CNS ) and peripheral nervous system ( PNS ) complications.

The most common CNS complication after smallpox vaccination is encephalitis ( postvaccinial encephalomyelitis - inflammation of the brain and spinal cord ).
Other infrequent events can include headache, Guillain-Barré syndrome, Bell palsy and myelitis.

James J. Sejvar, of the Centers for Disease Control and Prevention ( CDC ), Atlanta, and colleagues assessed reports of postvaccinial encephalomyelitis and other neurologic adverse events between December 16, 2002, and March 11, 2004, among DHHS and DoD smallpox vaccinees, to clinically characterize them and assess their frequency.

Information on the events was obtained through active case reporting and review of data submitted to the Vaccine Adverse Event Reporting System ( VAERS ) among 665,000 persons vaccinated against smallpox by the Departments of Defense ( n = 590,400 ) and Health and Human Services ( n = 64,600 ) during the 2002-2004 U.S. Smallpox Vaccination Program.

The researchers found that there were 214 neurologic adverse events temporally associated with smallpox vaccination; 111 reports involved DHHS and 103 involved DoD vaccinees.

Fifty-four percent of these events occurred within 1 week of vaccination, and 53 percent were among primary vaccinees.

The most common neurologic adverse event was headache ( 95 cases ), followed by nonserious limb paresthesias ( n = 17 ) or pain ( n = 13 ) and dizziness or vertigo ( n = 13 ).

Serious neurologic adverse events included 13 cases of suspected meningitis, 3 cases of suspected encephalitis or myelitis, 11 cases of Bell palsy, 8 seizures ( including 1 death ), and 3 cases of Guillain-Barré syndrome. Among these 39 events, 27 ( 69 percent ) occurred in primary vaccinees and all but 2 occurred within 12 days of vaccination.

" Our findings identified many milder neurologic adverse events temporally but not necessarily causally associated with smallpox vaccination. They suggest that such events are generally self-limited, non-serious, and not associated with severe morbidity or mortality when screening defers persons with high-risk conditions," the authors write.

" Smallpox vaccine was given to healthy people, which creates a low tolerance for associated risk. Risks associated with vaccines are best identified through population-based assessments. New, possibly less reactogenic smallpox vaccines are currently under development. Continued monitoring for neurologic events is needed to assess the safety of smallpox vaccines and to better characterize the spectrum of neurologic illness associated with them," the researchers conclude.

Source: American Medical Association, 2005