IMMUNIZATIONS - Medicine for Mountaineering and Other Wilderness Activities - page 57

(VivotifBerna),andarecentlydevelopedinjectablevaccine(TyphimVi®).Theolderheat-
inactivated vaccine is no longer available. The newer vaccines produce fewer side effects.
The live vaccine is administered in four capsules that are taken every other day. The
series should be repeated every five years. Typhim Vi is administered as a single intramus-
cular injection that should be repeated every two years.
Yellow Fever
Yellow fever can be a devastating infection. Approximately 20 percent of such infec-
tions are fatal. Infants and children are at greatest risk. The virus is endemic in the equat-
orial regions of Africa and South America. For travelers, the risk of illness from yellow
fever is probably ten times greater in rural West Africa than in South America ( Figs. 5-3
and 5-4 ) ;these risksvarygreatly according tospecific location andseason. InWest Africa,
themostdangeroustimeofyearisduringthelaterainyandearlydryseasons(JulytoOcto-
ber). Virus transmission is highest during the rainy season (January to March) in Brazil.
Yellow fever has never been recognized in Asia, and its introduction could result in dis-
astrous epidemics because mosquitoes that could spread the virus are abundant. For that
reason, yellow fever immunization is required for travel in many Asian countries, particu-
larly for persons arriving from countries where yellow fever is endemic.
The low incidence of yellow fever among travelers, generally a few hundred reported
casesperyear,hasledtocomplacency.Allfivecasesofyellowfeveramongtravelersfrom
the United States and Europe between 1996 and 2002 were fatal and occurred in unvaccin-
ated travelers.
The attenuated live-virus vaccine is one of the most effective available. A single inocu-
lationprovidesimmunization. Boostersarerequiredeverytenyears,butprolongedpersist-
ence of immunity has been documented and is probably lifelong. Immunizations must be
obtained from a WHO Yellow Fever Vaccination Center, the locations of which can be ob-
tained from local health departments or the CDC website.
The vaccine is prepared from viruses cultured in eggs. Persons allergic to eggs should
not receive the vaccine.
Historically,yellowfevervaccine-associated adverseeventswereseenprimarilyamong
infants and presented as encephalitis. Since 1992, five cases of encephalitis among adult
recipients of yellow fever vaccine have been reported in the United States. In addition, ten
cases of neurologic disease have been reported. Crude estimates of the risk for vaccine-
associated neurologic disease in the United States range from 4 to 6 cases per 1,000,000
doses distributed.