IMMUNIZATIONS - Medicine for Mountaineering and Other Wilderness Activities - page 51

elers who are planning to depart in less than six months. The second injection prolongs
immunity.
Another vaccine, Twinrix®, combines hepatitis Aand hepatitis B vaccines. It can be re-
ceived by travelers needing immunization for both infections.
The CDC provides no recommendations for boosters. High levels of immunity after six
to eight years have been documented, and vaccination appears to be effective for twenty
years or more.
Hepatitis B
Hepatitis B is caused by a large, complex DNA virus that is quite different from the
hepatitis A virus and is primarily transmitted by body fluids, particularly blood and semen.
However, contaminated water or food also can transmit the infection. Two safe, effective
vaccinesareavailable:RecombivaxHB®,manufacturedbyMerck,andEngerix-B®,man-
ufactured by GlaxoSmithKline. The usual schedule of primary vaccination for adults con-
sists of three intramuscular doses of vaccine, the second and third at intervals of one and
six months after the first. A third vaccine, Twinrix®, manufactured by GlaxoSmithKline,
is a preparation that contains both hepatitis A and hepatitis B vaccine and can be admin-
istered on the same schedule.
Everyone should obtain hepatitis B vaccination except individuals who have previously
come into contact with this virus, developed natural immunity, and do not need to be vac-
cinated. Such subclinical infections are common in health professionals, individuals living
with persons infected with hepatitis B, injecting drug users, and homosexual men. Testing
for preexisting immunity is not cost effective for others.
Pregnancy is not a contraindication to hepatitis B vaccination.
Hepatitis C, D, and E
Hepatitis D or delta agent is associated with hepatitis B infection and can be prevented
by vaccination against hepatitis B. Although hepatitis C and hepatitis E are common infec-
tions, no vaccines are available.
Influenza
The risk for exposure to influenza during travel depends on the time of year and destin-
ation. In the tropics, influenza can occur throughout the year. In the temperate regions of
the Southern Hemisphere, most influenza occurs from April to September (the winter sea-
son). In temperate climate zones of the Northern and Southern Hemispheres, travelers also
can be exposed to influenza during the summer, especially when traveling as part of large
organized tourist groups or on cruise ships that include persons from areas of the world
where influenza viruses are circulating.