Because most cases of typhoid reported in the United States each year are acquired abroad, typhoid vaccine use is targeted for travelers to areas endemic for
Salmonella typhi infection,especially when long-term nonhotel stays are planned. Currently, three typhoid vaccines are available.
The oldest is a heat/phenol-inactivated vaccine, approved for children 6 months to 2 years of age. A two-dose vaccine series confers immunogenicity; the second
inoculation is administered at least 4 weeks after the first dose. Adverse effects include fever and pain with induration and erythema at the injection site. Two newer
vaccines are better tolerated. A recombinant vaccine comprised of purified capsular polysaccharide Vi antigen (Typhim Vi, Pasteur Merieux Connaught) is approved
for individuals 2 years of age or older. It is administered as a single dose and provides approximately 60% to 75% protection for 2 years.
An oral typhoid vaccine, based on a live attenuated strain of Salmonella typhi (Ty21a), is also available (Vivotif Berna vaccine; Swiss Serum and Vaccine Institute,
Berne, Switzerland). The oral vaccine can be used in individuals 6 years of age or older and is administered as a single pill every other day for four doses (days 0, 2,
4, and 6). It provides approximately 60% to 75% protection for 5 years and is well tolerated by most individuals.
Patients should be reminded to keep their vaccine refrigerated between doses. Mild intestinal upset is the most common adverse event. The oral vaccine should be
taken with cool liquid 1 hour before a meal. Immunocompromised individuals and those with chronic inflammatory bowel disease should not receive the oral vaccine,
nor should persons taking antimicrobial agents (antibiotics or antimalarial agents).
Japanese encephalitis (JE) is a mosquito-borne viral infection that exists throughout eastern, southeastern, and southern Asia. In most individuals who become
infected, encephalitis or severe illness does not develop, but when it does, the death rate is 25% and the rate of severe neurologic sequelae is 50%. The disease
occurs in rural environments and is transmitted by a mosquito vector that normally feeds on pigs and birds. Individuals from the United States at highest risk are those
staying longer than 30 days in rural areas (usually in an Asian locale with extensive rice farming and pig husbandry) during the appropriate mosquito season (May
through October in many areas of Asia, but year-round in endemic tropical areas). The overall risk to a traveler is approximately 1 in 1 million; however, this risk may
increase to more than 1 in 20,000 per week for high-risk travel. Risk can be markedly decreased through the use of protective clothing and insect repellents,
especially at dusk.
The JE vaccine (a formalin-inactivated product derived from infected mouse brains) is administered in a three-dose primary series (days 0, 7, and 14 or 30). Booster
inoculation may be administered every 2 years. The most common adverse effects are local, but mild constitutional symptoms may develop in up to 10%. In 0.6% of
recipients, the vaccine can cause urticaria, angioedema, respiratory distress, hypotension, and anaphylaxis. Most allergic reactions can be treated with antihistamines
and corticosteroids; epinephrine and supportive care may be required. Severe reactions usually occur within a day of vaccination but have occurred as long as 2
weeks after administration of any of the three inoculations. Individuals with a history of severe allergic reactions, angioedema, or urticaria are at highest risk for severe
reactions. Individuals should be observed in the office for approximately 30 minutes after administration, and those who receive the vaccine should have access to
medical care for at least 10 days after completion of the vaccine series. Consequently, the vaccine series needs to be started at least 24 days before departure if the
accelerated vaccination course of 0, 7, and 14 days is employed.
Yellow fever is a mosquito-borne hemorrhagic viral illness that can be severe; it is endemic in sub-Saharan Africa and tropical Latin America. The live attenuated virus
vaccine is the only immunization legally required for crossing some international borders. Contraindications include allergy to eggs, immunocompromise, and
pregnancy. Women who receive the vaccine should be advised not to become pregnant for 3 months after vaccination. The vaccine can be administered only through
WHO-approved centers. State departments of public health keeps a list of such sites. Individuals who require yellow fever vaccination should be directed to a yellow
fever vaccination center. Immunized individuals will receive a WHO vaccination certificate. The vaccination record becomes “acceptable” to immigration officers 10
days after the vaccine has been administered. The vaccine is effective for 10 years. Vaccination is recommended for individuals traveling to or living in endemic
areas. Countries may require documentation of yellow fever vaccination, even from individuals who only pass through endemic areas. Countries reporting yellow fever
are posted by the WHO and the CDC; a listing can be accessed at www.cdc.gov.
Most reactions to yellow fever vaccine are local in nature. More rarely, systemic symptoms may develop, usually 5 to 10 days after vaccination. Because of the risk for
vaccine-associated encephalitis, the vaccine should never be administered to children 4 months of age or younger, and rarely to children 4 to 9 months of age. If an
individual is proceeding to an endemic yellow fever area and the vaccine is contraindicated, a yellow fever waiver certificate can be issued from the WHO yellow fever
vaccination center. Immunocompromised individuals and pregnant women who will live long-term in a highly endemic yellow fever area of the world should carefully
weigh the risk of vaccination versus the risks of illness. A desensitization protocol is available for individuals with a history of a severe allergy to eggs. The injectable
cholera vaccine and the yellow fever vaccine should not be administered within 3 weeks of each other. The effectiveness of the yellow fever vaccine is not affected by
the administration of immunoglobulin.
The risk of cholera for routine travelers is extremely low; the food and water that transmit Vibrio cholerae usually have to be heavily and grossly contaminated, and
simple food and water precautions effectively eliminate any real risk of contracting cholera. Individuals who die of cholera die of dehydration, not of the infection itself.
In the extremely unlikely event that a traveler does contract cholera, simple rehydration therapy will prevent death. The only cholera vaccine currently available in the
United States is an injectable phenol-killed Vibrio cholerae vaccine. The vaccine is minimally protective and is associated with a very high rate of adverse events.
These factors combine to limit the utility of cholera vaccination in the United States. The WHO has removed the cholera vaccine from its list of vaccines for travelers.
During outbreaks, local governments may require documentation of vaccination against cholera fromsome travelers. If used, the vaccine is administered in two doses
at least 1 week apart and, preferably, 1 month or more apart. Boosters are required every 6 months. Oral vaccines are available for use outside the United States.
In the United States, the smallpox vaccine is currently administered only to certain laboratory researchers and to individuals in the Armed Services. The vaccine
contains a live attenuated virus and can result in disseminated vaccinia in individuals who are immunocompromised. Because of the risk for the reemergence of
smallpox resulting from a bioterrorist act, the vaccine is once again being formulated.
Vaccines exist for a number of other infections, including anthrax, typhus, and plague. Vaccines are usually administered to individuals at high risk for these disorders
(usually through employment-related exposures) or to military personnel.
(Primary Care Medicine: Office Evaluation and Management of the Adult 4th edition )
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