Immunizations For Traveling Abroad

Main Category: Immune System / Vaccines
Also Included In: Tropical Diseases;  Infectious Diseases / Bacteria / Viruses;  Public Health
Article Date: 16 Dec 2006 - 0:00 PDT

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When going abroad, travelers should take time to find the answers to two very important medical questions: what infectious diseases may be in the country they are going to and what immunizations are needed to protect against them? Particularly in the developing world, many diseases seldom seen in the United States are commonplace. Becoming infected with them can have very serious - even fatal - consequences.

"Fortunately, finding information to answer these questions and finding a facility to receive immunizations is relatively easy," says Dr. John Ho, an associate professor of medicine, microbiology and immunology at Weill Cornell Medical College, and an associate attending physician at NewYork-Presbyterian Hospital/Weill Cornell Medical Center. The Centers for Disease Control monitors active diseases in the world as well as emergent local outbreaks, and displays this information on the "travelers' health" section of their Web site.

Travelers who live in, or can visit, the New York area can obtain immunizations at NewYork-Presbyterian/Weill Cornell's International Health Care Service. Established in the 1970s, the Service is actually the oldest travel health facility in the Northeast, and many of its clinicians, such as Dr. Ho, are also researchers who have decades of experience studying infectious disease. The CDC web site also offers information on immunizations and where to obtain them.

Now, let's get down to business. With regard to infectious disease and immunizations, what should you keep in mind when planning a trip abroad?

Childhood Immunizations

Around the mid-1950s, children born in the United States began receiving standardized immunizations against a number of childhood diseases: diphtheria, pertussis, tetanus, polio, measles, mumps and rubella. These immunizations are still given today and for good reason. But, immunizations do not last forever. Even today, these initial immunizations lose their potency in a decade or more and need to be supplemented with booster shots that "challenge cells" to remember the disease they are protecting against.

Here's where the problem lies. Many people don't keep up with the booster shots they need. This doesn't make headlines because the overall incidence of these childhood diseases is fairly low in the U.S. However, send a million American adults overseas, especially to developing countries where the incidence of these diseases is much higher, and they won't be so lucky.

"Even if you never leave the U.S., you should get or renew these immunizations," says Dr. Ho, who cites a mumps outbreak last year in the Midwest as proof. Adults born after 1956 are assumed to have had immunizations and are usually given booster shots. (With some immunizations, a blood test measuring antibodies can determine if the vaccine was ever received.) "But, if uncertain, start from scratch," continues Dr. Ho. "There is little danger in redoing childhood immunizations."

Immunizations for Certain Regions/Countries

Travelers heading to certain regions of the world may also need to be immunized against diseases such as yellow fever, typhoid, Japanese encephalitis and Meningococcal diseases. These diseases are generally not present in North America or Europe, so westerners are not immunized against them nor do they carry any natural immunity. Check the CDC web site for specific instructions on what diseases are where and the recommended immunizations.

Yellow fever and Japanese encephalitis are viral diseases spread between humans, mainly by mosquitoes. Typhoid is spread by eating food or drinking water contaminated with the bacterium Salmonella typhi. And Meningococcal diseases are spread through aerosol contact with the saliva, nose or throat secretions of people carrying the bacterium meningococcus. Transmission usually occurs through talking, sneezing, coughing or kissing.

Meningococcal diseases are less common outside of sub-Saharan Africa, but can be a problem anywhere people live in close proximity to each other, such as in dormitories or military barracks. Several months ago, an outbreak of meningococcal disease occurred in Brooklyn, New York, amongst an extended family living in close quarters.

Seasonal Immunizations

Influenza is a winter viral infection that causes the most severe effects in the elderly, the immune suppressed or those with poor health. For people over the age of 65 (or any adult in poor health), even if not traveling outside the U.S., Dr. Ho recommends getting an influenza vaccine. He also recommends that people over the age of 65 (or any adult in poor health) receive a pneumococcal polysaccharide vaccine (PPV). This vaccine protects against the bacterium Streptococcus pneumoniae, which is most prevalent during winter and can lead to an infection in the lungs (pneumonia), in the covering of the brain (meningitis), or an infection of the blood (bacteremia).

There are a few variables here. Children with compromised immune systems may also want to receive a PPV and influenza vaccine. All children 6 months to 5 years should get an influenza vaccine because they are the group most likely to spread influenza to others. Ask your individual physician for guidance. Also, keep in mind that "winter seasons" vary throughout the world. Sometimes summer in North America is winter elsewhere.

A Word About Live Viruses

Vaccines contain a small amount of the infectious agent (microbe) they are designed to protect against. This virus signals the body to create antibodies and therefore offer protection if the person is ever truly exposed.

Most vaccines use a "dead microbe" which signals the body to create antibodies, but is otherwise ineffective at spreading the illness. However, the vaccines for measles and yellow fever are different. They contain small "live" amounts of the microbe (both viruses in this case) they are designed to protect against. Defending this is rarely a problem for healthy people, but can be problematic for people with compromised immune systems.

As a precaution, those with compromised immune systems should not receive vaccines for measles or yellow fever, or other vaccines containing a "live microbe." And healthy people who receive these vaccinations should avoid contact with immunosuppressed people for the first several weeks after receiving a vaccine. Ask your health-care provider for a more accurate time period. After several weeks, the live microbe is eliminated by the newly acquired immunity, and therefore cannot be passed from the immunized person to others.

Tuberculosis and Malaria

Tuberculosis and malaria continue to be problematic in certain regions of the world. Unfortunately, the current vaccine for tuberculosis is not very effective and is generally not recommended. There is also currently no vaccine for malaria, and daily medication (such as atovaquone/proguanil, doxycycline, or mefloquine) is needed to protect against infection.

Choosing a medication to protect against malaria can be confusing. Not all brands are appropriate for all people, nor do they all protect against every type of malaria. Research what type(s) of malaria is in your host country, and talk with a knowledgeable travel medicine doctor about what medications are appropriate for you and your destination.

Science Briefs is an electronic newsletter published by the Office of Public Affairs that focuses on innovative medical research and patient care at Weill Cornell Medical College.
http://www.med.cornell.edu/science

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