Immunization Issues

Typhoid Fever

Updated: September 1, 2004

Typhoid fever is a serious disease caused by the bacterium called Salmonella enterica serotype Typhi (S. Typhi).1

The infection is spread from person-to-person by the fecal-oral route. That means that people get typhoid from food or water contaminated with the feces of infected people.

Typhoid symptoms include high fever, weakness, stomach pains, headache, loss of appetite, and sometimes a rash. Infection can spread to many other places in the body (such as bones) and can cause rupture of the intestine. It kills up to 30% of people who get it, if they are not treated.

Some people who become infected with S. Typhi become chronic carriers—they have no symptoms but have S. Typhi in their feces. Chronic carriers can spread S. Typhi to other people especially when handling food.

Antibiotic therapy reduces deaths and complications caused by typhoid fever. However, in recent years S. Typhi has acquired resistance to many of the antibiotics most widely available for its treatment. Typhoid vaccine can reduce the risk of illness in those who are exposed to S. Typhi.

According to the World Health Organization, 16 million people get typhoid every year around the world and about 600,000 die from the disease.2

Typhoid is not common in the United States. Although 356 cases of typhoid fever were reported in the US in 2003,3 most of these infections are acquired during travel to other parts of the world or by contact with someone who is a carrier—either someone who has recently traveled or is a chronic carrier of S.Typhi.

Typhoid Vaccine

Travelers to parts of the world where typhoid fever is common should receive the typhoid vaccine. Risk is greater for travelers to the Indian subcontinent, Latin America, Asia, and Africa who may have exposure to contaminated food and drink.4 Since typhoid vaccine is not 100% effective, it is not a substitute for being careful about what you eat or drink.

During the past 15 years, the two typhoid vaccines licensed in the US have been widely used globally. These vaccines have largely replaced the old heat-phenol inactivated whole-cell vaccine in many countries, including the US.

  • An oral live-attenuated strain of S.Typhi—a weakened strain of S. Typhi that is taken by mouth. Children less than 6 years of age should not receive this vaccine.
  • A parenteral capsular polysaccharide vaccine—a piece of the bacterium that is given by injection. Children less than 2 years of age should not receive this oral vaccine.5

The efficacy of the two licensed vaccines ranges from 50% to 80%. The oral vaccine, for example, has shown a protective efficacy of 62% for at least seven years after the last dose. The inactivated vaccine for its part, showed a 55% efficacy in a recent study in South Africa three years after immunization of children 5 to 16 years of age.2

Both typhoid vaccines have few adverse reactions, and most reactions that do occur are mild—fever, headache or nausea.5

For instance, the Vaccine Adverse Event Reporting System (VAERS) received 1,482 US adverse event reports after typhoid vaccination during the period of 1 July 1990 through 31 June 2002. A total of 321 of these reports involved the polysaccharide vaccine, 345 involved the oral vaccine, 707 involved whole-cell vaccine (which is no longer available in the US), and 109 did not identify the vaccine type.6

Although causal relationships for specific conditions cannot be established from VAERS data, an analysis of these reports identified some unanticipated conditions that may be related to the vaccines: influenza-like syndromes and anaphylaxis (hypersensitivity to the vaccine) after receipt of the oral vaccine and other serious allergic events after receipt of the polysaccharide vaccine. However, VAERS reports do not indicate any unexpected serious side effects that compromise these vaccines’ use for travelers’ prevention of typhoid fever.

References