INTRODUCTION

Historically, endemic and epidemic cholera commonly has occurred in parts of southern and southeastern Asia. Since 1961, cholera caused by the El Tor biotype has been epidemic throughout much of Asia, the Middle East, and Africa and in certain parts of Europe. Infection is acquired primarily by consuming contaminated water or food; person-to-person transmission is rare. Travelers who follow the usual tourist itinerary and who use standard accommodations in countries affected by cholera are at virtually no risk of infection.

CHOLERA VACCINE

Cholera vaccines *, whether prepared from Classic or El Tor strains, are of limited usefulness. In field trials conducted in areas with endemic cholera, vaccines have been only about 50% effective in reducing the incidence of clinical illness for 3-6 months. They do not prevent transmission of infection. Therefore, the Public Health Service no longer requires cholera vaccination for travelers coming to the United States from cholera-infected areas, and the World Health Organization (WHO) no longer recommends cholera vaccination for travel to or from cholera-infected areas. Surveillance and treatment are sufficient to prevent spread of the disease if it were introduced into the United States.

Vaccine available in the United States is prepared from a combination of phenol-inactivated suspensions of classic Inaba and Ogawa strains of Vibrio cholerae grown on agar or in broth.

VACCINE USAGE

General Recommendations

Vaccine should not be used to manage contacts of persons with imported cases or to control the spread of infection. Repeated vaccination is required or advised sometimes for laboratory workers and airline and ship crews. However, such groups are unlikely to acquire or transmit cholera. Because information on the long-term safety of repeated vaccination is limited, such practices should be discontinued for airline and ship crews except when resolutely demanded by some countries for international travel.

Vaccine is not recommended for infants less than 6 months of age and is not required for travel by most countries.

Vaccination for International Travel

The risk of cholera to U.S. travelers is so low that the vaccine is not likely to benefit most U.S. travelers. Persons using standard tourist accomodations in countries affected by cholera are at virtually no risk of infection. The traveler's best protection against cholera, as well as against many other enteric diseases, is to avoid food and water that might be contaminated.

However, many countries affected or threatened by cholera require evidence of cholera vaccination for entry. One dose of vaccine will usually satisfy entry requirements for persons who anticipate travel to such countries and who will be vaccinated in the United States.

With the threat or occurrence of epidemic cholera, health authorities of some countries may require evidence of a complete primary series of two doses or a booster dose within 6 months before arrival. The complete primary series is otherwise suggested only for special high-risk groups that work and live in highly endemic areas under less than sanitary conditions (Table_1).

Vaccination requirements published by WHO are regularly updated and summarized for travelers by the Public Health Service and distributed to state and local health departments, airlines, travel agents, many physicians, and others. Physicians and travelers should seek information on requirements from these sources.

Physicians administering vaccine to travelers should emphasize that an International Certificate of Vaccination against cholera must be validated for it to be acceptable to quarantine authorities. Validation can be obtained at most city, county, and state health departments as well as many private clinics and physicians' offices. Failure to secure validation may cause travelers to be revaccinated or quarantined. A properly documented certificate is valid for 6 months, beginning 6 days after vaccination or beginning on the date of revaccination if this revaccination is within 6 months of a previous injection.

Data have indicated that persons given yellow fever and cholera vaccines simultaneously or 1-3 weeks apart had initially lower-titered antibody responses to both vaccines. However, seroconversion rates were unaffected, and the clinical importance of these data are unknown. In view of these data, yellow fever and cholera vaccines ideally should be given at least 3 weeks apart. If that is not possible, and both vaccines must be given, then they can be given simultaneously or at any time within the 3-week interval, although a delay in expected yellow fever protection may occur.

Primary Immunization

Complete primary immunization consists of two doses of vaccine given at least 1 week apart. The intradermal route is satisfactory for persons greater than or equal to 5 years of age (Table_1).

Booster Doses

Booster doses may be given every 6 months if necessary for travel or for residence in highly endemic, unsanitary areas. In areas where cholera occurs in a 2-3 month season, protection is best if the booster dose is given at the beginning of the season. The primary series does not need to be repeated for booster doses to be effective.

PRECAUTIONS AND CONTRAINDICATIONS

Reactions

Vaccination often results in 1-2 days of pain, erythema, and induration at the site of injection. The local reaction may be accompanied by fever, malaise, and headache.

Serious reactions following cholera vaccination are extremely rare. If a person has had a serious reaction to the vaccine, revaccination is not advised. Most governments will permit an unvaccinated traveler to proceed if he/she carries a physician's statement of medical contraindication. However, some countries may quarantine such unvaccinated persons or place them under surveillance if they come from areas with cholera.

Pregnancy

No specific information exists on the safety of cholera vaccine during pregnancy. Its use should be individualized to reflect actual need.

• Official name: Cholera Vaccine.

SELECTED BIBLIOGRAPHY

Bart KJ, Gangarosa EJ. Cholera. In: Kelley VC, ed. Brennemann's practice of pediatrics. Vol II, chap. 18c. New York: Harper and Row, 1977:1-12.

Barua D, Burrows W, eds. Cholera. Philadelphia: WB Saunders, 1974. CDC. Health information for international travel, 1988. Atlanta: US Department of Health and Human Services, Public Health Service, 1988; HHS publication no. (CDC)88-8280.

Felsenfeld O, Wolf RH, Dutta NK. Serological responses of Patas monkeys (Erythrocebus patas) to vaccination against cholera and yellow fever. Proc Soc Exp Biol Med 1973;143:548-50.

Gangarosa EJ, Barker WH. Cholera: implications for the United States. JAMA 1974;227:170-1.

Gateff C, Dodin A, Wiart J. Comparaison des reactions serologiques induites par un vaccin anticholerique classique et une fraction vaccinante purifiee associes ou non au vaccin antiamaril. Ann Microbiol (Paris) 1975;126:231-46.

McCormack WM, Chowdhury AM, Jahangir N, et al. Tetracycline prophylaxis in families of cholera patients. Bull WHO 1968;38:787-92.

Philippines Cholera Committee. A controlled field trial on the effectiveness of the intradermal and subcutaneous administration of cholera vaccine in the Philippines. Bull WHO 1973;49:389-94.

Snyder JD, Blake PA. Is cholera a problem for US travelers? JAMA 1982;247:2268-9.

Sommer A, Khan M, Mosley WH. Efficacy of vaccination of family contacts of cholera cases. Lancet 1973;1:1230-2.
Table_1
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TABLE 1. Recommended doses, by volume, for immunization against cholera
=========================================================================
                               Route and age
             --------------------------------------------------
             Intradermal *      Subcutaneous or intramuscular
             -------------     --------------------------------
Dose no.        >=5 yrs        6 mos-4 yrs   5-10 yrs   >10 yrs
---------------------------------------------------------------
1 and 2         0.2 mL           0.2 mL       0.3 mL    0.5 mL

Boosters        0.2 mL           0.2 mL       0.3 mL    0.5 mL
---------------------------------------------------------------
* Higher levels of protection (antibody) may be achieved in children <5
  years old by the subcutaneous or intramuscular routes.
=========================================================================

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