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Canada Communicable Disease Report
An Advisory Committee Statement (ACS) STATEMENT ON ORAL CHOLERA VACCINATIONIntroduction Infection with Vibrio cholerae, a toxin-producing bacteria, presents clinically as profuse watery diarrhea. If untreated, severe fluid loss can lead to rapid dehydration, cardiovascular system collapse, and kidney failure. The spectrum of illness is wide, with both mild and asymptomatic cases occurring more frequently than severe disease. Two serogroups, O1 and O139 (Bengal) have been implicated in human epidemics. Within the serogroup O1 are the classical and El Tor biotypes. Cholera infection is associated with poor sanitation, often due to inadequate sewage and water treatment facilities in non-industrial countries. Infection is generally acquired from contaminated water or food, particularly undercooked or raw shellfish and fish. In 1997, no cases of cholera were reported in Canada. In 1996, four cases were reported. These were all related to foreign travel and did not result in any secondary spread. For the traveller, emphasis must be placed on personal hygiene, and food and water precautions; these measures appear to be the most effective protection against cholera. Cholera Vaccine The World Health Organization indicates that, since 1992, no country or territory has required a certificate of vaccination against cholera from international travellers. Parenteral, inactivated cholera vaccine offers short, limited effectiveness and is not recommended for Canadians travelling to endemic areas. Oral Cholera Vaccine Oral live attenuated cholera vaccine, CVD 103-HgR (Mutachol®) has recently been licenced in Canada. Cloned strains of V. cholerae are used to prepare the live attenuated vaccine. The oral cholera vaccine is administered as a single dose with the provided buffer solution, mixed as a drink in cold or lukewarm water. It should be given 1 hour before food or drink. It is approved for adults and children > 2 years of age. The vaccine also contains aspartame (a phenylalanine derivative) which is added as a sweetener. The buffer solution contains sodium bicarbonate, ascorbic acid, and lactose which serve to neutralize gastric acid. Safety Randomized controlled studies have been carried out in several thousand subjects in a number of cholera-endemic and non-endemic areas, and have demonstrated good safety of the vaccine(1-5). Immunogenicity Several studies have shown a good immune response with seroconversion rates > 90% following a single oral dose of the vaccine(1-7). Seroconversion occurred as early as 8 days after administration of the vaccine and lasted for 6 months. Protective efficacy of the vaccine was tested in volunteers challenged with pathogenic V. cholerae of both biotypes and serotypes. Complete protection against the classical biotype was demonstrated in 82% to 100% of subjects, and in 62% to 67% of subjects exposed to the El Tor biotype. However, even when the vaccine did not provide complete protection, no volunteer lost > 1 L diarrheal fluid/24 hours. No cholera vaccine currently available has been shown to be protective against the O139 Bengal strain that emerged in south Asia starting in 1992. Adverse reactions The side-effect profile for the vaccine group was similar to the control (placebo) group. Adverse reactions were mild in nature and of short duration. They included nausea, abdominal cramps, and diarrhea(1-5). Booster dose An optimal booster dose or interval has not yet been established(7). However, the manufacturer recommends that a repeat dose be given every 6 months if indicated. Contraindications and precautions Hypersensitivity to the vaccine or the buffer components is a contraindication to further doses. Patients with phenylketonuria must be aware that the vaccine contains aspartame (a phenylalanine derivative). The vaccine should not be given during an acute febrile illness or to any person with acute gastrointestinal disease. Since it is a live vaccine, it should be used with caution in immunocompromised or immunosupppressed individuals, pregnant women, or nursing mothers. A risk/benefit analysis should be used to determine if an individual in these groups should be immunized. It is not known whether the vaccine is excreted in human milk. The safety and efficacy of the vaccine has not been established in children < 2 years of age and therefore it is not recommended for use in this age group. Antibiotics may interfere with the effectiveness of the vaccine. It is recommended that individuals on antibiotic therapy wait 7 days after the completion of therapy before taking the oral cholera vaccine. Antimalarial prophylaxis, specifically chloroquine and doxycycline, may interfere with the effectiveness of the vaccine and therefore antimalarial prophylaxis with these medications should start no sooner than 7 days after administration of the oral cholera vaccine. Antimalarial prophylaxis with mefloquine or proguanil does not interfere with the effectiveness of the oral cholera vaccine and therefore can be administered simultaneously. The administration of oral typhoid vaccine (Ty21a) capsules and oral cholera vaccine should be separated by at least 8 hours. The newer oral typhoid vaccine (Ty21a) sachets do not need to be separated from the oral cholera vaccine; the two can be given together, mixed with a single sachet of buffer. The concomitant administration of oral polio vaccine or yellow fever vaccine does not interfere with the immune response to oral cholera vaccine. Oral Cholera Vaccination in the Prevention of Travellers' Diarrhea The oral cholera vaccine (CVD 103-HgR) has not been shown to offer protection against enterotoxigenic Escherichia coli (ETEC)-associated diarrhea which is a common cause of diarrhea in travellers. However, an experimental vaccine containing B-subunit/whole-cell oral cholera vaccine, which is not currently licenced in Canada, may offer some protection against ETEC-associated diarrhea(8). Cholera Disease Risk Assessment Most travellers visiting an area where cholera occurs are at very low risk of acquiring infection. The estimated risk of cholera disease in European or North American travellers to endemic areas is one to two cases per million trips(9). Travellers who may be at increased risk for acquiring cholera (e.g. health professionals working in endemic areas or aid workers in refugee camps) may benefit from vaccination. A detailed, individual risk assessment should be made in order to determine which travellers may benefit from vaccination. Recommendations Table 1 below presents evidence-based medicine categories for the strength and quality of the evidence for each of the recommendations that follow.
Table 1 Strength and quality of evidence summary sheet(10)
References
* Members: Dr. K. Kain (Chairman); H. Birk; M. Bodie-Collins (Executive Secretary); Dr. S.E. Boraston; Dr. H.O. Davies; Dr. K. Gamble; Dr. L. Green; Dr. J.S. Keystone; Dr. K.S. MacDonald; Dr. J.R. Salzman; Dr. D. Tessier. Ex-Officio Members: Dr. E. Callary (HC); R. Dewart (CDC); Dr. E. Gadd (HC); Dr. C.W.L. Jeanes; Dr. H. Lobel (CDC); Dr. A. McCarthy (DND). Liaison Representatives: Dr. R. Birnbaum (CSIH); S. Kalma (CUSO); Dr. V. Marchessault (CPS); Dr. H. Onyette (CIDS); Dr. R. Saginur (CPHA); Dr. F. Stratton (ACE); Dr. B. Ward (NACI).
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Last Updated: 2002-11-08 |