Cholera Vaccination

Cholera is an acute water-borne diarrhoeal infection caused by the enterotoxin subunit-A of Vibrio cholerae.¹ Cholera is prevalent in areas with poor sanitation and food and water hygiene and constitutes a major global public health problem.¹ Without treatment, severe infection has a mortality rate of 30-50%.² Oral cholera vaccines are safe, immunogenic and effective but must not be considered a substitute for basic preventative measures such as clean water and sanitation.³

• Epidemiology - the disease is endemic to parts of Africa, Asia, the Middle East and South America.³ Large outbreaks are common after natural disasters or in populations displaced by war, where there is inadequate sewage disposal and contaminated water.¹ Over 100 000 cases of cholera and 2345 associated deaths were reported to the WHO in 2004, although it is estimated that figures represent only 5-10% of actual worldwide cases.³
• Epidemics and pandemics - two serotypes of Vibrio cholerae cause epidemic cholera (serotype 01 and serotype 0139). Serotype 01 is further divided into classical and El Tor biotypes. Outbreaks caused by the classical biotype are infrequent whereas V. cholerae El Tor now predominates and is responsible for the current seventh cholera pandemic.⁴ Serotype 0139 emerged in 1992 and quickly spread through Asia. It is now responsible for almost 60% of recent cholera cases in China and the threat of pandemic remains.³
• United Kingdom - an average of only 10 cases of cholera are imported into the UK annually. The most common serotype is V. cholerae El Tor and most infections are acquired on the Indian sub-continent.⁵ The risk of cholera for most travellers to endemic areas is very low. The overall incidence of cholera in travellers is only 2-3 per million but for those staying in areas of outbreaks the incidence rises to 5 per thousand.¹

The oral cholera vaccine has limited recommended uses.Cholera vaccine is not licensed for use as an infection control tool in the management of cholera contacts or for prevention of travellers' diarrhoea. The vaccination must not be used as an alternative to standard hygiene precautions, which remain the most effective preventative measures for all food and water-borne diseases.⁶

• Travellers - the oral cholera vaccine is licensed for travellers to endemic/ epidemic areas, aged over 2 years who are at particular risk of serious disease from V. cholerae(serotype 01). Immunisation is recommended for:
  • Relief or disaster aid workers
  • Travellers intending to stay for prolonged periods in areas with limited medical facilities
  Certification of vaccination against cholera is no longer a requirement for entry into any country.⁶
• Laboratory workers - immunisation is recommended for individuals who may be regularly exposed to V. cholerae serotype 01 at work.

The vaccine confers specific protection against V. cholerae serotype 01. It is therefore ineffective for prevention of infection with non-01 strains including V. cholerae serotype 0139.
Oral cholera vaccines are safe and offer good protection.⁷ Trials of the primary immunisation course using an early vaccine formulation showed an efficacy rate of 85% against El Tor disease at 6 months and 50% after 3 years. Due to cross-immunity to heat-labile enterotoxin, the vaccine also provides moderate, short-term protection against many strains of enterotoxic Escherichia coli.⁸

The preparation Dukoral® is the only cholera vaccine licensed in the UK. It consists of four inactivated strains of V. cholerae serotype 01 combined with non-toxic, recombinant cholera toxin subunit-B.⁹ Oral administration stimulates an efficient, local secretory IgA antitoxin response at the intestinal epithelium. The traditional parenteral whole-cell cholera vaccine provided only maximum 50% protection for 3-6 months and was associated with significant adverse reactions. The use of parenteral vaccines is no longer recommended.¹⁰

Food, drink and oral medications must be avoided for one hour before and after vaccination. Effervescent sodium hydrogen carbonate granules are dissolved in water as per manufacturer's instructions and mixed with 3mls of vaccine suspension. The solution must be ingested within 2 hours of reconstitution.

The oral cholera vaccine can be given at the same time as other injected vaccines.

• Primary immunisation

1. Adults and children over 6 years of age - two doses of oral vaccine are given with a 1-6 week interval.
2. Children aged 2-6 years - three doses of vaccine are necessary but each dose is given with a similar 1-6 week interval.
3. Should more than 6 weeks elapse between any doses, the primary immunisation course must be restarted. All individuals must complete the immunisation course at least 1 week prior to potential exposure.⁸

• Boosters - the optimal booster dose or interval has not been established but if indicated, the manufacturer recommends a single booster to augment immunity.⁸

1. Adults and children over 6 years of age A booster can be given 2 years after the primary course. If more than 2 years has elapsed since cholera vaccination the primary course must be repeated.
2. Children aged 2-6 years - a booster dose is given after 6 months.

The oral cholera vaccine should not be administered to patients with:

• Confirmed anaphylactic reaction to oral cholera vaccine
• Confirmed anaphylactic reaction to formaldehyde or any of the components of the vaccine
• Acute illness with systemic upset
• Acute gastro-intestinal illness

• Pregnancy and breast-feeding - it is unlikely that vaccination of pregnant or breast-feeding women with inactivated bacteria or toxoids is associated with adverse outcomes. However no data is available regarding the safety of oral cholera vaccine in such situations. The vaccine should be considered if the risk of cholera exposure is high.
• Immunosuppression including HIV - immunosuppressed individuals must be considered for cholera vaccination according to the recommendations above but such patients may not raise adequate immunological responses.

The oral cholera vaccine is generally well tolerated but reported side-effects include:

• Gastro-intestinal symptoms of diarrhoea, nausea, vomiting, abdominal pain or cramps
• Arthralgia, rash, paraesthesia and flu-like syndrome occur occasionally