Background

• Cholera is an acute diarrhoeal infection caused by the enterotoxin subunit-A of Vibrio cholerae.
• Cholera is a water-borne infection caught through ingestion of faecally contaminated water or shellfish.
• Person-to-person spread via the faeco-oral route can also occur.
• The incubation period is usually 2-5 days. However, it can sometimes be a few hours.
• 75% of those infected are asymptomatic.^[1]
• Cholera is prevalent in areas with poor sanitation and food and water hygiene and constitutes a major global public health problem.
• Without treatment, severe infection has a mortality rate of 30-50%.
• The disease is endemic to parts of Africa, Asia, the Middle East and South America.
• Large outbreaks are common after natural disasters or in populations displaced by war, where inadequate sewage disposal and contaminated water exist.
• 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 subcontinent.
• The risk of cholera for most travellers to endemic areas is very low.

Indications for vaccine - UK recommendations

• Cholera vaccine is not licensed for use as an infection control tool in the management of cholera contacts or for prevention of travellers' diarrhoea.^[2]
• 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.
• Immunisation can be considered for the following:
  • Aid workers helping in disaster relief or refugee camps.
  • Backpackers travelling to remote areas where access to medical care is likely to be limited.

Certification of vaccination against cholera is no longer a requirement for entry into any country.

Efficacy

The vaccine confers specific protection against V. cholerae serotype O1. It is therefore ineffective for prevention of infection with non-O1 strains including V. cholerae serotype O139. Oral cholera vaccines are safe and offer good protection.

The currently available oral killed whole cell vaccines can prevent 50-60% of cholera episodes during the first two years after the primary vaccination schedule.^[3]

Preparations

The preparation Dukoral® is the only cholera vaccine licensed in the UK. It consists of four inactivated strains of V. cholerae serotype O1 combined with nontoxic, recombinant cholera toxin subunit-B.^[2] 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.

Administration

Food, drink and oral medications must be avoided for one hour before and one hour after vaccination. Effervescent sodium hydrogen carbonate granules are dissolved in water (150 ml for adults, and pour half away for children aged 2-6 years) and mixed with 3 mls of vaccine suspension.^[2] The solution must be ingested within two hours of reconstitution.

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

Schedule^[2]

Primary immunisation:

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

Boosters - a single booster to augment immunity is recommended:

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

Immunisation should be completed at least one week prior to travel.

Contra-indications

The oral cholera vaccine should not be administered to patients with:^[4]

• Confirmed anaphylactic reaction to oral cholera vaccine.
• Confirmed anaphylactic reaction to any of the components of the vaccine.

The vaccine should be delayed in those who are suffering form an acute gastrointestinal illness. Pre-existing gastrointestinal illnesses are not contra-indications to the vaccine.

Precautions

• 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 are 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.

Adverse reactions

The oral cholera vaccine is generally well tolerated but reported side-effects include:^[4]

• Gastrointestinal symptoms of diarrhoea, nausea, vomiting, abdominal pain or cramps occurring in up to 1 in 100 cases.
• Arthralgia, rash, paraesthesia and flu-like syndrome which can occur rarely.