Oral Cholera Vaccine

Cholera is a severe diarrheal disease caused by the bacterium Vibrio cholerae, primarily affecting regions with inadequate sanitation and limited access to clean drinking water. The disease is known for its rapid spread, leading to large outbreaks that can cause significant morbidity and mortality. To combat cholera, oral cholera vaccines (OCVs) have been developed as an essential preventive measure.

This article provides a detailed overview of the oral cholera vaccine, its effectiveness, global availability, challenges, and policy considerations, especially in endemic regions like India.

Understanding Cholera and Its Impact

Cholera is caused by Vibrio cholerae serogroups O1 and O139, which produce a toxin leading to severe watery diarrhea. Without proper treatment, the disease can lead to dehydration, shock, and death. Children under five years of age are particularly vulnerable in endemic areas.

Historically, major cholera outbreaks have been linked to poor hygiene and sanitation, as seen in the Latin American epidemic. The key to controlling cholera lies in improving water supply, sanitation, and hygiene (WASH), along with timely disease diagnosis and management.

Available Oral Cholera Vaccines (OCVs)

Several oral cholera vaccines are available in the global market, including:

1. Dukoral (Sweden)
2. Shanchol (India)
3. Euvichol (South Korea)
4. OraVacs (China)

These vaccines provide significant protection against cholera and are commonly used in mass vaccination campaigns.

Efficacy and Duration of Protection

Clinical trials have demonstrated that OCVs have a two-dose efficacy of 58% and can remain effective for up to three years with a protection rate of 76%. In some cases, efficacy has been recorded for as long as five years.

Although the standard practice involves administering two doses 14 days apart, a single-dose regimen has also shown short-term protection, with a pooled efficacy of 69% within the first year. This has important implications for outbreak response and emergency vaccination campaigns.

Cholera Vaccine Deployment and Global Stockpile

OCVs are distributed globally for both emergency and preventive use. The Global OCV Stockpile, managed by the International Coordinating Group (ICG), ensures that vaccines are available for rapid deployment in cholera outbreaks. Organizations involved in vaccine stockpile management include:

1. World Health Organization (WHO)
2. United Nations Children's Fund (UNICEF)
3. Médecins Sans Frontières (MSF)
4. International Federation of Red Cross and Red Crescent Societies (IFRC)

Only WHO-prequalified vaccines are included in the stockpile. Due to global supply limitations, vaccine allocations are reviewed before being released to affected countries.

Cholera Vaccine in India: Challenges and Policy Considerations

India, one of the cholera-endemic regions, has yet to establish a robust policy for OCV deployment. The major challenges include:

• Lack of policy directives: Unlike other vaccines, OCV delivery does not have a structured national program.
• Cost-effectiveness concerns: There is limited data on whether mass vaccination is more effective than routine immunization.
• Integration into the Expanded Programme on Immunization (EPI): It is still uncertain if OCVs can be incorporated into India’s routine immunization schedule, particularly at the age of measles vaccination.

Research suggests that mass vaccination campaigns in high-risk areas (1-14 years age group) could be beneficial, followed by routine immunization. However, further studies on vaccine safety, efficacy in infancy, and hotspot surveillance are required before full-scale implementation.

OraVacs: A New Development in Oral Cholera Vaccination

A relatively new cholera vaccine, OraVacs, is an enteric-coated capsule containing recombinant cholera B subunit and inactivated whole-cell (V. cholerae O1 classical and El Tor biotypes). OraVacs is similar to Dukoral in composition and offers protection against cholera and traveler's diarrhea caused by enterotoxigenic Escherichia coli (ETEC).

OraVacs Administration and Availability

1. Dosage schedule: Three capsules taken on Days 0, 7, and 28.
2. Target group: Children (2 years and older), teenagers, and adults.
3. Licensing status: Currently licensed in China and the Philippines.
4. Safety and immunogenicity: Clinical trials indicate that OraVacs is safe and induces an immune response; however, efficacy data is still lacking.

Future Directions and Conclusion

The role of oral cholera vaccines in preventing and controlling cholera outbreaks is undeniable. While OCVs provide effective short- and long-term protection, their deployment must be integrated with broader public health measures, including WASH interventions and public awareness campaigns.

For countries like India, establishing a clear policy framework for OCV use, integrating it into national immunization programs, and conducting further research on vaccine efficacy in infants and high-risk populations is essential.

With continued advancements in vaccine research and increased production capacities, OCVs can play a crucial role in reducing the global burden of cholera, ultimately saving lives and improving public health outcomes.