Oral Typhoid Immunization: A Modern Approach to Disease Prevention

Author : anushka jadhav | Published On : 30 Apr 2024

What is Typhoid Fever?

Typhoid fever is a life-threatening illness caused by the bacterium Salmonella Typhi. The bacteria spreads through contaminated food and water. Symptoms include high fever, weakness, stomach pains, headache, poor appetite, constipation or diarrhea. Without prompt treatment, typhoid fever can be serious and sometimes fatal.

How Does it Work?

The enteric fever vaccine contains live but weakened Salmonella Typhi bacteria. When a person receives the vaccine, the weakened bacteria infect and start replicating in the intestine but do not spread to other parts of the body. This causes the body's immune system to develop protection against the Salmonella Typhi bacteria that causes typhoid fever. If later exposed to the actual disease-causing bacteria through contaminated food or water, the immune system recognizes it and is able to rapidly destroy it before the person gets sick. The enteric fever vaccine provides long-lasting protection of approximately 5 years.

Types Of Enteric Fever Vaccines

There are two types of oral typhoid vaccines available:

- Live Attenuated Vaccine: This was the first enteric fever vaccine developed. It contains live attenuated (weakened) Salmonella Typhi bacteria that do not cause disease but still provoke an immune response. The most commonly used live attenuated enteric fever vaccine is Ty21a.

- Vi Capsular Polysaccharide-Protein Conjugate Vaccine: This newer typhoid vaccine contains killed Salmonella Typhi bacteria coupled to a protein carrier. It provides stronger and longer lasting protection than the live vaccine, especially in young children. The only Vi polysaccharide-protein conjugate vaccine currently licensed is Typbar-TCV.

Efficacy and Recommended Use

Clinical trials have shown that a single dose of enteric fever vaccine is 50-80% effective in preventing typhoid fever. Protection develops approximately 7-10 days after vaccination and lasts for 2-5 years. A booster dose is recommended every 5 years for continued protection, especially for those at high risk such as travelers, military personnel, or health workers stationed in areas where typhoid is common. The enteric fever vaccine is recommended for:

- Travelers going to regions with risk of typhoid fever. It provides protection throughout the entire trip.

- People working in settings associated with the spread of typhoid such as refugee camps or areas with poor sanitation.

- Military personnel deployed to typhoid-endemic areas.

- Children over 6 years of age and adults living in areas where typhoid is common.

Safety and Side Effects

The oral typhoid vaccines are very safe. Common mild side effects reported are mild abdominal pain, diarrhea, fever and headache which usually resolve within 1-2 days. Serious adverse reactions are extremely rare. The live vaccine should not be given to people who have a weakened immune system due to HIV/AIDS, cancer treatment, organ transplantation or elderly due to their decreased ability to fight infection. The conjugate vaccine is suitable for individuals of all ages including children from 6 months.

Precautions After Vaccination

For the live vaccine, it is advised to avoid anti-bacterial medications like antibiotics for 1 week before and after vaccination as it may decrease effectiveness. Good hand washing should be practiced when changing the diapers of vaccinated infants and young children due to the risk of transmission through fecal matter in the stool for 1 week following vaccination. Thorough cooking of food and purification of drinking water is essential when travelling to endemic regions. When used as directed, oral typhoid vaccination provides safe and effective prevention of typhoid fever.

Benefits of Oral Typhoid Vaccines

The main benefits of enteric fever vaccines are:

- Higher immunogenicity: The live bacteria stimulate both mucosal and systemic immunity which provides long-lasting protection compared to injection vaccines.

- Ease of administration: The oral capsules are easy to administer compared to injections, allowing self-or volunteer-administration in mass campaigns. This reduces costs and logistical requirements.

- Thermostability: The live typhoid vaccines do not require refrigeration for storage and transport, making them suitable for use in tropical countries and remote areas lacking cold chain infrastructure.

- Safety: When used as directed, the oral vaccines have an excellent safety profile with mild and self-limiting side effects. This encourages vaccine acceptance.

- Herd immunity: Oral vaccination helps break the chain of typhoid transmission in communities through acquisition of immunity by wider population coverage.

Thus, enteric fever vaccination is a highly effective public health intervention to control typhoid and reduce its socioeconomic burden, especially in endemic developing world contexts. Widespread use can significantly lower the global disease burden of this serious Enteric fever.