Vi capsular polysaccharide vaccine

Vi capsular polysaccharide vaccine, also known as Vi vaccine, is a type of vaccine that provides protection against typhoid fever caused by the bacterium Salmonella enterica serovar Typhi. This vaccine is composed of the Vi polysaccharide, which is a major component of the outer capsule of the bacterium. In this article, we will explore the Vi capsular polysaccharide vaccine in detail, including its composition, mechanism of action, efficacy, and side effects.

Composition

The Vi capsular polysaccharide vaccine is made from purified Vi polysaccharide extracted from the outer capsule of Salmonella enterica serovar Typhi. The Vi polysaccharide is chemically linked to a carrier protein, such as tetanus toxoid or diphtheria toxoid, to enhance its immunogenicity. This conjugation process allows the immune system to recognize and mount a response against the Vi polysaccharide, leading to the production of specific antibodies.

Mechanism of Action

Upon administration, the Vi capsular polysaccharide vaccine stimulates the immune system to produce antibodies against the Vi polysaccharide. These antibodies bind to the Vi polysaccharide on the surface of Salmonella enterica serovar Typhi, preventing the bacterium from invading and causing infection. Additionally, the vaccine induces a memory response, which means that the immune system can quickly recognize and respond to future encounters with the bacterium.

Efficacy

The Vi capsular polysaccharide vaccine has been shown to be highly effective in preventing typhoid fever caused by Salmonella enterica serovar Typhi. Clinical trials have demonstrated that the vaccine provides protection in approximately 70-80% of vaccinated individuals. However, it is important to note that the vaccine does not provide complete protection, and breakthrough infections can still occur in some cases. Therefore, it is recommended to combine vaccination with other preventive measures, such as safe food and water practices, to further reduce the risk of infection.

Side Effects

The Vi capsular polysaccharide vaccine is generally safe and well-tolerated. Common side effects include pain, redness, or swelling at the injection site. Some individuals may also experience mild systemic symptoms, such as fever, headache, or fatigue, which usually resolve within a few days. Serious adverse events are rare but can occur. It is important to consult a healthcare professional if any concerning symptoms or reactions develop after vaccination.

Internal Links

To learn more about typhoid fever, click here. To understand the importance of vaccination, click here. To explore other vaccines, click here.

References

1. World Health Organization. Typhoid vaccines: WHO position paper – March 2018. Weekly Epidemiological Record. 2018; 93(12):153-172. 2. Date KA, Bentsi-Enchill AD, Fox KK, et al. Typhoid Fever Surveillance and Vaccine Use—South-East Asia and Western Pacific Regions, 2009–2013. MMWR Morb Mortal Wkly Rep. 2014; 63(35): 855-860.

3. World Health Organization. Typhoid vaccines: WHO position paper – March 2018. Available at: [1]. Accessed on 10th October 2021.

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