2. Explain how the bacterium is attenuated in the Vivotif vaccine and why this a

Question

2. Explain how the bacterium is attenuated in the Vivotif vaccine and why this attenuation prevents the the bacteria in the vaccine from causing typhoid fever. (Note: You will find the answer in the product insert for the drug under “Clinical Pharmacology.” Be specific and thorough in your response.)

4. The Typhim Vi® vaccine is a(n) _____ vaccine.

a. sub-unit

b. inactivated

c. attenuated

5. Explain why re-immunization with the Vivotif® vaccine is recommended every five years, but is recommended every two years for the Typhim Vi® vaccine. (Note: Use your knowledge of immunology to answer this question).

Helpful Links:

Typhoid Vaccine Information

• Immunization Action Coalition Click on “Typhoid.” http://www.immunize.org/fda/

• World Health Organization [WHO] Click on “Typhoid” http://www.who.int/immunization/diseases/en/

Explanation / Answer

Ans 1) Attenuation is the process of using live heat killed microbes as injection to generate the immunity. The Vivotif is a live attenuated vaccine which is only meant for oral vaccination and it contains attenuated strain of Salmonella typhi Ty21a. The strain is grown under controlled condition in fermentors which majorly consists of yeast extract, acid digest of casein, dextrose and galactose. After the cultivation is over, the bacteria is collected by centrifugation and is mixed with stabilizer that contains sucrose, ascorbic acid and amino acids. This is followed by lyophilization. The lyophilized bacteria is mixed with lactose ad magnesium stearate and then filled in the gelatin capsules. The gelatin capsule are enteric coated so that are not digested by acids in the stomach.

Ans 2) c) Attenuated

It is a attenuated vaccine as it consists of heat killed strain of the pathogen which helps in imparting the immunity against the microbial attack.

Ans 5) The re-immunization with the Vivotiff vaccine is 5 years and Typhim Vi vaccine is two years where there is continuous exposure to Salmoneall serotype Typhi. The time frame is different as in the former the occurrence of the infection is less due to its lower prevalence and the memory cells are able to start forming an immunity to fight back the infection by the micro-organisms. However, in the later re-immunization is important as booster shot so that it keeps the level of the memory cells high and maintain a stable population of the same to fight against the infection. The booster dose is a reminder to our immune system to system so that it maintains the required antibodies.

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