Question:
Which one of the following doses, in lethal flocculating units of Diphtheria Toxoid, is incorporated in DPT vaccine?
Which one of the following doses, in lethal flocculating units of Diphtheria Toxoid, is incorporated in DPT vaccine?
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Recall the standard Lf content fixed for diphtheria toxoid in DPT vaccine.
Updated On: Jul 7, 2026
- 5
- 15
- 25
- 35
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The Correct Option is C
Solution and Explanation
Step 1: Understanding the Concept.
DPT vaccine is a combined vaccine against diphtheria, pertussis, and tetanus. The diphtheria component is a toxoid, meaning the toxin has been treated so it can no longer cause disease but can still trigger the immune system to make protective antibodies. The strength of a toxoid is measured in Lf units, short for Limes flocculation units, which is a way of standardising how much toxoid is present.
Step 2: Key Formula or Approach.
Each vaccine component has a fixed standard content of Lf units per dose, set so the vaccine gives a strong immune response without causing too much local reaction. For diphtheria toxoid in the DPT vaccine, this standard content is 25 Lf per dose. This is a fixed fact used in vaccine manufacturing and quality control, so it needs to be recalled rather than derived.
Step 3: Detailed Explanation.
Option (A), 5 Lf, is too low a value and is not the accepted standard for diphtheria toxoid in DPT.
Option (B), 15 Lf, is also below the standard content used in the combined vaccine.
Option (C), 25 Lf, matches the accepted standard content of diphtheria toxoid incorporated in one dose of DPT vaccine.
Option (D), 35 Lf, is higher than the standard content and is not correct.
Step 4: Final Answer.
The DPT vaccine incorporates diphtheria toxoid at a dose of 25 Lf units.
DPT vaccine is a combined vaccine against diphtheria, pertussis, and tetanus. The diphtheria component is a toxoid, meaning the toxin has been treated so it can no longer cause disease but can still trigger the immune system to make protective antibodies. The strength of a toxoid is measured in Lf units, short for Limes flocculation units, which is a way of standardising how much toxoid is present.
Step 2: Key Formula or Approach.
Each vaccine component has a fixed standard content of Lf units per dose, set so the vaccine gives a strong immune response without causing too much local reaction. For diphtheria toxoid in the DPT vaccine, this standard content is 25 Lf per dose. This is a fixed fact used in vaccine manufacturing and quality control, so it needs to be recalled rather than derived.
Step 3: Detailed Explanation.
Option (A), 5 Lf, is too low a value and is not the accepted standard for diphtheria toxoid in DPT.
Option (B), 15 Lf, is also below the standard content used in the combined vaccine.
Option (C), 25 Lf, matches the accepted standard content of diphtheria toxoid incorporated in one dose of DPT vaccine.
Option (D), 35 Lf, is higher than the standard content and is not correct.
Step 4: Final Answer.
The DPT vaccine incorporates diphtheria toxoid at a dose of 25 Lf units.
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