Q: Which of the following equations correctly calculates the sensitivity of a diagnostic test?

$$\text{Sensitivity} = \frac{\text{True Positives}}{\text{True Positives} + \text{False Negatives}} \times 100\%$$

Question 1

Which of the following best describes the mechanism by which mRNA vaccines, such as those for COVID-19, induce immunity?

Accepted Answer

They inject viral mRNA encapsulated in lipid nanoparticles, which is translated into antigenic proteins that stimulate both humoral and cellular immunity.

Question 2

A patient receives a vaccine containing purified polysaccharide from Streptococcus pneumoniae. Which type of vaccine is this, and what is a key limitation?

Accepted Answer

It is a polysaccharide vaccine; its limitation is poor immunogenicity in children under 2 years old.

Question 3

Which of the following equations correctly calculates the sensitivity of a diagnostic test?

Accepted Answer

$$	ext{Sensitivity} = \frac{	ext{True Positives}}{	ext{True Positives} + 	ext{False Negatives}} 	imes 100\%$$

Question 4

Why are attenuated vaccines generally not recommended for immunocompromised patients?

Accepted Answer

They may revert to a virulent form and cause disease.

Question 5

Which of the following best explains why herd immunity is important in controlling infectious diseases?

Accepted Answer

It reduces the number of susceptible individuals, making outbreaks sporadic and less likely to spread.

Question 6

A laboratory is producing monoclonal antibodies (Mabs) for diagnostic use. What is a key advantage of Mabs over polyclonal antibodies from an infected animal?

Accepted Answer

Mabs are highly specific and uniform, reducing cross-reactivity in tests.

Question 7

Which of the following statements about adjuvants is correct?

Accepted Answer

Adjuvants enhance the innate immune response, often by activating Toll-like receptors.

Question 8

A patient’s serum is tested for antibodies using an indirect ELISA. Which of the following best describes the detection method?

Accepted Answer

Antigen is adsorbed to the well, patient serum is added, and enzyme-linked anti-human antibody binds to any patient antibody present, producing a color change.

Question 9

Which of the following best explains why the oral (Sabin) polio vaccine can sometimes cause polio, but the injected (Salk) vaccine does not?

Accepted Answer

The oral vaccine contains attenuated live virus, which can rarely mutate back to a virulent form, while the injected vaccine contains inactivated virus.

Question 10

Which of the following is a key difference between direct and indirect agglutination tests?

Accepted Answer

Indirect agglutination tests use particles coated with antigen or antibody to detect the presence of antibody or antigen, respectively.

Question 11

A patient’s blood sample is tested for the presence of antibodies to a virus using a viral hemagglutination inhibition test. What result indicates the presence of antibodies?

Accepted Answer

No agglutination of red blood cells occurs because antibodies neutralize the virus.

Question 12

Which of the following best describes the principle of the complement-fixation test?

Accepted Answer

Complement binds to antigen–antibody complexes, and the absence of hemolysis indicates a positive result.

Question 13

Which of the following is a major advantage of producing DNA or mRNA vaccines compared to traditional vaccines?

Accepted Answer

They can be produced rapidly without the need to culture the pathogen.

Question 14

Which of the following best explains why precipitation reactions are only visible in a narrow range of antigen and antibody concentrations?

Accepted Answer

Precipitation occurs at the zone of equivalence, where optimal ratios of antigen and antibody allow for lattice formation.

Question 15

Which of the following is a real-world application of monoclonal antibodies in medicine?

Accepted Answer

They are used to treat diseases such as cancer, COVID-19, and autoimmune disorders.

Question 16

Which of the following best describes the function of an adjuvant in a vaccine?

Accepted Answer

To enhance the immune response to the vaccine antigen.

Question 17

Which of the following is a key reason why vaccination is the only feasible way to control most viral diseases?

Accepted Answer

Viruses cannot be effectively treated once infection occurs, so prevention by vaccination is essential.

Question 18

Which of the following best describes the difference between direct and indirect fluorescent-antibody (FA) tests?

Accepted Answer

Direct FA tests use fluorescent-labeled antibodies to detect antigens in a specimen, while indirect FA tests use a secondary fluorescent-labeled antibody to detect antibodies in serum.

Practical Applications of Immunology: Vaccines and Diagnostic Immunology

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