Epidemiology & Prevention USMLE Step 1 Practice Question
A 45-year-old woman participates in a randomized influenza vaccine trial. She receives the inactivated influenza vaccine and remains asymptomatic throughout the season with normal vital signs (BP 118/76, HR 72, RR 14, Temp 37°C). Over one influenza season, 6 of 1,000 vaccinated participants develop symptomatic infection confirmed by RT-PCR, compared to 30 of 1,000 unvaccinated controls. No serious adverse events occur in the vaccine group. Which of the following represents the vaccine efficacy of this immunization?
Answer choices
- A40%
- B80%Correct answer
- C20%
- D60%
- E94%
- F88%
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