Researchers conduct a randomized controlled trial to evaluate the efficacy of a novel recombinant vaccine against respiratory syncytial virus (RSV) in older adults. A total of 16,000 healthy volunteers aged 65 years and older are enrolled and randomly assigned in a 1:1 ratio to receive either the vaccine or a placebo. Over a 24-month follow-up period, the investigators record the incidence of severe lower respiratory tract disease (LRTD) confirmed by laboratory testing. The results are summarized in the following table:
| Group | Total Participants | Cases of Severe LRTD |
|---|---|---|
| Placebo | 8,000 | 120 |
| Vaccine | 8,000 | 40 |
Based on these study results, what is the number needed to treat (NNT) to prevent one case of severe LRTD?
Answer: 100 patients
Answer
The number needed to treat (NNT) is 100 patients.
The number needed to treat (NNT) represents the number of patients who need to receive a specific intervention to prevent one additional adverse outcome. It is mathematically defined as the inverse of the absolute risk reduction (ARR). First, we determine the baseline risk in the placebo group: . Next, we determine the risk in the vaccine group: . The ARR is the difference between these two rates: . Finally, the NNT is the inverse of the ARR: . Therefore, 100 older adults must be vaccinated to prevent one case of severe LRTD.
Step-by-Step Solution
Key Concept
Number Needed to Treat (NNT) is calculated as the inverse of the Absolute Risk Reduction (ARR), representing the absolute difference in event rates between the control and experimental groups.