Vaccine Efficacy Calculator
Calculate the effectiveness of a vaccine based on clinical trial data using standard epidemiological formulas.
How to Use This Calculator
- Enter the number of cases in the vaccinated group
- Enter the number of cases in the unvaccinated (placebo) group
- Enter the total number of participants in each group
- Select the study type and confidence level
- Click Calculate to see the vaccine efficacy results
Formula Used
Vaccine Efficacy (VE) = (1 - Relative Risk) × 100%
Relative Risk (RR) = (Cases in vaccinated / Total vaccinated) / (Cases in unvaccinated / Total unvaccinated)
Where:
- VE = Vaccine efficacy expressed as a percentage
- RR = Relative risk of infection in vaccinated vs. unvaccinated groups
- Higher VE values indicate more effective vaccines
Example Calculation
Real-World Scenario:
In a clinical trial for a new COVID-19 vaccine, researchers compared infection rates between vaccinated and unvaccinated groups.
Given:
- Cases in vaccinated group = 8
- Cases in unvaccinated group = 162
- Total in vaccinated group = 20,000
- Total in unvaccinated group = 20,000
Calculation:
Attack rate in vaccinated = 8/20,000 = 0.0004 (0.04%)
Attack rate in unvaccinated = 162/20,000 = 0.0081 (0.81%)
Relative Risk = 0.0004/0.0081 = 0.049
Vaccine Efficacy = (1 - 0.049) × 100% = 95.1%
Result: The vaccine has an efficacy of 95.1%, meaning it reduces the risk of infection by 95.1% compared to not receiving the vaccine.
Why This Calculation Matters
Practical Applications
- Evaluating new vaccine candidates in clinical trials
- Comparing effectiveness between different vaccine brands
- Monitoring vaccine performance against new variants
Key Benefits
- Standardized metric for comparing vaccine performance
- Informs public health policy and vaccination strategies
- Helps healthcare professionals make evidence-based recommendations
Common Mistakes & Tips
Frequently Asked Questions
References & Disclaimer
Medical Disclaimer
This calculator is for educational purposes only and should not be used for medical decision-making. Vaccine efficacy calculations should be performed by qualified researchers and healthcare professionals. Always consult with healthcare providers for medical advice.
References
- WHO Vaccine Efficacy Guidelines - Methodological considerations for COVID-19 vaccine efficacy trials
- CDC Vaccine Efficacy Resources - Guidance on interpreting vaccine efficacy and effectiveness
- New England Journal of Medicine: COVID-19 Vaccine Efficacy - Clinical trial methodology and interpretation
Accuracy Notice
This calculator provides estimates based on the data entered. Actual vaccine efficacy may vary due to factors not accounted for in this simplified calculation, such as population characteristics, variant differences, and time since vaccination.
About the Author
Kumaravel Madhavan
Web developer and data researcher creating accurate, easy-to-use calculators across health, finance, education, and construction and more. Works with subject-matter experts to ensure formulas meet trusted standards like WHO, NIH, and ISO.