Vaccine Efficacy Calculator

VE from vaccinated and unvaccinated incidence rates.

Medical Disclaimer

This calculator is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about your health. Never disregard professional medical advice or delay seeking it because of results from this tool.

Inputs

Cases in vaccinated group

Total vaccinated

Cases in unvaccinated group

Total unvaccinated

Tab to move between fields

Results

Vaccine efficacy (%)

75%

Relative risk0.25

Absolute risk reduction (%)0.6%

Number needed to vaccinate167

95% CI lower (%)59.22%

95% CI upper (%)84.67%

How to Use This Calculator

Enter Cases in vaccinated group, Total vaccinated, and Cases in unvaccinated group.
Set Total unvaccinated.
Review the Vaccine efficacy (%) (%) result.
Use Relative risk and Absolute risk reduction (%) (%) to inform your decision.

How the result changes with Total vaccinated

Total vaccinated	Vaccine efficacy (%)
1,000,001	99.75%
3,500,001	99.93%
6,500,000	99.96%
9,000,000	99.97%

What each input means

Cases in vaccinated group: Number of disease cases among vaccinated individuals.
Total vaccinated: Total number of vaccinated individuals in the study.
Cases in unvaccinated group: Number of disease cases among unvaccinated individuals.
Total unvaccinated: Total number of unvaccinated individuals in the study.

What each result means

Vaccine efficacy (%): Percentage reduction in disease risk among vaccinated vs unvaccinated.
Relative risk: Risk ratio of vaccinated vs unvaccinated (lower = better protection).
Absolute risk reduction (%): Absolute difference in attack rates.
Number needed to vaccinate: People to vaccinate to prevent one case.
95% CI lower (%): Lower bound of 95% confidence interval for VE.
95% CI upper (%): Upper bound of 95% confidence interval for VE.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Cases in vaccinated group = 20, Total vaccinated = 10000, Cases in unvaccinated group = 80, Total unvaccinated = 10000 = 4 input(s) provided
Calculate Vaccine efficacy
Vaccine efficacy = attackRateUnvacc > 0
75 = 75%
Calculate Relative risk
Relative risk
0.25 = 0.25
Calculate Absolute risk reduction
Absolute risk reduction
0.6 = 0.6%