There is no point reaching for a calculator that cannot show its working. This one starts from population and what’s your vaccine? and reports people saved by vaccines, after vaccination 💉 and before vaccination, so you can see how each answer follows from the numbers you entered.
What Is the Vaccine Efficacy Calculator?
The vaccine efficacy calculator gives you an estimate of people saved by vaccines, after vaccination 💉 and before vaccination based on population and what's your vaccine?.
It is a quick reference figure rather than a diagnosis, and it is most useful for tracking how a number moves over time rather than for interpreting a single reading.
How the Vaccine Efficacy Estimate Is Worked Out
The calculation follows published reference relationships, so it is a reasonable approximation when the inputs are accurate. It assumes an average adult and does not account for individual variation.
If you are comparing two people, or the same person over a period of weeks, keep the method and the inputs identical. A change in the method can easily look like a change in the person.
What This Calculator Does Not Do
It does not diagnose anything, and it does not replace advice from a clinician. If a figure comes out at an extreme, or if it differs sharply from what you expect, that is a reason to speak to a professional rather than to adjust the inputs.
Nothing you type here is stored or sent anywhere. The whole calculation happens in your browser.
A Worked Example
Working through an example, with population set to 10, what's your vaccine? set to 0.08, the calculator returns before vaccination of 1.9, and after vaccination 💉 of 0.15, and people saved by vaccines of 1.75. Substitute your own figures and the same steps produce the same kind of answer.
Frequently Asked Questions
What do I need to work out people saved by vaccines?
Enter population and what's your vaccine?. The calculator then works through the relationship and reports people saved by vaccines, after vaccination 💉 and before vaccination.
What does the vaccine efficacy actually calculate?
It takes population and what's your vaccine? and converts them into people saved by vaccines, after vaccination 💉 and before vaccination using the standard relationship for this problem. Each step is applied in turn, so every output is traceable back to the numbers you typed in.
How should I enter population?
Use the value you actually have, in the unit shown next to the field. Enter every value in the same unit system. The calculator assumes the figures you supply are consistent, so it cannot correct a mistake that happens before the calculation starts.
Is the answer exact?
It is as exact as the formula and the inputs allow. The method itself is the standard one for this problem, so the only sources of error are the figures you enter and the precision you ask for.
Can I use this for a quick estimate as well as a precise answer?
Yes. The calculator is built for quick checks, so round your inputs to a sensible number of significant figures and the result will be just as useful. If you need more precision, keep the same method and add digits to the inputs rather than adjusting the method itself.