body {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
line-height: 1.6;
color: #333;
max-width: 800px;
margin: 0 auto;
padding: 20px;
background-color: #f9f9f9;
}
.calculator-wrapper {
background: #ffffff;
padding: 30px;
border-radius: 12px;
box-shadow: 0 4px 15px rgba(0,0,0,0.1);
margin-bottom: 40px;
border: 1px solid #e0e0e0;
}
.calc-title {
text-align: center;
color: #2c3e50;
margin-bottom: 25px;
font-size: 24px;
border-bottom: 2px solid #3498db;
padding-bottom: 10px;
}
.input-grid {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 20px;
}
@media (max-width: 600px) {
.input-grid {
grid-template-columns: 1fr;
}
}
.group-header {
font-weight: bold;
color: #3498db;
margin-bottom: 10px;
text-transform: uppercase;
font-size: 0.9em;
letter-spacing: 1px;
}
.input-group {
margin-bottom: 15px;
}
.input-group label {
display: block;
margin-bottom: 5px;
font-weight: 500;
color: #555;
}
.input-group input {
width: 100%;
padding: 10px;
border: 1px solid #ddd;
border-radius: 6px;
font-size: 16px;
box-sizing: border-box;
transition: border-color 0.3s;
}
.input-group input:focus {
border-color: #3498db;
outline: none;
}
.calc-btn {
width: 100%;
padding: 15px;
background-color: #27ae60;
color: white;
border: none;
border-radius: 6px;
font-size: 18px;
font-weight: bold;
cursor: pointer;
transition: background-color 0.3s;
margin-top: 10px;
}
.calc-btn:hover {
background-color: #219150;
}
.result-section {
margin-top: 25px;
padding: 20px;
background-color: #f0f7fb;
border-radius: 8px;
display: none;
border-left: 5px solid #3498db;
}
.result-header {
font-size: 14px;
color: #7f8c8d;
text-transform: uppercase;
}
.result-value {
font-size: 36px;
font-weight: bold;
color: #2c3e50;
margin: 10px 0;
}
.result-details {
font-size: 14px;
color: #555;
border-top: 1px solid #dcebf5;
padding-top: 10px;
margin-top: 10px;
}
.detail-row {
display: flex;
justify-content: space-between;
margin-bottom: 5px;
}
.content-article h2 {
color: #2c3e50;
margin-top: 30px;
font-size: 22px;
}
.content-article h3 {
color: #34495e;
font-size: 18px;
margin-top: 20px;
}
.formula-box {
background: #fdf2e9;
padding: 15px;
border-left: 4px solid #e67e22;
margin: 20px 0;
font-family: 'Courier New', monospace;
font-weight: bold;
}
function calculateEfficacy() {
// Get input values
var vacTotal = document.getElementById('vacTotal').value;
var vacCases = document.getElementById('vacCases').value;
var unvacTotal = document.getElementById('unvacTotal').value;
var unvacCases = document.getElementById('unvacCases').value;
var resultDiv = document.getElementById('resultOutput');
// Validation
if (vacTotal === "" || vacCases === "" || unvacTotal === "" || unvacCases === "") {
alert("Please fill in all fields to calculate efficacy.");
return;
}
vacTotal = parseFloat(vacTotal);
vacCases = parseFloat(vacCases);
unvacTotal = parseFloat(unvacTotal);
unvacCases = parseFloat(unvacCases);
if (vacTotal <= 0 || unvacTotal vacTotal || unvacCases > unvacTotal) {
alert("Number of cases cannot exceed total participants.");
return;
}
// 1. Calculate Attack Rates (Risk)
var arv = vacCases / vacTotal; // Attack Rate Vaccinated
var aru = unvacCases / unvacTotal; // Attack Rate Unvaccinated (Control)
if (aru === 0) {
alert("Cannot calculate efficacy: No infections in the control group (Attack Rate Unvaccinated is 0).");
return;
}
// 2. Calculate Vaccine Efficacy
// Formula: VE = (ARU – ARV) / ARU * 100
// Or: VE = (1 – (ARV / ARU)) * 100
var ve = ((aru – arv) / aru) * 100;
var rr = arv / aru; // Relative Risk
// 3. Display Results
document.getElementById('veResult').innerHTML = ve.toFixed(2) + "%";
document.getElementById('aruResult').innerHTML = (aru * 100).toFixed(4) + "%";
document.getElementById('arvResult').innerHTML = (arv * 100).toFixed(4) + "%";
document.getElementById('rrResult').innerHTML = rr.toFixed(4);
resultDiv.style.display = "block";
}
How to Calculate Vaccine Efficacy Rate
Understanding vaccine efficacy is crucial for interpreting clinical trial data and assessing public health tools. Whether you are analyzing data from a Phase 3 trial or studying epidemiology, knowing how to calculate vaccine efficacy (VE) allows you to quantify the percentage reduction in disease incidence in a vaccinated group compared to an unvaccinated group.
What is Vaccine Efficacy?
Vaccine efficacy measures how well a vaccine performs under ideal, controlled conditions, such as clinical trials. It represents the proportionate reduction in disease cases among the vaccinated group. For example, if a vaccine has 95% efficacy, it means that there was a 95% reduction in new cases of the disease in the vaccinated group compared to the unvaccinated (control) group.
It is important to distinguish Efficacy from Effectiveness. Efficacy is determined in controlled trials, while effectiveness measures how well the vaccine works in the real world among diverse populations.
The Vaccine Efficacy Formula
The standard formula for calculating vaccine efficacy relies on comparing the "Attack Rate" (or risk of infection) in the unvaccinated group versus the vaccinated group.
VE = ((ARU – ARV) / ARU) × 100%
Where:
- VE: Vaccine Efficacy (%)
- ARU: Attack Rate in Unvaccinated Group (Infections / Total Unvaccinated)
- ARV: Attack Rate in Vaccinated Group (Infections / Total Vaccinated)
Alternatively, this can be expressed using the Relative Risk (RR):
VE = (1 – Relative Risk) × 100%
Step-by-Step Calculation Example
Let's calculate the efficacy rate using a realistic scenario similar to large-scale mRNA vaccine trials.
Scenario Data:
- Vaccinated Group: 20,000 participants, 10 infections.
- Control Group (Unvaccinated): 20,000 participants, 200 infections.
Step 1: Calculate Attack Rate for Unvaccinated (ARU)
Divide the number of cases by the total number of participants in the control group.
ARU = 200 / 20,000 = 0.01 (or 1%)
Step 2: Calculate Attack Rate for Vaccinated (ARV)
Divide the number of cases by the total number of participants in the vaccinated group.
ARV = 10 / 20,000 = 0.0005 (or 0.05%)
Step 3: Apply the Efficacy Formula
Now, plug these numbers into the primary formula:
VE = (0.01 – 0.0005) / 0.01
VE = 0.0095 / 0.01
VE = 0.95
Step 4: Convert to Percentage
Multiply by 100 to get the percentage.
VE = 95%
This result indicates that the vaccine reduced the risk of infection by 95% compared to no vaccination.
Interpreting the Results
- High Efficacy (>90%): Indicates the vaccine is highly successful at preventing the disease in a controlled setting (e.g., Measles, Polio, COVID-19 mRNA vaccines).
- Moderate Efficacy (50-70%): Common for vaccines against rapidly mutating viruses like Influenza. While lower, these vaccines still significantly reduce severe illness, hospitalization, and death.
- Negative Efficacy: Theoretically possible but rare, indicating the vaccinated group had a higher infection rate than the control group.
Factors Influencing Calculation Accuracy
When calculating efficacy, ensure that the time frame for monitoring both groups is identical. Additionally, the definition of a "case" (e.g., symptomatic vs. asymptomatic) must be consistent across both groups. Variations in exposure levels, demographics, and variants of the pathogen can also impact the final efficacy rate.