Covid Event Risk Calculator
Estimate how many infected people may attend an event based on local prevalence, hidden cases, and gathering size.
What Is the COVID Event Risk Calculator?
Planning a gathering, classroom, or workplace event during respiratory virus seasons means estimating how likely it is that at least one attendee is currently infected. This tool models expected infected attendees from local prevalence and group size. For individual health risk, see the COVID Mortality Risk Calculator.
How the Estimate Works
You can enter detected active cases from a recent 14-day window plus local population, or enter infection prevalence directly. A hidden-case multiplier (default 4) accounts for undetected infections when using reported case counts. Expected infected attendees equals event size multiplied by prevalence. The probability that at least one infected person attends uses the complement rule: $1 - (1 - p)^n$.
Reducing Event Risk
Ventilation, masking during high transmission periods, staying home when ill, and limiting crowding all reduce exposure. Outdoors and smaller groups lower the chance that someone infectious is present.
Frequently Asked Questions
What is the hidden case multiplier?
Early pandemic research suggested many infections were never tested. A multiplier of 4 means total infections are estimated as detected cases times five (detected plus four hidden per detected case).
Why use a 14-day case window?
A typical COVID infection lasts about two weeks. Summing cases over that window approximates currently active infections in an area.
Does a low expected count mean zero risk?
No. Expected values are averages. Even small probabilities matter in large or repeated gatherings, especially for vulnerable attendees.
Can I enter prevalence directly?
Yes. Switch to prevalence mode if you already know the fraction of the population currently infected from wastewater, surveys, or surveillance models.
Is this updated with live data?
You supply local inputs. Automated state feeds change over time, so manual entry keeps the calculator useful for any date or region.
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