Vaccine immunity calculator

The free browser tool and the API share the same pure JavaScript library, so interactive checks and automated tasks always agree.

How remaining vaccine-induced protection is estimated

This calculator uses a fixed half-life of twelve months: remaining protection halves every year after the last dose, which is equivalent to multiplying the peak by the exponential of minus the natural logarithm of two times months divided by twelve.

Input contract, outputs, and error behaviour

Failed validation is not billed. There is no pathogen table, no age adjustment, no immunocompromise flag, and no calendar date in this capability—those are separate product intents. Send a JSON object with three required finite numbers: efficacy, the published vaccine efficacy in percent on the closed interval from zero to one hundred; doses, a non-negative integer count of doses received, at most twenty; and months, the non-negative elapsed time in months since the last dose, at most six hundred, with fractional months allowed. Aliases such as vaccine_efficacy, ve, efficacy_pct, n_doses, doses_received, dose_count, shots, months_since_last_dose, months_since, elapsed_months, and time_months are accepted so forms and scripts do not need a single field name. Missing required fields, empty strings, non-finite values, non-integer doses, negative doses or months, doses above twenty, months above six hundred, and efficacy outside zero to one hundred all fail with invalid_input and a message that names the problem. On success the response returns remaining_percent as the primary estimate, echoes efficacy, doses, and months, and includes peak_percent, dose_factor, waning_factor, half_life_months equal to twelve, waning_rate_per_month equal to the natural log of two divided by twelve, primary_series_doses equal to two, and a formula string restating remaining_percent equals efficacy times min of one and doses over two times exp of minus ln two times months over twelve. Pair remaining_percent with your own schedule if you need to compare the educational estimate against a booster policy you chose yourself. Successful API calls cost the published $0.002 per item; validation failures never consume prepaid balance.

Where teams use it and how pricing works

Public-health explainers, immunization dashboards, and journalism notebooks use a vaccine immunity calculator to show how remaining protection falls after the last dose without reinventing exponential-waning code in every client. Classroom epidemiology modules can fix efficacy and doses and sweep months to illustrate a twelve-month half-life without a spreadsheet cell that drifted when someone edited the rate. The interactive tool above runs free in the browser for exploratory checks. Source inputs and outputs are retained only for the documented retention window and are never used to train models. Research pipelines that log self-reported dose counts and last-dose ages can post many independent tasks—one per person and interval—and store remaining_percent next to the session for later analysis. Programmatic calls use the prepaid KIT balance per successful item; invalid input never consumes balance. Latency is dominated by the task handshake rather than by computation, which makes the endpoint suitable for form validation and batch reprocessing of historical immunization tables alike. Always present remaining_percent as an educational estimate from the fixed-waning definition; clinical decisions require qualified professionals, local schedules, and eligibility context this tool does not collect.