IsItFluSeasonYet
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About

A straight answer to the question everyone asks when they feel sick.

IsItFluSeasonYet.com pulls weekly CDC surveillance data and translates it into one clear answer — is flu actually active right now, in your region — plus the timing guidance most sites never bother to give you.

What this site is

It's a flu activity tracker with a real answer at the top. Not "flu season typically runs October through May" — that's a Wikipedia sentence, not an answer. This site answers: is flu circulating right now, how bad is it, and what should you actually do about it today?

Below the yes/no answer you'll find the regional activity level, a recommendation on whether to test, whether vaccination still makes sense given where you are in the season, how this season compares to a typical year, and a full chart of the season arc so far.

Why we built it

The CDC publishes excellent flu surveillance data every week. Virtually no consumer-facing site surfaces it in a way that answers the question a normal person is actually asking. Medical sites tell you what flu is. Pharma sites try to sell you something. Local news runs "flu activity high in [state]" stories with no context or follow-through. None of them tell you whether to test today, or whether getting a flu shot this week is still worth it, or how many weeks are left in the season.

We built the site we wished existed — one that treats CDC data as the foundation of a useful tool, not a citation at the bottom of a listicle.

How the activity level is calculated

The core metric is weighted ILI% — the percentage of outpatient visits attributed to influenza-like illness, reported weekly through the CDC's ILINet surveillance network. ILINet collects data from thousands of sentinel providers across the country, making it the most reliable continuous measure of flu activity available in the US.

We map that percentage to a 0–5 scale calibrated against CDC historical thresholds. The CDC's national baseline is approximately 2.5% ILI; activity above that is considered elevated. The scale works as follows:

The displayed level is your HHS region's activity level when we know your location, or the national figure when we don't. National and regional data can diverge significantly — a bad season in the South may show Very High nationally while the Northeast is still at Low.

The timing engine — what makes this different

Raw activity levels tell you how bad flu is right now. What most people actually need is timing guidance — and that's what the sections below the hero are built around.

Should I test? shows a recommendation calibrated to the current activity level. At Moderate and above, antivirals like Tamiflu must be started within 48 hours of symptom onset to be effective — which means testing at the first sign of illness, not waiting to see if it gets worse. The site surfaces that urgency clearly when it matters.

Is it too late to vaccinate? uses the historical peak week for your HHS region and the two-week window for a flu shot to reach full effectiveness to calculate whether vaccination still makes meaningful sense this season. The answer changes week by week as the season progresses.

How does this season compare? benchmarks current ILI% against the CDC's 2.5% national baseline and shows whether this is a mild, typical, or heavy year — with a visual bar so the comparison is immediate.

Data sources

Flu activity data is pulled from the Delphi CMU Epidata API, which mirrors CDC FluView ILINet data in near-real-time. The API is free, requires no key, and provides national and regional ILI% figures for every week of every flu season going back to 1997. Clinical lab data — strain typing and test positivity — comes from the same source via the FluView Clinical dataset.

Data updates weekly, typically on Thursday, when the CDC publishes the prior week's surveillance report. The site displays the exact data-through date below the hero so you always know how fresh the numbers are.

Location is resolved via your browser's Geolocation API and reverse-geocoded through OpenStreetMap Nominatim. Coordinates are used only to determine your HHS region and are never stored or transmitted to our servers.

HHS regions — why flu data is regional, not local

The CDC tracks flu at the national level and across 10 Health and Human Services (HHS) regions. Unlike pollen, which varies meaningfully block-by-block, flu spreads at a regional scale — a strain moving through the Southeast affects all of Alabama and Georgia in roughly the same wave. City-level flu data simply doesn't exist in the surveillance network.

When you enter a location, the site maps your state to its HHS region and uses that region's ILI% for your activity level, vaccine timing, and test recommendation. The national chart and season comparison use national figures, which are available for the full season arc going back to week 40.

The weekly data lag

CDC FluView data always reflects the prior week — there is roughly a 7-day lag between real-world conditions and reported numbers. This is a property of the surveillance system, not a limitation of this site. The data-through date shown below the hero makes the vintage explicit so there's no confusion about what "current" means.

Clinical lab positivity — the share of flu tests coming back positive — updates on the same weekly cadence and is shown in Section I as an early-warning signal when it's rising ahead of the ILI numbers.

Who built this

This site is part of a small network of seasonal condition trackers built to answer the questions people actually type when they're trying to figure out what's happening outside — or inside their own bodies. The allergy counterpart is at isitallergyseasonyet.com. The mosquito tracker is at isitmosquitoseasonyet.com.

Editorial decisions — what to show, how to frame it, what thresholds to use — are made here, not by committee. If a threshold seems off for your region, or you have a question about how something works, the contact page goes directly to the person who built it.

We are not physicians, and nothing on this site is medical advice. For anything beyond general guidance, talk to your doctor. See our Terms for the full disclaimer.

Affiliate disclosure

Some product links — test kits, thermometers, humidifiers, masks, and hand sanitizer in the Essentials section and guides — are affiliate links. If you purchase through one of these links, we may earn a small commission at no additional cost to you. Products are selected because they're genuinely useful during flu season, not because of the commission rate.

Get in touch

Questions, data corrections, or feedback go to hello@isitfluseasonyet.com, or use the contact form.