Flu season in Mid-Atlantic: The corridor from DC to Philadelphia sits right at the national average
The Mid-Atlantic is the most demographically varied HHS region in the country. On one end, Washington DC, Baltimore, and Philadelphia form one of the continent's densest urban corridors — Amtrak's Northeast Regional alone moves 30,000 people daily between these cities. On the other end, West Virginia is one of the most rural states in the country, with communities that can go weeks before flu arrives — and then get hit harder when it does, with fewer hospital beds to absorb the surge.
Current flu activity — HHS Region 3
This data is pulled live from the Delphi CMU Epidata API, which mirrors CDC FluView ILINet data for HHS Region 3. It reflects the most recent week available — typically data through the prior Saturday, published by the CDC the following Thursday.
States in HHS Region 3
HHS Region 3 covers Delaware, District of Columbia, Maryland, Pennsylvania, Virginia, and West Virginia. These states are grouped together by the Department of Health and Human Services for federal health program administration, and the CDC uses the same regional boundaries for flu surveillance reporting. ILI activity data is aggregated across all ILINet providers in the region, so the number reflects the regional average — individual states can vary significantly.
When flu typically peaks here
HHS Region 3 tracks closely with the national flu timeline. The typical peak falls in mid-January to early February, with the DC-Baltimore-Philadelphia corridor often showing the season's arrival a week or so before the rural interior. In early-season years, December activity in the urban core can signal a January peak; in late-season years, the peak can push into February across the whole region.
Pennsylvania's internal variation is notable. Philadelphia and Pittsburgh are distinct epidemiological units — Philly is tied to the NYC-DC transit corridor and often tracks with Region 2; Pittsburgh is more isolated, with flu arriving and peaking slightly later. The rural central Pennsylvania counties fall in between.
West Virginia consistently lags the rest of the region by one to two weeks, due to lower density and more limited inter-regional travel. The trade-off is that when flu does arrive, healthcare systems are under more strain relative to capacity.
What drives Mid-Atlantic flu patterns
The Amtrak Northeast Corridor. The stretch from DC to Philadelphia to New York is the most heavily traveled inter-city rail corridor in the Western Hemisphere. Every Acela and Regional train is a mixing event for respiratory viruses. Epidemiologists have mapped flu spread along this corridor in multiple seasons.
Federal workforce concentration in DC. The Washington metro area has one of the largest concentrations of government office workers in the country. Large agencies with dense cubicle environments and mandatory in-person work during flu season are efficient transmission environments. Virginia suburbs (Arlington, Fairfax, Loudoun) reflect DC flu patterns within days.
West Virginia's vulnerability. WV has the oldest median age of any US state and some of the highest rates of underlying health conditions that increase flu severity. Hospital capacity per capita is among the lowest in the region. A season that's "Moderate" by national ILI standards can produce outsized hospitalizations in WV relative to bed capacity.
College and university density in the corridor. University of Maryland, Georgetown, GWU, American, Penn, Temple, and dozens of smaller schools create January return-from-break amplification similar to what Boston sees in Region 1. The DC-Philly corridor densities make this effect significant.
Recent seasons in HHS Region 3
Regional peak timing and severity can vary substantially from the national picture. The table below shows Region 3-specific peak months and severity for recent seasons, based on CDC FluView regional ILI data.
| Season | Regional peak | Dominant strain | Severity | Notable |
|---|---|---|---|---|
| 2024–25 | January | H3N2 / H1N1 | High | Above-average; DC metro and Philly peaked early January |
| 2023–24 | January–February | H1N1 | Moderate | Moderate season; WV lagged corridor by ~2 weeks |
| 2022–23 | December–January | H3N2 | High | Early season; Philly and DC showed activity before Christmas |
| 2021–22 | February–March | H3N2 | High | Late, compressed season; WV hit harder per capita than corridor |
| 2019–20 | January | H1N1 | High | Strong season ended abruptly with COVID-19 interventions |
If you're in the DC-Baltimore-Philadelphia corridor and activity is rising, assume it's already in your workplace. The transit density in this corridor means flu spread has a 3–5 day lag from downtown to suburb — not 2–3 weeks like more rural areas. See current Region 3 activity. →
How to use this data
The live activity level above reflects the most recent week of CDC ILINet data for Region 3. There is always roughly a one-week lag between real-world conditions and published numbers — providers report weekly, the CDC publishes Thursdays, and this page reflects those numbers. During a rapidly rising season, treat the current level as a floor.
The ILI percentage is the share of outpatient visits attributed to influenza-like illness across all ILINet reporting providers in the region. It is not a case count and does not capture people who don't seek care. In regions with lower healthcare utilization rates (rural areas, communities with limited access), ILI percentages tend to understate true community activity.
For the most complete picture of the current season — including strain typing, lab positivity trends, and hospitalization data — the IsItFluSeasonYet homepage shows all of this in context. The regional activity shown here is the same data source as the homepage's region breakdown.