Tamiflu is flying off the shelves in Chattanooga -- so much so that the city has topped national rankings for the highest level of flu activity in a metro area, data from the pharmacy chain Walgreens shows.

The data is based on the rates of prescriptions filled for antiviral flu drugs like Tamiflu and Relenza. The demand for such drugs is not likely to slow down soon as school ramps back up and peak flu season arrives, compounded by the fact that this year's vaccine has proven to be less effective.

In Tennessee, three children died of flu in December -- the highest number reported for that month since the state's health department began tracking them in 2007.

TOP CITIES FOR FLU ACTIVITY Week beginning Dec. 29, 2014



1. Chattanooga



2. Paducah, Ky. Cape Girardeau, Mo. Harrisburg, Ill.



3. Dallas-Fort Worth, Texas



4. Knoxville



5. Nashville



6. Tri-Cities, Tenn.-Va.



7. Columbia, S.C.



8. Oklahoma City, Okla.



9. Rockford, Ill.



10. Austin, Texas



Source: Walgreens Flu Index

The U.S. Centers for Disease Control and Prevention has listed Tennessee as one of 36 states experiencing "widespread" flu activity, but Walgreens officials say the company's data, which is released weekly, can provide a more detailed look at flu's spread.

Walgreens compiles the rankings from weekly retail data for Tamiflu prescriptions per store, explained company spokesman Jim Cohn. Researchers then account for factors like population and number of stores to gauge the demand for the drugs on a per-store average basis.

Based on those measurements, Chattanooga had the highest average of prescriptions per store.

"The objective was to drill down to the market level so we have hyperlocal information," Cohn said. "What's happening across the state could be very different from Western Tennessee to Eastern Tennessee."

And East Tennessee is seeing plenty of activity. Chattanooga was joined on the national Top 10 list by other Tennessee cities: Knoxville, Nashville and Tri-Cities. Tennessee is ranked third-highest for flu activity, according to the list.

In data that will be published on Tuesday, Chattanooga will fall to No. 3 on the national list, Cohn said.

The data show that Chattanooga also saw the biggest spike in flu activity in a short span of time. The surge tracks with what has occurred at the Erlanger Health System emergency room, which saw a jump from 115 flu patients during the week ending Dec. 20, to 212 during the week ending Dec. 27. The most flu cases the hospital saw in a one-week period last year was 76.

"Erlanger never even had one week with flu cases reaching the hundreds last flu season," said hospital spokeswoman Pat Charles.

From Oct. 1 to Dec. 18, Parkridge Medical Center and Parkridge East had treated 459 total flu cases. By Friday, that total more than doubled to 992 cases, hospital spokeswoman Alison Sexter said.

Chattanooga Hamilton County Health Department RN Brad Erwin fills a syringe with flu vaccine in the agency's immunization and travel clinic in Chattanooga while health department employee Jennifer Gillespie awaits her first-ever flu shot.

But while numbers appear to be surging within the past few weeks, Chattanooga health officials say this year's flu season so far is tracking with trends they have seen in the past.

"We're seeing a lot of flu activity, but it's not significantly higher," said Bev Fulbright, epidemiology manager at the Chattanooga-Hamilton County Health Department. "Outpatient visits for flulike visits have been up the last few weeks and continue to climb. There's no question -- we're in the thick of it."

Fulbright also said the Walgreens data may indicate that Chattanooga doctors and health officials have been more heavily promoting the need for antiviral drug Tamiflu.

This year's flu vaccine has been shown to be less effective than in years past because one of the strains included, H3N2, mutated beyond what researchers and drugmakers planned for.

But Fulbright and other health officials still stress that being vaccinated is better than not, as the vaccine can still protect against other flu strains. And doctors are still stressing that it's not too late to get the shot.

Contact staff writer Kate Belz at kbelz@timesfreepress.com or 423-757-6673.