As shipments of swine flu vaccine continue to arrive in Natrona County, health officials have begun to expand the number of groups they plan to immunize at upcoming clinics.

Absences at Natrona County schools, meanwhile, have returned to normal levels after peaking roughly three weeks ago, a district official said Tuesday.

People under 65 with chronic health conditions will be eligible to receive the vaccine at two clinics scheduled for Thursday in Casper, according to the Casper-Natrona County Health Department. A separate clinic for babies is scheduled for Friday at the health department.

The first round of public clinics in Casper were only available to pregnant women, people between 2 and 24 years old, and infant caregivers. Those groups, which health officials consider to be at high risk from the H1N1 virus, will still be eligible for Thursday's clinics at Kelly Walsh high and Cottonwood elementary schools.

The health department has 1,100 doses for those clinics, said Special Operations Manager Audrey Gray. At last month's clinics, officials immunized just under 1,500 people before running out of the vaccine.

A similar situation is possible at the upcoming clinics, Gray said.

"It very well could happen again," she said.

Fewer health workers will be available for the next clinics, which might slow the distribution process, Gray said. During earlier clinics, people experienced hour-long waits.

"I ask for everybody's patience," she said. "We are doing what we can."

People can line up early, but Gray said they should stay outside of school buildings until directed inside by health workers.

Swine flu, while not any more severe than the seasonal influenza virus, affects young people at higher rates. That led to spike in absences last month in Natrona County schools.

Since then, absences in the Natrona County School District have returned to the normal rate of 3 percent to 5 percent, said Safe Schools Director Marty Wood.

"For us, it's good news," he said. "Hopefully, it came through and doesn't come back."

Last month, 14 public schools experienced days where at least 10 percent of their students stayed home. It's now been more than a week since a school was above that mark, according to Wood.

"As far as the school district, we are in a lot better shape than we were a few weeks ago," he said.

Health officials say Wyoming is experiencing widespread flu activity at higher levels than any recent flu season. Roughly 3,300 cases of influenza have been reported to the Wyoming Health Department since late May. More than 600 of those cases have been confirmed as swine flu.

The actual number of people infected by the H1N1 virus is likely much higher since most people don't seek treatment or get tested.

Reach reporter Joshua Wolfson at (307) 266-0582 or at josh.wolfson@trib.com. Visit tribtown.trib.com/JoshuaWolfson/blog to read his blog.

Upcoming swine flu vaccination clinics

Thursday's swine flu clinics will be held from 3:30 p.m. to 7 p.m. at Cottonwood Elementary School gymnasium and Kelly Walsh High School cafeteria. They will be open to:

* Pregnant women;

* People between 2 and 24 years old;

* Parents and daycare providers of children under 6 months;

* People between 25 and 64 with chronic health conditions (respiratory or heart problems, diabetes, kidney disease, compromised immune system).

Vaccines will be free. Children under 18 must be accompanied by a parent or legal guardian.

A clinic for babies will be held from 8 a.m. to 4 p.m. Friday at the Casper-Natrona County Health Department. Children between 6 months and 35 months are eligible.

Another public clinic is scheduled for Dec. 3 at Cottonwood and Kelly Walsh.

For more information, visit www.casperhealth.com.