Karen Williams had tried to get her twins, Liam and Declan, immunized against the swine flu virus as soon as they were old enough, but a Burlington County clinic in November was postponed for lack of the vaccine.

So yesterday, Williams arrived with her 8-month-old boys an hour before the clinic opened at the Burlington Center Mall. They were numbers 47 and 48 in line, and they got the vaccine after less than an hour's wait.

That was very different from early November, when hundreds of people began lining up at 8:30 a.m. for a 2 p.m. clinic in Westampton. Seven hundred people were vaccinated that Friday, and 500 were turned away with tickets for a later date.

With vaccine becoming more widely available and the general public eligible, dozens of free clinics are scheduled throughout the region in the next few weeks.

And with swine flu almost completely gone, at least for the moment, health officials' concerns seem to be shifting. Rather than fretting over inadequate supplies of vaccine, they are worrying that there might be too little public demand.

Nearly 300 people showed up at Burlington County's two clinics yesterday. The lower numbers could reflect earlier successes in vaccinating highest-risk groups through public-health clinics, schools, and doctors' offices. But they could also reflect a lack of interest.

The Pennsylvania Department of Health, anticipating a third wave of swine flu this winter or spring, is airing public-service announcements to encourage immunization.

"You might wonder, Do I need the novel H1N1 flu vaccine?" Stephen Ostroff, the state's acting physician general, asks in one spot broadcast this week.

Ostroff answers his own question: Pregnant women, yes. Infant caregivers, yes. Aged 6 months to 24 years, yes. Chronically ill and under 65, yes.

Around the country, demand for the vaccine has varied from place to place, partly because disease outbreaks have not been uniform.

"We definitely are worried about people becoming complacent and thinking that this is all over," Tom Skinner, a spokesman for the Centers for Disease Control and Prevention, said yesterday. "We could very easily experience a surge in [flu] activity after the new year when schools are back in session."

About 120 million doses of the swine flu vaccine have been allocated to the states, and most have been distributed to providers, Skinner said. That is more than the 114 million doses of seasonal flu vaccine that manufacturers shipped earlier this year, he said.

In Pennsylvania, about four million doses of the swine flu vaccine have been distributed to 2,405 providers, which include private doctors, school districts, county health departments, and the state's own clinics. New Jersey providers have received about 2.4 million doses.

"I think people still want the vaccine," said David Damsker, director of the Bucks County Health Department, which immunized more than 40,000 schoolchildren before Thanksgiving and 20,000 additional county residents in three big free clinics earlier this month. Three more have been scheduled for next month.

"I expect to have several thousand people at these clinics in early January," he said, adding that he still fields about a dozen calls a day about swine flu vaccine, many from elderly residents who were not eligible until recently.

The Philadelphia Department of Public Health has vaccinated far more at dozens of clinics it has been running six days a week and will continue for at least another month.

Gloucester County has administered about 11,000 doses in several public-health clinics and has scheduled more than a dozen more for January, spokeswoman Debra Sellitto said.

Last night, 168 people came during the first hour of a clinic in Clayton, she said, somewhat fewer than anticipated.

At the Burlington Center Mall earlier in the day, Williams brought her twins early just in case.

"I was dreading it because I'd heard about the long waits," she said.

Still the 28-year-old stay-at-home mother from Moorestown braved the blustery weather because she wanted be sure her family was protected from the new strain of flu virus that has hit the young, pregnant women, and those with weakened immune systems particularly hard.

"They did a great job," she said of the county health workers and volunteers who ran yesterday's clinic. She had already received the novel H1N1 vaccine, as had her husband, Brendan, and 2-year-old daughter, Abigail. The twins were ineligible until reaching 6 months of age.

The county's two clinics yesterday and today were for people in specific groups. With vaccine supplies now plentiful, several clinics in January are open to all county residents.

"We would like to see more people come out," said William Weisgarber, Burlington County's program manager for disease prevention and control.

Weisgarber said that many of the children yesterday were in for their second dose. Two doses, about a month apart, are recommended for children under age 10 to build a robust immune response; everyone else gets a single dose.

Shelley and Keith Johnson and their five children all traveled to the Burlington Center Mall from their home in Laurel Springs for the vaccine yesterday.

"I'm a nurse, and I have seen too many people sick" with the flu, Shelley Johnson said.

"We were hunting for the shots," she said. "I didn't want to see them sick."

More Swine Flu Clinics Set

Most public-health clinics are free but limited to county residents.

Many are open to the general public, but some are still restricted* to specific priority groups.

Call ahead or check the Web site below for details.

Public clinics in Pennsylvania

Philadelphia: Dozens of walk-in clinics around the city

are open to the general public daily except Sundays and holidays through January.

Information: 215-685-6458.

Bucks County: Walk-in clinics in Perkasie and Langhorne on Jan. 14 and in Newtown on Jan. 15 are open to the general public.

Information: 1-877-477-4492.

Chester County: Clinics* are by appointment on Jan. 8 and Jan. 9 in West Chester.

Reservations: 610-344-5353.

Delaware County: Clinics run by the state health department are open to the general public, by appointment only, Jan. 8 and Jan. 9 in both Media and Chester. Reservations: 1-877-724-3258.

Montgomery County: Walk-in clinics Jan. 8 in Lansdale and Jan. 9 in Plymouth Meeting are open to the general public. Information: 610-278-5117.

Public clinics in New Jersey

Burlington County: Walk-in clinics* today at the Burlington Center and Moorestown Malls, with different restrictions at each. More than a dozen more clinics, some for the general public, are scheduled Jan. 5 through Jan. 18.

Information: 609-265-5548.

Camden County:** Walk-in clinics at five sites around the county Jan 5 through Jan. 14 are open to the general public. Information: 1-800-999-9045.

Gloucester County:** Walk-in clinics at more than a dozen sites around the county Jan. 6 through Jan. 26 are open to the general public.

Information: 856-218-4141.

* Eligibility restrictions vary widely from county to county and sometimes from day to day. Call ahead or check the Web site below for details.

** Separate vaccines against swine flu and seasonal flu will be available, although not necessarily during the same visit.

Details on all the above clinics are posted at http://go.philly.com/flu