Laura Brewster, healthy and fit at 56, ran, swam, and played tennis. Two weeks ago, she returned to Glenside from a dream vacation in China. Less than a week later, she was dead of swine flu.

Kevin Hirsch, 26, almost never missed a day of work at a McDonald's restaurant in Northeast Philadelphia. "He didn't have a runny nose, a cold, or a fever in 15 years," said his father, Mickey, who disconnected his son's life support on Nov. 18 after nearly 15 agonizing days in the ICU.

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For months, public health authorities have emphasized the dangers of swine flu for people with specific medical conditions. Such patients account for between 60 and 80 percent of hospitalizations and deaths.

But 20 to 40 percent do not fit that profile. Some may have gotten medical care too late. Some may have had underlying conditions not known to them or their doctors or factors, such as a genetic predisposition, that science has yet to discover. Others may simply have lost out in the roll of the dice, like the nonsmoker who dies of lung cancer.

As a society, we tend to think everything has a clear cause, said epidemiologist Laurie Kamimoto, who leads the U.S. Centers for Disease Control and Prevention's surveillance of influenza hospitalization.

"I don't think people cozy up to the idea that it [may be] just bad luck," she said.

Even as more people die from swine flu, new cases have dropped dramatically, a concern to experts who fear that people will skip vaccination, making them vulnerable to a return wave.

Scientists worldwide are trying to identify who is most at risk from novel H1N1 influenza. Children were identified early on. The biggest risk factors for seasonal flu - pulmonary, heart, and metabolic diseases (such as diabetes), and immune systems that are suppressed (by drugs for cancer and diseases such as HIV) - do raise the risk of complications from swine flu.

Pregnancy, another known risk, appears to be an even greater factor in this pandemic. Hypertension, a history of smoking, and obesity also may make people more vulnerable.

Morbidly obese people (body mass index of 40 and above), currently 5 percent of the U.S. population, were hospitalized at five times the expected rate, Kamimoto and colleagues reported in the New England Journal of Medicine last month. Most had other chronic conditions, however, so the reasons are unclear.

Brewster and Hirsch each had a slight brush with possible new risk factors: She smoked one or two cigarettes a day before quitting last year. He, at 5-foot-4 and 180 pounds, qualified as obese (defined as BMI of 30 and over; his was 30.9).

In interviews, however, their doctors and families described them as unusually healthy and at no particular risk of complications. They were not members of any group currently given priority for immunization, and they did not get vaccinated.

With vaccine supplies slowly increasing, the government is expected soon to expand eligibility. Reports this week that a swine-flu strain resistant to the antiviral Tamiflu was implicated in the death of a Delaware man last month, as in a handful of other cases worldwide, highlighted the role of vaccine as a key barrier to infection.

The death toll has continued to rise, now touching every county in the region except Bucks. Pennsylvania attributed 65 deaths to swine flu through yesterday, including one each in Chester and Delaware Counties, five in Montgomery, and at least 15 in Philadelphia. New Jersey listed 34 deaths through last week, including two each in Camden and Burlington Counties, and three in Gloucester County.

The actual death toll is widely believed to be far higher. The CDC yesterday estimated that nearly 10,000 people have died nationwide, about 10 times the number of confirmed cases. None were believed to have died during the normal flu season, which typically kills an estimated 36,000 Americans.

Meanwhile, new swine flu cases have plummeted.

Just 2.4 percent of specimens from a sampling of laboratories in the extended Philadelphia region tested positive for flu last week, said SDI Health L.L.C., a Plymouth Meeting company that analyzes health data. That is down from 30.1 percent six weeks earlier and close to the lowest recorded in a year for the region, which extends from Reading, Pa., east to Ocean City, N.J., north to Trenton, and south to Dover, Del.

Visits to the emergency room at Children's Hospital of Philadelphia, which hit a record in October, declined to normal levels about 10 days ago for the first time since September.

Less sickness may mean less interest in vaccine, and that worries Mickey Hirsch. In the three weeks since Kevin's death, he has turned grief into action.

The single father of three had a powerful bond with his preternaturally happy eldest son, who had a constellation of cognitive deficits, from severe learning disabilities to an inability to think abstractly, since infancy. "He didn't understand history, didn't understand God, but he understood sports," Hirsch said, "and he had a Ph.D. in public transportation."

Now the independent contractor is on a whirlwind campaign for vaccination, tacking more than 100 homemade posters around his Welsh Road-Willets Road neighborhood, and purposefully corresponding with thousands of people on the "Prayers for Kevin Hirsch" Facebook page set up during his son's illness.

For those who are uncertain, he offers support, personally escorting dozens to get vaccinated at the city health center on Cottman Avenue.

And for those who loudly question the worth or safety of vaccines, he is blunt: "They should be thankful that their parents didn't feel the same way when it came time to get the polio vaccine. Otherwise you would be on crutches or in wheelchairs."

Stanton Segal, medical director of Aria Health and an attending physician at its Torresdale Campus, where Kevin Hirsch died, is less strident. "It is a good illustration of how important it is to get vaccinated," he said. "This was a pretty healthy young guy."

In fact, researchers have noticed a paradox with this flu and others. "Some of the people in the most robust health," said Andrew T. Pavia, chief of pediatric infectious diseases at the University of Utah School of Medicine, "have the most severe disease."

One possibility is that their immune systems are so aggressive that they fail to shut down, overwhelming the body.

The trait may turn out to be genetic. A paper that Pavia coauthored last year in the Journal of Infectious Diseases found that the siblings, children, and grandchildren of people who died in the 1918 influenza pandemic were more likely than others to die of flu-related complications decades later.

Inherited or not, an immune system so strong that it can kill when provoked might be strong enough to confer unusually good health otherwise, Pavia said.

Such a scenario could help explain, in theory, cases like Laura Brewster's.

"She entered your life with the gusto of a Nike ad and challenged you to just do it," said Fran Duffy, rapidly tapping the words on a small laptop for a visitor at her home in Lafayette Hill.

The women's friendship began at a swimming pool more than 10 years ago; when Duffy later lost the ability to speak after a stroke, Brewster became a part-time caregiver. It was Brewster who suggested a 12-day adventure, Shanghai to Beijing, including the Great Wall, the terra cotta army of Xi'an, and a Yangtze River cruise.

On the last day, she developed a cough and figured it was a mild flu. It had worsened by the time she arrived home on Thanksgiving Day, her family said. Two days later, her doctor said her lungs seemed clear but he wrote prescriptions for medicine to ease her breathing, and for a chest X-ray.

"Oftentimes early on there can be no indication that things are going to get much worse," said Jaclyn Rosenzweig, an infectious-disease doctor at Abington Memorial Hospital who later consulted on the case. "On the other hand, if they sent everybody into the hospital who had influenza, the hospitals would be overwhelmed," she said, and all the mildly sick patients would spread disease.

On the Sunday after Thanksgiving, one day after seeing her doctor, Brewster went to Abington. By the next day, she was on life support. Two days later, on Wednesday, she died.

"She was the picture of health," Duffy wrote on her keyboard, "the most unlikely person" to die from swine flu.

"I would have thought I'd be more vulnerable."

For More Information

Public flu vaccine clinics

Eligibility varies from place to place; call ahead or check the Web site below. Some New Jersey Walgreens and Wal-Marts also offer vaccine for specific groups.

Philadelphia: Walk-in clinics six days a week at 28 locations around the city. Information: 215-685-6458.

Bucks County: 4 to 9 p.m. Monday at Central Bucks High School South and Tuesday at Pennsbury High School East. Information: 1-877-477-4492.

Chester County: Next week, by appointment. Reservations: 610-344-5353.

Montgomery County: 2 to 5 p.m. Tuesday at Franconia Mennonite Church in Telford and Thursday at the community college's phys-ed building in Blue Bell. Information: 610-278-5117.

Camden County: 10 a.m. to 2 p.m. today at Bellmawr Fire Hall. Information: 1-800-999-9045.

Gloucester County: 4 to 6 p.m. Thursday at the county Institute of Technology gym in Sewell. Information: 856-218-4141.

Memorial details

Kevin Hirsch: Contributions to the "Kevin Hirsch Memorial Fund" will go toward a vaccine-poster campaign, medical bills, and other purposes. Checks may be mailed to Box 1174, Forked River, N.J. 08731.

Laura Brewster: Friends may call 7 to 9 tonight at May Funeral Home, 354 Easton Rd., Glenside. A Funeral Mass will be 1 p.m. tomorrow at St. Vincent de Paul Church, 109 Price St., Philadelphia.

Links to memorial information and to public vaccine clinics throughout the region: http://go.philly.com/flu/

Inquirer staff writer Don Sapatkin will chat with readers about swine flu at noon today. EndText

Contact staff writer Don Sapatkin at 215-854-2617 or dsapatkin@phillynews.com.