H1N1 swine flu can kill children at a much higher rate than seasonal flu, and the elevated risk for pregnant women extends as long as two weeks after they give birth, researchers reported on Wednesday.

The findings show that the H1N1 pandemic, while overall no more deadly than seasonal flu, is capable of hitting vulnerable women and children far harder than regular flu usually does.

Pediatric 2009 H1N1 influenza was associated with pediatric death rates that were 10 times the rates for seasonal influenza than in previous years, Dr. Romina Libster of Hospital Posadas in Buenos Aires and colleagues wrote in the New England Journal of Medicine.

They said hospitalization rates for children with H1N1 were twice those of the 2008 rate for seasonal influenza.

H1N1 flu has killed more than 10,000 people in the United States alone, infected nearly 50 million and put 200,000 into the hospital. Pregnant women and children were known to be at higher risk and had already been given priority for the vaccine.

The results show that prompt treatment is important, Dr. Fernando Pollack of Vanderbilt University in Tennessee said in a telephone interview. Roche AG's Tamiflu and GlaxoSmithKline's Relenza can help ease symptoms if given quickly.

We cannot chase this disease from behind. Once it gets going, it is very difficult to treat. All our fatal cases had not been treated within 48 hours of the development of symptoms, he said.

FOCUS ON BUENOS AIRES

Patients with lung problems or neurologic problems are at serious risk of not only having serious disease, but dying of swine flu, Pollack added. They should not only be targets for vaccination, but for treatment.

Of 251 children hospitalized with H1N1 at six pediatric centers in Buenos Aires through July, 19 percent ended up in the intensive care unit and most of them required mechanical ventilation.

The death rate was 5 percent. Nearly one third had no pre-existing health problems, and the risk was highest among children less than 1 year old.

In contrast, none of the youngsters hospitalized for seasonal influenza required intensive care.

A second study, involving 94 pregnant women who became ill with H1N1 before August 11 in California, found that those who delayed treatment were four times more likely to end up in the intensive care unit or die compared to those who received antiviral therapy no later than two days after symptoms appeared.

Although pregnant women frequently presented with mild or moderate symptoms, many had a rapid clinical progression and deterioration, Dr. Janice Louie of the California Department of Public Health and colleagues wrote.

Eight women who were hospitalized for H1N1 flu had given birth less than two weeks earlier, four required intensive care and two died, highlighting the continued high risk immediately after pregnancy, the researchers said.

That result was surprising, Louie said in a telephone interview. She did not know why women continue to be vulnerable after giving birth.

Tennessee Glaxosmithkline Medicine