MONDAY, June 29 (HealthDay News) -- With a worldwide pandemic under way and more than a million Americans sickened by the new swine flu, the special nature of this disease is becoming better understood.
Several articles published online Monday by the New England Journal of Medicine show that, unlike seasonal flu, the new H1N1 flu strain attacks younger people and can be more severe and deadly in that group. The reports suggest a possible vaccination policy and also account for some reasons that this strain of flu appears milder than that of other pandemics.
"These findings are in keeping with the fact that new strains or pandemic strains tend to be more deadly in younger patients," said flu expert Dr. Marc Siegel, an associate professor of medicine at New York University's Langone Medical Center in New York City.
Also Monday, health officials in Denmark reported what is believed to be the first case of someone with a strain of swine flu that's resistant to Tamiflu, an antiviral medication.
Though the H1N1 flu has been mild for most people, some have developed pneumonia and respiratory distress, which can be severe and even fatal. Most such cases have been confined to young and middle-aged people, many of them otherwise healthy.
One report targeted the initial flu outbreak in Mexico, which included 2,155 cases of swine flu reported by the end of April. Researchers focused on the 100 people who died and what caused those deaths.
They found that 87 percent of the deaths and 71 percent of the cases of pneumonia were seen in people aged 5 to 59 years. That's unlike what is seen with seasonal flu epidemics, in which, on average, 17 percent of those in that age range who are seriously ill die and 32 percent develop severe pneumonia.
The findings are similar to other flu pandemics, which have affected mostly younger people, the researchers said. Older people have some protection from the H1N1 strain because they have been exposed to earlier strains of H1N1 flu in childhood, specifically before the 1957 flu pandemic.
Given this, the researchers say, younger people should be vaccinated first when a vaccine becomes available, particularly if it is in limited supply, because they are most likely to get and spread the disease.
In another report in the journal, Mexican researchers also looked at the age distribution of those who died or developed acute respiratory distress from the new H1N1 flu. Of the 18 people with pneumonia hospitalized in April with the flu at the National Institute of Respiratory Diseases in Mexico City, more than half were 13 to 47 years old and only eight had a preexisting condition, the researchers found.
"The main finding is the capability of H1N1 of producing severe damage to previously healthy individuals," said the study's lead researcher, Dr. Rogelio Perez-Padilla, from the Mexico City institute. "Of course, some of the patients who died had chronic diseases, and they are in a higher risk, but the virus may affect healthy people," he said.
"Do not disregard the epidemic as mild or irrelevant," Perez-Padilla urged. "This has not been the case for an increasing number of individuals with severe disease and may change with time. Even for patients with severe disease there is hope, but unfortunately, we have to expect deaths in previously healthy individuals."