NEW ORLEANS — Children with the blood condition known as sickle cell disease face an unusually high risk from infection by the H1N1 flu virus, scientists reported December 6 at a meeting of the American Society of Hematology.
In addition to fighting an ongoing battle with anemia, children with sickle cell disease have been shown to be 56 times more likely than other kids to be hospitalized for the seasonal flu, said hematologist John Strouse of the Johns Hopkins Children’s Center in Baltimore. In the new study, Strouse and his colleagues found that this risk may be even greater with the H1N1 strain of influenza.
Sickle cell disease is a hereditary condition in which red blood cells deform into a telltale crescent shape, thwarting circulation through capillaries and causing anemia, organ damage, pain and other problems. About 72,000 people in the United States have the condition.
Scientists analyzed the records of 118 children under age 18 who have sickle cell disease and were treated for flu from September 1993 to November 2009 at JHCC. The children were given antiviral flu medicines and their strain of flu virus was analyzed while they were kept under observation. Of these, 28 had H1N1 flu diagnosed in 2009 and 90 had a seasonal flu virus.
Nine of the 28 children with H1N1 developed a severe flu complication in which the lungs become inflamed, oxygen transport by the blood is impaired and the lungs become susceptible to opportunistic infections. This rate was three times greater than the rate for their counterparts who had seasonal flu, said Strouse, who presented the findings.
Also, a substantially greater percentage of children with H1N1 were placed in the intensive care unit, needed to get a blood transfusion, or were placed on a mechanical ventilator to breathe — compared with kids who had the seasonal flu.
Curiously, three patients with H1N1 had been previously vaccinated for the virus, Strouse said. But each had gotten a single dose, even though young children typically need two doses for full protection. Also, the children might have been exposed to the virus before getting vaccinated, he said.
Despite the high flu risk that children with sickle cell disease have, Strouse says, only about one-fifth get vaccinated against it each year, according to earlier findings. That number is borne out by several studies in the past decade that have found low rates of flu vaccination among children with various chronic diseases — a group that includes sickle cell disease.
Physicians need to emphasize the value of childhood vaccination when they counsel parents, particularly parents who have an at-risk child, said Alexis Thompson, a pediatric hematologist at Northwestern University Feinberg School of Medicine in Chicago. “In populations that are going to have the most difficulty with the flu — that’s where there is a need for providers to rethink how they approach these patients.”
Widespread vaccination begets what scientists call “herd immunity” as the intensity of a disease wanes with fewer unvaccinated people to infect. “There is something to be said for the benefits of herd immunity,” but it’s not foolproof, Thompson said. She acknowledged that many families, even those with at-risk children, just avoid vaccines. There’s a risk “if they opt out and hope that the children sitting next to them got vaccinated,” she said.
It remains unclear why H1N1 might be more dangerous for sickle cell children than seasonal flu seems to be. “Clearly, there is some increased virulence here,” Strouse said.