Filed at 1:58 p.m. ET

MONTPELIER, Vt. (AP) -- High demand for a new vaccine against childhood pneumonia, meningitis and ear infections has led to a shortage around the country.

The shortage of Prevnar should ease by the end of March, said its maker, Wyeth-Ayerst Laboratories.

Meanwhile, doctors are directing the supplies they do have to children who run the highest risk of infection, such as those with sickle cell anemia, the AIDS virus or other diseases that undermine the immune system.

``We've got it. We just don't have a lot of it,'' said Dr. Joe Hagan, a pediatrician in South Burlington.

Prevnar fights the bacterium streptococcus pneumoniae, the leading cause of pneumonia, meningitis and millions of ear infections every year in children.

According to the Food and Drug Administration, U.S. children under 5 suffer 16,000 pneumococcal blood infections and 1,400 pneumococcal meningitis cases every year. And until Prevnar, there has been no way to prevent them. In up to half the cases of meningitis, children suffer brain damage or hearing loss. About 10 percent die.

Prevnar was approved by the FDA two years ago. In June, a government advisory committee recommended that all children under 2 receive the vaccine.

Demand soared, far exceeding the expectations of Wyeth-Ayerst, said drug company spokesman Douglas Petkus, who estimates that 90 percent of infants in the United States have now received the vaccine.

``Physicians are using it at an incredible rate,'' he said.

At the same time, Petkus said, Wyeth-Ayerst made changes at the Pearl River, N.Y., factory where the vaccine is made that slowed production.

Hagan said pediatricians are being told to delay the booster shot that children usually receive when they are a year old.

``That makes sense, and it's safe,'' he said. ``If we immunize your baby at 2, 4, and 6 months, that immunity will last certainly past a year. If we don't give the 12-month dose until 18 months or 24 months, the children are still well protected.''