Experts have been warning for years about the small but growing number of people who decline or delay immunizing their children because they fear side effects or believe the diseases are gone.
Haemophilus influenzae type b, which is unrelated to the influenza known as the flu, used to infect 20,000 children under age 5 each year in the United States before vaccines were licensed for children 1987 and infants in 1990. About 1,000 died, and many of those who survived were left mentally retarded.
"It was just a horrible disease," said Caroline Johnson, director of the Philadelphia Health Department's Division of Disease Control.
Johnson's last personal encounter with Hib came during her medical training two decades ago. The city's last previous case was in 1997.
Recent epidemics of whooping cough and measles, two other vaccine-preventable diseases, also have been linked to lack of vaccination. Just yesterday, three measles cases were reported near Pittsburgh, bringing the state's total to four - already more than in any year since 2003. The fourth, a University of Pennsylvania student whose case was reported in February, was Philadelphia's first case since 2001.
The Hib situation is complicated by a vaccine shortage.
Merck & Co. Inc. announced in December 2007 that it was withdrawing 1.2 million doses of its vaccine because of possible contamination of its equipment in West Point, Pa.
Sanofi Pasteur, which makes another Hib vaccine at its plant in Swiftwater, Pa., increased production but could not completely make up for the shortfall.
Until vaccine is again fully available - Merck now expects manufacturing to be ramped up by mid- to late 2009, a spokeswoman said - the government has issued guidelines to conserve supplies.
