But a few outbreaks of whooping cough, known medically as pertussis, have been reported around the country this year. By far the biggest is in California, where state health officials counted 3,076 confirmed and suspected cases through last Tuesday, a number seven times higher than the same period last year. Eight infants have died.
No one is known to have died in Southeastern Pennsylvania. But the potential danger to infants who have not yet developed immunity - the vaccine is given in a series of shots at months 2, 4, 6, and 15 to 18, with a booster at 4 to 6 years - prompted the state's announcement Monday.
Health researchers in recent years have discovered that pertussis is far more common than had been previously believed. Hundreds of thousands of Americans probably contract it every year, thinking they have a run-of-the-mill cough.
Babies, however, can become quite sick. About 25 or 30 infants in the United States die each year from pertussis, nearly all of them under 3 months old, said Paul A. Offit, chief of infectious diseases at Children's Hospital of Philadelphia.
While many infectious diseases, notably the flu, spread quickly among children who then infect adults in the household, Offit said, pertussis infection occurs differently: Older children and adults get infected, usually are never diagnosed, and then transmit the disease to infants.
No pertussis vaccine offers more than a decade or so of full protection, he said, which is why the Centers for Disease Control and Protection several years ago recommended a booster shot at ages 11 to 12. Philadelphia last year began requiring that booster for entry into sixth grade, but many other jurisdictions haven't.
