Medical: Faltering vaccinations for pertussis, other kids' diseases?

How's your memory? Not your "do you remember what you had for lunch yesterday" or "where'd I leave my keys" memory, but your body's recall of infectious-disease challenges in the past -- otherwise known as immune function?

Depending on when and how you were vaccinated, your immune response may not be so good.

There is growing evidence that vaccinations against several childhood diseases are not doing as well at protecting kids into their teens and young adulthood as public-health specialists had hoped.

The most pressing lapse appears to be immunity from pertussis or whooping cough, a once-common respiratory infection that's making its strongest comeback since the late 1950s, according to figures released by the federal Centers for Disease Control and Prevention in mid-July.

Babies are at greatest risk from the infection, which causes uncontrollable, violent coughing and frequent severe complications ranging from cracked ribs and pneumonia to death. (Nine babies have died from the disease in the United States so far this year.) But infants can't begin the vaccination series until they're at least 2 months old; their young immune systems simply can't respond until then. They don't achieve maximum protection until they get a fifth and final dose at ages 4 to 6 years.

That means the only way to protect babies is to keep people around them from getting pertussis and passing it along, making new moms and pregnant women the top targets for a booster vaccination, along with other caregivers and siblings. But only about 8 percent of adults have ever gotten the booster shot, surveys show.

Normally, a pertussis booster shot is recommended for kids around 11 or 12, with the expectation that immunity would endure into young adulthood. But that hasn't been happening in this year's outbreak, with a troubling number of the 18,000 pertussis cases reported to the CDC thus far occurring among 13- and 14-year-olds. Most had received the booster shot.

CDC officials say several factors besides waning immunity may be involved in the increase in cases among adolescents, including recent changes in the vaccine itself. Other research suggests that the duration of immune response has waned since 1997, when the U.S. stopped using a vaccine formula made from killed whole cells in favor of a vaccine that uses parts of cells (acellular) to reduce side effects such as fevers and injection-site swelling.

The situation is confusing, because until just in the past year or two, some children who got the acellular booster shots had also gotten doses of the whole-cell vaccine in baby shots. Long-term studies that showed pertussis immunity lasting 40 years or more were all based on people who either got the old vaccine or had been naturally infected, which conferred immunity.

Dr. Anne Schuchat, director of the CDC's National Center for Immunization and Respiratory Disease, said it appears the acellular vaccine is 95 percent effective once the childhood series is complete. But that immunity wanes to 70 percent within five years, which explains the slight increase in disease detected among 7- to 10-year-olds.

More studies are being done as officials try to figure out the timing and frequency of additional booster shots. In the meantime, Schuchat and others stress that even some immunity is better than none for limiting the spread and severity of whooping-cough cases.

Authorities also say they don't think refusals to vaccinate children on schedule or at all are responsible for the widespread outbreaks, although clusters of unvaccinated children have been shown to contribute to some pockets of disease and increased chances to spread infection.

Other diseases held in check by childhood shots have also broken out. A 2006 mumps outbreak in eight Midwest states roared through college campuses, even though 84 percent of the 18- to-24-year-olds who got sick had gotten the recommended two shots as toddlers and just before first grade. There have been similar outbreaks among the vaccinated in Australia and Canada. Researchers have been studying whether the vaccine can be made stronger, or if a booster shot in the late teens would be worthwhile.

Measles, once thought to have been all but eradicated by childhood vaccination, has also had some resurgence due to waning immunity and the absence of booster shots. Several studies suggest that sustained immunity has actually diminished as measles have become rare. The antibodies generated after baby shots decline if they don't occasionally confront the actual virus.

(Contact Scripps Howard News Service health and science writer Lee Bowman at BowmanL@shns.com .)