Whooping cough vaccine's durability questioned

(09-21) 13:39 PDT SAN FRANCISCO -- The whooping cough vaccine given to children before they start school may lose its effectiveness at a faster pace than previously thought, leaving kids with dramatically reduced protection from the illness by age 8 or 9, according to a study of 15,000 Kaiser Permanente members in Marin County.

The research, which was unveiled at a medical conference in Chicago on Monday, bolsters California regulations launched this year requiring all middle and high school students to get whooping cough booster shots.

But it also suggests that public health officials may want to take an even more aggressive approach toward immunization and require kids to get boosters earlier, said Dr. David Witt, chief of infectious diseases at Kaiser Medical Center in San Rafael, who led the study.

"It raises the question of how durable the vaccine is," Witt said. "It's clearly effective in the age group most at risk, namely young children. But we found a collection of fully vaccinated older children who seemed to have a very high rate of disease, and they were children who were three or more years since their prior booster."

Public health experts have assumed that the childhood vaccine offered strong protection for at least seven years, which is why they recommend a booster shot for children entering middle school.

The results of the Kaiser study have not yet been published, and public health officials at the state and national level said they hadn't seen the data yet. Witt said the results of his research will need to be confirmed in a larger study.

"We do know immunity wanes over time, which reinforces the importance of booster shots," said Dr. Gilberto Chavez, chief deputy for the state's Center for Infectious Diseases in a statement.

Last year, California experienced its worst outbreak of whooping cough, also known as pertussis, in 50 years. More than 9,000 cases of the disease were reported statewide, and 10 infants died, all but one of them before they'd received their first dose of the whooping cough vaccine. This year, rates of whooping cough cases in California are much lower, and there have been no deaths so far.

Whooping cough, which gets its name from the sound some children make when they wheeze between coughing fits, is usually an annoying but fairly mild disease in adults and children. But it can be fatal in babies who haven't yet been vaccinated.

Children in California typically get five doses of whooping cough vaccine before starting kindergarten. In 2005, a booster of the vaccine became available for adults and children 10 years and older. But it wasn't until last year's outbreak that state public health officials started a campaign to encourage all older kids and adults to get boosters.

A newer, less potent version of the whooping cough vaccine has been widely used in the United States since the mid-1990s. It replaced an older version that had some serious side effects, including high fevers and, occasionally, seizures.

But the older vaccine may have been stronger than the current one, Witt said, which may explain why the newer vaccine's protection seems to fade after just a few years.

Witt said he started his study among Kaiser patients in Marin because the county is known for having some of the lowest childhood vaccination rates in the state. He wanted to see how much of an effect those low rates had on the rate of whooping cough disease in Marin.

While it was true that unvaccinated children were especially vulnerable to the disease, Witt said he was surprised to find that about 80 percent of the kids who were diagnosed with whooping cough had already been vaccinated.

"The bottom line is that it looks like after three years, the vaccine is roughly half as effective as it was in the first three years" after kids are vaccinated, Witt said.

This story has been corrected since it appeared in print.


E-mail Erin Allday at eallday@sfchronicle.com.

This article appeared on page C - 1 of the San Francisco Chronicle



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