« Back to Article

Whooping cough vaccines help but aren't foolproof

Updated 3:50 pm, Monday, March 31, 2014


  • Sylvia Ojeh of El Sobrante reacts to a shot of Tdap vaccine that guards against tetanus, diphtheria and pertussis, or whooping cough, in San Francisco. Photo: Lance Iversen, The Chronicle


Larger | Smaller
Email This
Page 1 of 1

A statewide immunization effort seems to have curbed the epidemic of whooping cough that swept through California in 2010, but scientists will need to develop a stronger, more durable vaccine if they want to wipe out the illness altogether, infectious disease experts say.

Only 169 cases of whooping cough have been reported in California this year. That's a dramatic drop from the 733 cases reported in the same time period last year, and the 1,337 cases reported in the first six months of 2010.

That decrease is likely due in part to a major public health campaign that forced California high school and middle school students to get a whooping cough booster shot last year. Adults, especially those who were going to spend time with vulnerable, unvaccinated babies, also were encouraged to get revaccinated.

But whooping cough is known to be cyclic, surging every three to five years, and infectious disease experts say that without a better vaccine, the state is likely to see another uptick in cases.

"The vaccine we have is very good at protecting people, but the durability of it is not long enough to last over that five-year cycle," said Andrew Resignato, director of the San Francisco Immunization Coalition. "The vaccine wanes over time, and that leaves gaps. The disease finds a reservoir of people it can spread to."

Federal public health officials are studying how long the vaccine lasts - both the initial childhood version and the booster - and whether adults should get repeated immunizations to remain protected over their lifetime.

In the meantime, some doctors and public health officials recommend that people who plan to be around unvaccinated infants and who haven't had a booster shot in more than two or three years consider getting another shot. That recommendation would apply especially to expectant parents and grandparents of newborns, Resignato said.

High risk for infants

Whooping cough, also known as pertussis, can be fatal in infants, especially babies in their first three months who haven't yet been vaccinated. In adults and children, it is usually an annoying but fairly mild disease, marked by coldlike symptoms and, often, severe and prolonged coughing attacks. It gets its name from the sound some children make when they wheeze between coughing fits.

Since an adult version of the vaccine was made available in 2006, doctors have encouraged parents and others who will spend a lot of time around newborns to get a booster shot.

In 2010, California experienced its worst outbreak of whooping cough in roughly 50 years - 9,156 cases, compared to fewer than 2,000 cases in a typical year, according to the state Public Health Department. Eleven babies in California died of whooping cough that year; last year there were no deaths, and none have been reported this year.

The 2010 outbreak hit other parts of the United States, too. Federal and state public health officials recommended that everyone get the whooping cough booster shot, although they focused efforts on middle- and high-school students who had probably lost protection from their childhood vaccination.

"Based upon the studies we've done, it seems that if those teens had not been vaccinated, the impact of the outbreak would have been much worse," said Dr. Ken Purdy, a pediatric infectious disease expert with Kaiser Santa Clara. "A lot more infants would have gotten sick and potentially had bad outcomes."

Imperfect vaccine

The problem is that the pertussis vaccine isn't perfect. About a decade ago, the original vaccine was replaced by an updated version that causes fewer side effects, but is also less effective - some studies have shown that up to 20 percent of people who get the newer vaccine aren't protected by it.

Plus, the vaccine's effectiveness fades over time, and no one is sure how long it lasts. Infectious disease experts had initially thought it offered protection for about seven years, but at least one recent study, out of Kaiser Permanente in Marin County, found that the vaccine loses about half of its potency after three years.

Even people who have actually had whooping cough aren't immune from becoming re-infected years later and need a booster shot to stay protected.

"Pertussis is a tough bacterium, and it's tricky," Resignato said. "For some reason the disease doesn't stimulate enough immune memory, so your immune system forgets how to fight it. That's the problem trying to make a vaccine that's really going to contain the disease."
