Whooping Cough Vaccine: Does Its Effectiveness Wear Off Faster?

A new rise in whooping cough cases in California is raising questions among doctors about whether there are problems with the current vaccine. California public health data show a spike in whooping cough cases in 2013 compared to the year before, and last week officials confirmed the first death from the disease since the major outbreak of 2010: an infant in Riverside.

Whooping cough, or pertussis as it is referred to in medical circles, is cyclical in nature and tends to peak every three to five years. But doctors are now finding evidence that the new vaccine may start to wear off on a similar timeline, despite medical recommendations that allow for a span of eight years between booster shots.

“The efficacy of the new vaccine is really good, it works. It’s just that it wanes, and it wanes more quickly,” said Dr. Michael Witte, a pediatrician in Pt. Reyes, north of San Francisco.

The new acellular whooping cough vaccine was introduced in the 1990s. It has fewer side effects than the earlier whole-cell vaccine that had been in use since the 1940s. By 2001, the old vaccine was completely phased out. So while many adolescent kids have received boosters of the new vaccine, they would have gotten shots when they were babies that included the old vaccine.

Kids who are now between 11 and 15 years old -- the main group that is getting sick -- are the first generation to have received only the new vaccine. That is leading doctors treating them to conclude that immunity from the acellular vaccine starts to wear off after three years.

“Pertussis vaccines have never been that strong,” said Paul Katz, a pediatrician at Kaiser Permanente in San Rafael. “But the attempt at making vaccines safer has created a potential lapse in protection in older people.”

Dr. Katz’s recent research in Marin County shows that kids who have received had only the new vaccine are five times more likely to get whooping cough.

The current medical recommendation is for kids to get four whooping cough shots in the first two years of life, then a booster before kindergarten and another in middle school. That’s a span of up to eight years. Now doctors are talking about whether the recommendations need to be updated to account for the three year dip in the vaccine’s effectiveness.

“This phenomenon of waning immunity is just coming to the surface,” said Dr. James Watt, the chief of communicable disease control for the California Department of Public Health. He says the review of current recommendations has reached the Centers for Disease Control and Prevention.

“Folks at the national level are looking at information about the effectiveness of giving additional doses, whether there are issues with any local reactions associated with additional doses, things like that,” he said.

Dr. Katz and Dr. Witte agree that the root of both the 2010 and 2013 whooping cough outbreaks in Marin was a cluster of kids who had never been vaccinated. Marin has the highest rate of the disease of any county in California, according to public health data. Doctors believe those numbers are directly related to the county's comparatively high rate of parents  who declined to vaccinate their children.

“We had a lot of unvaccinated children that acted as the kindling to start an outbreak,” said Dr. Katz. “Those children were able to infect all the other children who were vaccinated but were too early for a booster – they became the rest of the wood to start the fire.”

A new state law that went into effect in January now requires families who refuse vaccines to talk to a health care provider about the risks and benefits of vaccines.

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