California pertussis epidemic may be caused by vaccine refusal

by John Gever

California is facing what could be the state’s biggest outbreak of pertussis since 1958, its top public health official said.

“Whooping cough is now an epidemic in California,” said Mark Horton, MD, MSPH, director of the California Department of Public Health, in a statement. “Children should be vaccinated against the disease and parents, family members and caregivers of infants need a booster shot.”

As of June 15, 910 cases had been confirmed in the state. Another 600 suspected cases are currently being investigated by local health officials, the statement indicated.

The number of pertussis cases is now on a pace to surpass the total of 3,182 seen in the most recent major outbreak, which occurred in 2005, said Ken August, spokesman for the department.

August told MedPage Today that 1,200 cases were recorded in 2005 as of mid-June, meaning the state would probably exceed that this year.

The highest yearly total on record is 3,837 cases, seen in 1958.

So far this year, five children have died, all infants younger than three months.

Blaise Congeni, MD, of Akron Children’s Hospital in Ohio, said he wasn’t surprised, as higher-than-usual numbers of pertussis cases have been reported across the country.

“We are having an outbreak in Ohio,” though not as severe as in California, he said in a phone interview.

Oregon public health officials have also reported an unusually high number of pertussis cases in that state.

Both Congeni and August noted that pertussis tends to wax and wane in cycles. But gaps in vaccination coverage may also be playing a role, particularly in California.

“California is the epicenter of vaccine refusal” in the U.S., said Congeni.

Although outright refusal as well as so-called designer schedules for vaccinations that deviate from evidence-based recommendations are occurring throughout the country, including Ohio, “it’s not as much as what my colleagues in California tell me,” Congeni said.

August explained that California requires that children receive the full slate of vaccinations for pertussis, measles, and other infectious diseases before they can attend school. But the requirement is waived if parents file a “personal belief exemption” (PBE), which need not be based on religion or medical necessity.

He said that the overall rate for PBEs among the state’s roughly 7,200 schools is about 2%.

But rates are much higher in some schools. Records for 2009 indicated that close to 175 schools had PBE rates of 20% or more. A few had rates above 70%.

Researchers have found that vaccination rates of at least 93% are needed to ensure so-called herd immunity against pertussis, which prevents the disease from spreading quickly to unvaccinated individuals.

However, August said that some parents may use the PBE to withhold just one vaccine from their children. Others may change their minds after filing a PBE and have their children fully vaccinated.

He also noted that, in severe outbreaks of vaccine-preventable diseases, local school officials can declare a health emergency and require that all schoolchildren be vaccinated. Parents who insist on withholding vaccination must then keep their children out of school.

August said he was unaware of any such declarations in the face of the current pertussis outbreak.

The California public health department first warned of a pertussis spike in April, when the case count was running double the rate seen at the same time in 2009.

The current outbreak in California still pales against a major epidemic that swept England and Wales in the late 1970s and early 1980s, after pertussis vaccination coverage dropped to 30% in the wake of controversy over alleged vaccine reactions.

From January to September 1982, for example, nearly 50,000 children and adults contracted the disease. As many cases were reported in a single week as are expected in California for the entire year in 2010.

John Gever is a MedPage Today Senior Editor.

Originally published in MedPage Today. Visit for more infectious disease news.

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  • Nemo

    How many of those diagnosed with pertussis were vacinated?

    The infants under 3-months who’ve died are tragic, but they were too young to be vaccinated and are at risk in any state since pertussis hasn’t been ‘wiped out’ anywhere, even with vaccination rates over 93%.

    • EA

      The point is that the risk of contracting the disease (for infants, immunosuppressed, etc) becomes much lower when the rest of the population is vaccinated. If the vaccination rates were higher, perhaps these infants wouldn’t have died.

      • Nemo

        The fact is that the vast majority of pertussis in the US is adults, with waning immunity, not children being unvaccinated. 53% of pertussis cases are in adults 19+ who were vacciinated; 40% of cases are in those 10-19, the vast majority vaccinated; the remaining 7% are in those under 9 with 93% vaccinated. Of the 7% that are unvaccinated, 95% are infants under 4-months are cannot be vaccinated!

        • bw

          I’d agree with that assessment, except that if an adult has waning immunity due to a lack of boosters, I am not sure that they are properly classified as being “vaccinated”. I think some would try to miscontrue this word to attempt to create evidence that the immunization was ineffective, when, in fact, the waning immunity was an anticipated result with booster shots available. I think that the interesting question will be, how many of these people had received their booster shot in the recommended period of time? Otherwise, they are susceptible to varying degrees and are liable to spread it just as someone who has not ever been vaccinated against pertussis.
          I will agree with you, though you have not suggested it, that there should perhaps be a greater effort to maintain immunity in aging populations and that they contribute to the loss of herd immunity as much as someone who has not ever been vaccinated. I do not know if that is your point, but I think that it is a valid one.

          • Nemo

            The biggest issue is that the booster only started to make headlines in 2005, and was only starting to be recommended in 2008. There has been no significant public appeal in or out of the medical community to have teens and adults get a booster!

        • EA

          Agree with bw. The point is that the Tdap is now a booster that is available for adults. The #1 recommendation to prevent infants and immunosuppressed from getting sick, is to vaccinate those around them, including kids and adults (through boosters). If more adults had gotten the booster and more kids had been primarily vaccinated, these kids may not have died.

          • ab

            1. my 3.5yo vaccinated child was sent for pertussis and Pneumonia tests yesterday here in California. Pediatrician explained that he is not responding to other treatments and that vaccinated children have been seen with this disease.
            => vaccinations may not prevent pertussis — I did not know this.

            2. In California, are adults in professional positions with contact with children, such as daycare centers, preschools, and schools, required to have vaccinations?

            3. Are schools required to report infections to others in the school, or only to public health administrators?

            4. Is there a correlation between detected infections and the population being vaccinated, for pertussis?
            Is the DTaP or Tdap booster, shown to be effective in areas where the population is nearly all vaccinated?

  • DO Student Doc

    It will be interesting if insurance companies start refusing care for vaccine-preventable conditions for folks who refused the vaccination.

  • DVM

    >>It will be interesting if insurance companies start refusing care for vaccine-preventable conditions for folks who refused the vaccination.>>

    Don’t think so, as this is analogous to insurance companies not paying for treatment of diabetes in the obese or emphysema in smokers.

    Appreciate the sentiment behind the thought, though.

  • sara

    Well, since adults and teens have not been historically vaccinated,how can adults and teens (who have always been carriers) suddenly be the cause of an ‘outbreak’? The increase in numbers is largely due to the fact that the medical establishment is finally admitting that pertussis vaccination does not produce life-long immunity and so now any adult/teen coming in with a cough is being diagnosed with pertussis – instead of allergies, irritation, etc. During the two year period 2001-2003, 51 infants under six months died from pertussis
    We are no where near this 25 death per year number now. The point being, there is no increase in pertussis deaths at all – just a whole lot more diagnosing of the older population.

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