The California pertussis outbreak of 2010

If you haven’t already heard, California is in the midst of a major outbreak of pertussis (whooping cough). The California Department of Public Health is predicting that this could be the biggest outbreak in 50 years.

Here is a graph from the CDC ( via the LA Times ) which shows the number of pertussis cases in the entire US as a function of time up to and including the 2004/5 outbreak:

That was not just the sort of cyclic bump seen every 4-5 years even with vaccines. That was a big outbreak. And, now, California is set to see an even bigger outbreak.

So far 7 infants have died. They were too young to be vaccinated. What is especially troublesome is that usually the worst part of the year starts in August. Here is a figure from the CDPH comparing this year to last year:

By this time last year, no children had died.

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Dr. Snyderman is an “unabashed advocate” for vaccines and points out that people who selectively undervaccinate put people like the immune compromised and the very young at risk.

Barbara Loe Fisher of NVIC defended her group’s positions even before the MSNBC spot aired:

After watching the NVIC video I had a lot of questions. I posed a few of them to the California Department of Public Health. I appreciate them taking the time to reply:

NVIC states that there are outbreaks every 4-5 years and that “this is nothing new”. I asked CDPH:

There is an outbreak every 4 to 5 years (implying this is no big deal). I think this is correct as far as it goes, but the magnitude of this outbreak appears to be large. Is there public data on the size of previous outbreaks to compare this one to? I realize that will likely involve an estimate of the size of this year’s outbreak.

Yes, historically, there are “peak years” for pertussis every 3-5 years. This was true for other vaccine preventable diseases as well before they were controlled by vaccination. This is because once a disease sweeps through a population it takes at least a few years for adequate numbers of susceptible people to accumulate again in the population to allow sustained, widespread transmission of the disease. What is different about pertussis than other vaccine-preventable diseases such as measles, is that, unlike measles, neither pertussis vaccine or disease confers lifelong immunity. Pertussis susceptible people accumulate in the population via birth cohorts who are too young to be vaccinated, people whose immunity from vaccine or disease has waned, and people who are eligible to be vaccinated, but are unvaccinated.

The last peak year for pertussis in the U.S., including California was in 2005. This was a nationwide peak year with over 25,000 cases in the U.S, the most cases in 45 years, and over 3,000 cases in California, including 8 deaths. Although Tdap was first licensed in June 2005, not many people received it that year and it did not have an effect on the outbreak. We now have Tdap to use as a control measure that was not available in other peak years. Therefore, we are trying to increase the level of pertussis immunity in the population by encouraging the use of Tdap, particularly in people who have contact with infants.

California is having a peak year/epidemic in 2010. If current trends persist, there will be more cases in California this year than in 2005 and more cases than in 52 years ( see attached document, which has been released to the public ). Although some other states are reporting increases this year, no state has reported an increase similar to that seen in California, which has now had a six-fold increase from the numbers reported during the same time period in 2009, a non-peak year.

NVIC seems to be implying that parapertussis is the cause of the outbreak and that is not covered by the vaccine. Aren’t many cases, especially those hospitalized or the deaths, confirmed by PCR?

Parapertussis is also circulating and pertussis vaccine does not provide protection against parapertussis. However, we do not think parapertussis is the cause of our epidemic because most of the reported pertussis cases in California are laboratory confirmed to be pertussis. In addition, parapertussis does not kill healthy young infants. Tragically, there have been seven infant deaths in Calfornia this year, all of whom had laboratory confirmed pertussis.

NVIC is also claiming that B. Pertussis may be mutating away from the vaccine strain, so the vaccine would be failing. Besides being at odds with her own assertion that the outbreak is due to parapertussis, is there evidence for this? Are the outbreaks in unvaccinated individuals? The comparison is, of course, most valid in the very young, where immunity will not have had the chance to wane.

We are not aware of any evidence that the currently circuclating strains of pertussis are not covered by the vaccine. Of the reported cases for whom we have vaccination information, most were unvaccinated or undervaccinated. None of the seven infants <3 months of age who died had received any pertussis-containing vaccines.

I have a lot more questions and there is much to deconstruct in the NVIC and TACA statements, but this is not the time for that.

Is the current outbreak due to the activities of groups like NVIC, TACA and the Age of Autism? Let me put it another way since accusations bring on such strong reactions from these groups: does it matter right now if they are at fault? People are dying. The goal right now is to minimize suffering and death. Vaccines do offer protection and could limit this outbreak.