Thursday, July 8, 2010

The Rhetoric about the Pertussis Epidemic

A few weeks ago, an epidemic of whooping cough (Pertussis) was declared in California. As of June 30th, five infants have died and a total of 1,337 cases have been confirmed. The majority of these cases (89%) have been in infants less than six months old. As the number of cases is well over the number of cases that had been seen at this time last year in California (258), an epidemic was declared and health authorities are actively trying to encourage vaccination in an effort to curtail the spread.

First let me say that the death or illness of any child, especially when it could have been prevented, is a tragedy and my heart goes out to those families that have been affected.

I would normally not write about a subject like this because I feel it is crass to talk about a family's tragedy.  However, there are certain other parties who don't seem to feel the same and are using this epidemic to score rhetorical points against the so-called anti-vax movement. Some of these people are suggesting that the deaths of the infants are because of the fear of vaccines while others are just suggesting that the current epidemic was worsened by this movement.

I think that using this outbreak to further your propaganda is quite simply wrong, especially when you don't even bother to get the facts correct.  So, to set the record straight, I wanted to point out a few simple things.

According to the CDC, pertussis outbreaks follow a cyclical pattern with larger peaks happening every three to five years. In general, the number of cases of pertussis have been on the rise since the 1980s  and outbreaks like this are not uncommon. The last peak was in 2005 when approximately 25,000 cases were reported in the US and 3,000 cases in California. As of June 2005, there were 1,261 cases in California which means the current outbreak is just sightly ahead of 2005.

The majority of the people who are getting pertussis this time are too young to have received the vaccine or to be fully vaccinated. Or to put this bluntly, the majority of the cases were not directly caused by parents refusing to vaccinate their children.  In children old enough to get the vaccine, the rate of vaccination in California is high, somewhere north of 95%.

That means that the problem is the people surrounding these very young children, these are the ones that are passing the illness to them. When there is a population that cannot get a vaccine for one reason or another, the goal is to vaccinate enough other people around them to prevent the illness from spreading - this is called herd immunity. This is an area where we will have to wait for data from CDC to be certain of what is going on, but I can make a few educated guesses.

First, the current vaccine does not provide long-lasting protection as the immunity gained from vaccines gradually fades over 6 to 10 years. This means that the majority of teenagers and adults do not have protection against pertussis making these populations the perfect staging ground.  And in fact, the majority of the cases over the past years have been centered in these groups and there is also some evidence that pertussis actively circulates in these populations in a milder form that might not be as readily noticed.

Second, according to the CDC, the current vaccine might not provide as effective as older vaccines were at providing immunity. To further complicate matters, the pertussis bacteria might be mutating into forms that are not covered by the existing vaccine.  There is a new version of the vaccine that was approved earlier this year that might help this situation.

Third, there are some hints that this outbreak is mostly impacting a population that, for social reasons, might not have as good vaccine coverage as would be expected.

When you put these facts together you are left with an illness that is increasing and has regular outbreaks and a vaccine that does not provide lasting immunity while at the same time loosing effectiveness in the cases that it does cover. I don't think it takes a genius to see what is happening here and it isn't that pesky "anti-vax" movement.

But, if you live in California and are around young children or other vulnerable populations and have not had a recent vaccination against whooping cough, now might be a good time to visit your doctor.


  1. You left out one of the most interesting pieces. This vaccine doesn't prevent carriage or transmission of pertussis. No herd immunity if vaccinated people can carry and transmit the illness.