Sep 30 2009

The HPV Vaccine

The Daily Mail reports of a 14 year old girl who died within hours of receiving the HPV vaccine (the brand being given in the UK is Cervarix, the better known brand is Gardasil). While this story is sensational and sure to stir up fears of the risks of the vaccine, a more sober look at the data shows that the vaccine has a very high safety record.

The bottom line is that we cannot interpret a single case such as this. As present there is no medical conclusion as to why the girl, Natalie, died. She stopped breathing, arrested, and could not be resuscitated. While tragic, this can unfortunately happen from a number of causes. It is plausible that the vaccine was a trigger, but it’s also plausible that it was not.

Of course, as a physician, a science writer, and a father of two young daughters I want to know what the data shows – what is the safety profile of the vaccine. (It’s somewhat misleading to ask “is it safe” although we often resort to this short hand, because it encourages a false dichotomy. Medical interventions are not all safe or all unsafe – they have a risk-benefit ratio. But it is reasonable to characterize the ends of this safety spectrum as either being basically safe or unsafe.)

Joe Albietz at SBM gives us the recent skinny of Gardasil safety, based upon recently published data. Here are the vital stats from the FDA:

“Every year, about 12,000 women are diagnosed with cervical cancer and almost 4,000 die from this disease in the United States.”

After distributing 23 million doses of Gardasil, there have been 772 serious adverse events reported, included 32 deaths. These are no greater than the background rate of reported events for a population this size.

In other words, safety monitoring of Gardasil has not revealed any pattern of excess deaths or serious outcome associated with the vaccine.

What this means is that all the data we have so far is compatible with the conclusion that Gardasil produces no serious side effects. It is possible that rare reactions are hiding in those numbers, but there has not been enough for a statistical pattern to emerge.

The benefit of the vaccine is that it is 94-100% effective in trials so far at preventing precancerous lesions from occurring (the very lesions that turn into cervical cancer). It is too early to say how many lives this will saved (it will be years before we see the effects of the vaccine on cervical cancer incidence), but it is likely that hundreds or even thousands of women per year will be spared death from cervical cancer by this vaccine.

Even if we assume that all 32 reported deaths were caused by the vaccine (very unlikely as that would mean otherwise there would have been zero deaths in the 23 million girls receiving the vaccine in the time period following the vaccine), that would still mean that the benefit of the vaccine outweighs the risk. And keep in mind the true number of excess deaths from the vaccine is certainly less than 32 and may be very close to zero.

Using a single case to promote fear is easy. Putting that case into statistical context is complex. But it is unfortunately true that people are more compelled by one vivid story than they are by mountains of data.


Update: The BBC has now reported that initial medical evaluation of Natalie indicates that she had a major underlying health condition that was likely the cause of her death and that the vaccine was unlikely to be a contributing factor to her death.

This makes sense, and is what I suspected. There are a number of known conditions, such as heart defects, that can lead to exactly what was described as happening to Natalie.

I will add any updates as they become available.

Thanks to “Truckle” for the heads up.

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