December 2009: HPV vs. Flu adverse event rates

This month wraps up 2009, a year that had more VAERS reports than ever before. In past months I have focused on the growth of VAERS reports related to both Seasonal and H1N1 Flu as well as HPV vaccinations. This month, I will do something different and explore a question of vaccine safety. Which vaccine has a higher chance of causing a VAERS injury report to be filed: H1N1 Flu or Human Papiloma Virus (HPV)?

The chance of having a VAERS injury report filed is equal to the number of VAERS reports, divided by the number of people vaccinated. We can ask MedAlert or CDC Wonder for the number of VAERS reports, but we don't know how many people were actually vaccinated. However, many estimates have been made, and we can find these numbers on the Internet.

First let's look at H1N1 Flu. What percentage of people given an H1N1 Flu vaccination file a VAERS injury report?

The Washington Post claims that 20% of Americans got the H1N1 Flu vaccine (as of January 16, 2010). They claim that this is 61 million people.

How many VAERS reports were generated by these 61 million vaccinations? As of January 29, there are 9319 reports of injuries associated with H1N1 Flu. And given the rate of growth of these reports, this number can easily grow to 12,000 in the next two months (see graph). Given that it takes a few months for people to get their injury reports into the VAERS system, it is not unreasonable to consider 12,000 as a conservative estimate.

The red dot in the upper-right is a projection based on the slope of the curve. It predicts that there will be 12,000 VAERS reports associated with H1N1 Flu by the end of March. The latest real data point (the rightmost blue dot) is on January 29 and lists 9319 reports.

If 61 million people were vaccinated, and 12,000 of them filed injury reports, that's one injury report for every 5000 vaccinations. If we discard the projection of 12,000 VAERS reports and stick to the current numbers, we get a conservative estimate of one injury report for every 6500 vaccinations.

Next let's look at HPV. What percentage of people vaccinated against HPV file a VAERS injury report?

According to the FDA over 23 million doses of Gardasil were distributed in the three-year period of 2006-2008. Assuming a constant rate of distribution, this means about 30 million doses up to the end of 2009. Considering that it takes three doses of Gardasil to immunize someone, it really means that 10 million people have been vaccinated with Gardasil. And if you think that these numbers are wrong because there are other HPV vaccines besides Gardasil, consider that nearly 99% of the HPV-related VAERS reports specifically mention Gardasil, so it is safe to say that 10 million people have been vaccinated for HPV.

How many injury reports have been filed for HPV? As of January 29, there are 17,822 VAERS reports associated with HPV. So if 10 million people were vaccinated, then 1 out of every 560 people vaccinated filed a report.

Assumptions

There are many assumptions and likely inaccuracies in these calculations. Let me list a few of them:

• I assumed that the number of doses of Gardasil distributed in 2009 grew at the same rate as it did in 2006-2008, but it surely did not. In fact, it probably increased. This means that more people were vaccinated than 10 million, and my estimate of the chance of filing a report is too high.
• The FDA reported the number of Gardasil doses distributed, which is, of course, more than number of doses actually administered. This means that fewer than 10 million people were vaccinated, and my estimate of the chance of filing a report is too low.
• Not every patient gets all three doses of Gardasil. This means that more people were vaccinated than 10 million, and my estimate of the chance of filing a report is too high.
• The HPV calculation does not account for future VAERS reports based on vaccinations already given, and the H1N1 Flu calculation makes a conservative guess that all reports will be filed in two months. This means that there will probably be even more VAERS reports, and my estimate of the chance of filing a report is too low.

The point I'm trying to make is that numbers are easily manipulated. Everyone does it, and so do I in these calculations. But I want to show that I'm trying to be fair.

Conclusion

1 out of every 560 people who are vaccinated against HPV files a VAERS report. 1 out of every 5000 to 6500 people who are vaccinated against H1N1 Flu files a VAERS report.

So if you get the HPV vaccine, you are about 10 times more likely to end up filing a VAERS report than if you had gotten the H1N1 Flu vaccination.

Tip of the Month for using MedAlerts or CDC Wonder

Many of you will want to verify these numbers for yourselves. When you do, keep in mind that a vaccine may have multiple codes. For example, the code "HPV4" is for Gardasil, "HPV2" is for Cervarix, and "HPV" is used when the manufacturer is unknown. As far as H1N1 Flu codes go, there is "FLU (H1N1)" for the injection, "FLUN (H1N1)" for the nasal dose, and "FLUX (H1N1)" for unknown manufacturers. The proper way to count the number of VAERS reports associated with a vaccination is to select all of the relevant codes in the search form.

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