Does @VaxCalc Provide Valid Info on Vaccines? Not Really...

Twitter can be a really useful tool for getting information out to lots of people in a very short amount of time. The down side is that the 140-character limit on your message means there isn't a whole lot of space for nuance or detail. This leaves plenty of room for misinterpretation of messages. It also means that those with an agenda to drive can ignore nuance in favor of their own spin. For example, the Twitter account @VaxCalc, run by the Orwellian named National Vaccine Information Center (NVIC). @VaxCalc pumps out a steady stream of...uh...words (I refuse to call it "information," since it is nothing of the sort) that, while containing a speck of a grain of truth, aim to persuade people away from vaccines. Don't believe me? Have a look:

But I thought they removed it!

The link in the tweet takes you to a table on the FDA's web site about thimerosal in vaccines. Thimerosal, as most of you know, is a preservative that is used to prevent vaccines from being contaminated with bacteria, fungi or viruses, which can be very bad, indeed (as evidenced by the 1928 Bundaberg Disaster, in which 12 children died because a vaccine became contaminated). It caused a stir because it is metabolized into ethylmercury, which some erroneously linked to autism.

Anyway, is that tweet correct? Well, yes and no.

The table that @VaxCalc direct followers of @VaxCalc to lists 44 vaccines, of which 15 are listed as having at least a trace of thimerosal, as of March 2008. That works out to 34% of the vaccines listed. Here's where the spin starts.

@VaxCalc purports to give parents good information regarding vaccines, so they can make supposedly informed decisions regarding their children. By pointing out that as of 2008, 34% of U.S. vaccines contained thimerosal, they appear to be implying that thimerosal wasn't actually removed from vaccines back in 2001. Around 2000-2001, FDA recommended that thimerosal be removed from vaccines that are administered routinely to children as a precaution, since at the time, concerns were raise about mercury, but there was insufficient evidence to say with certainty whether its use in vaccine preservatives was safe or not. Since then, numerous studies have shown that there are no observable adverse effects from using thimerosal to keep vaccines free of contaminants. At any rate, at the time, it was a reasonable precaution, and so vaccine manufacturers stopped using it for pediatric vaccines. The last thimerosal-containing lots would have expired around the end of 2001 or beginning of 2002. Misinformation #1.

In the tweet, no distinction is made between vaccines containing larger amounts of thimerosal and those containing only trace amounts. Of the 15 vaccines listed that have some thimerosal in them, 7 (or only 16% of those listed) have only a trace (i.e., less than 1 µg per dose). Trace amounts exist because some component used in the production of the vaccine contained thimerosal. Once the vaccine has been made, it is processed to remove the thimerosal, which gets almost all of it out, though because nothing in life is ever perfect, tiny amounts remain. The resulting vaccine has so little thimerosal in it that it would not cause problems, even if there were significant adverse effects from the amounts found in some pre-2001 vaccines (which, as I've already pointed out, was not the case). In other words, they're trying to pad their numbers in an effort to make things seem scarier than they are. Misinformation #2.

Their count includes vaccines that are not routinely given to children, such as the vaccine for Japanese encephalitis or tetanus toxoid. This, again, pads their numbers so that it appears that there are more vaccines that parents should worry about than there actually are. Had they actually looked only at those vaccines given to children, their number would not have been nearly as impressive. Misinformation #3.

@VaxCalc's choice of phrasing is also somewhat misleading. They mention their sample includes "all US licensed vaccines" as of 2008. On a casual reading of that, one might think that all of the vaccines were actually in active use, being manufactured, sold, administered to people, etc. However, that is not the case. The table lists vaccines that, as of 2008, had received approval from the FDA and were licensed for distribution in the U.S. That does not mean, however, that the makers of the listed vaccines were actively marketing them. When I wrote to CDC for clarification of the table, my assessment was confirmed:

While these vaccines are licensed for distribution in the U.S., not all of them are sold in the U.S. That is a business decision made by the license holder, not FDA.

For example, if you take a closer look at the table, you will see that it includes smallpox vaccine. Yet smallpox was eradicated worldwide decades ago, and its vaccine is no longer routinely administered. So it isn't exactly representative of what people were actually receiving nor of how much thimerosal to which they were really exposed. Misinformation #4.

It's also an old and incomplete list. While finding the information is a bit more difficult (you have to actually look in the package inserts), the complete list of licensed vaccines is a bit more extensive, listing 72 vaccines that have current, active licenses. Because I love my readers so much, I actually went through the work of looking at each vaccine in that list for which additional information was available. Here are the results (with even more info, like route of administration). Note, doses are the pediatric doses unless otherwise noted.

Click to enlarge

As we can see from that list, there are 13 vaccines out of 72 that have at least a trace of thimerosal, or only 18% of approved vaccines. If we only look at those with more than a trace, we have 6 out of 72, or 8%. That's quite a bit less than the 34% claimed by the @VaxCalc. A number of these, like the more abbreviated list linked to by @VaxCalc, are not in current routine use, even though the manufacturers would be allowed to produce and distribute them at any time. Misinformation #5.

Now, you might have noticed something about the numbers here. The other list had 15 vaccines that contained thimerosal. Why are there only 13 here? Well, some of those vaccines come in two different formats: single-use syringes and multi-dose vials. @VaxCalc did not differentiate. Instead, they picked only the format that contained thimerosal. If I include those, my percentages change to 20% and 11% respectively. This isn't immediately obvious just looking at the table to which @VaxCalc linked. I didn't even notice it until I actually went through the full list of approved vaccines. But the information is there, so once again, we see that they are being misleading by picking only those vaccine formulations that fit their agenda. Misinformation #6.

It should be painfully obvious by this point that the short little tweet from @VaxCalc via its @VaxCalc twitter account is less than honest. To put the information in its proper context took significantly more space than could be done in 140 characters. All of this is what was missing, the nuance and finer details necessary for an individual to form a truly informed opinion, rather than the misinformed one that @VaxCalc would prefer.

And this is but one example. Their tweet stream is filled with hourly tidbits of fear, uncertainty and doubt, all designed to mislead and misinform the casual reader.