What's With Mosquito Repellent Patches?

I just saw an ad in my current Canadian Gardening magazine for a patch which claims to repel mosquitoes. Having an intense hatred for all biting insects, I was intrigued, though suspicious of its efficacy. The "OmeZone Insect Defend Patch" apparently contains thiamine (vitamin B1), which is released into your system through your skin. It starts acting within 2 hours and can deter mosquitoes for up to 36 hours, according to the ad. It is promoted as safe for children and pregnant women, which probably appeals to the people who are cautious about synthetic chemical repellents. It costs $6.95 for a pack of 5. My questions about the patch:
(1) How does it work? I have read that it essentially makes you appear stinky to mosquitoes. A repellent odor oozes out in your sweat, though this is not apparent to other humans.

(2) Does it work for all kinds of mosquitoes, including Culex tarsalis (spreads West Nile virus in this province), and the Aedes and Anopheles species? I can't find any published articles demonstrating its proposed effect. If it is effective, then why hasn't this been already used widely in prevention of malaria.

(3) Why not just take oral thiamine, if this purpose is to get it into your body and into your sweat?
Stewart C. Harvey, Ph.D. recommended 100 mg of vitamin B₁ as an effective mosquito repellent in a 2002 comment to the New England Journal of Medicine (not a study or review article). The oral thiamine is certainly cheaper. One major drugstore sells thirty 100 mg tablets for $5.41. I suspect the patch format fools the general public into ignoring the fact that this is still a drug acting on your body, albeit an essential vitamin. Perhaps the manufacturer aims to make the drug more long-acting by formulating it as a transdermal patch? In that case, I'd probably rather just take a few tablets of the thiamine over the course of 36 hours.

Other reasons to use a patch:
(a) you can't take anything orally because you are unconscious or don't have a functioning gastrointestinal tract
(b) you want to avoid metabolism of the drug in the liver (which does not apply to thiamine, but commonly applies to hormones) or
(c) you want a slow steady release of the drug over time (good for narcotics, nicotine, and hormones).

(4) Are there any good studies on humans that show that a thiamine patch is effective in repelling mosquitoes?
A search of OVID Medline with the search terms "mosquito" and "thiamine", limited to English and humans, revealed only 4 articles. Only one had an abstract (Journal of the American Mosquito Control Association. 21(2):213-7, 2005 Jun.). It described their study, where oral B vitamin complex supplements failed to have a relationship to the mosquito repellent qualities of the compounds released from the participants' skin. There were no articles on the transdermal (patch) use of thiamine.

A July, 2002 article in the New England Journal of Medicine has a very pertinent study of the efficacy and duration of action of several different repellents (thiamine not included), noting that 10% citronella oil can protect you for all of 19 minutes!

(5) Would I rely on this product to protect me in a country where malaria is endemic? Absolutely NOT!

Note these sad facts: More than 40% of the world's population is at risk of malaria, and more than a million people die of it each year. Malaria kills a child every 30 seconds: 90% of people who die from malaria are children not yet 5 years of age, and most (90%) of these deaths take place in sub-Saharan Africa. (Greenwood BM, Bojang K, Whitty C, et al. Malaria. Lancet 2005;365:1487-8.)

One website promotes this product by asking: "Are you planning to travel abroad to areas possibly infested by various insect populations?" and "Are you in an area where you know that mosquito-borne diseases are present?" Unless they mean northern Canada or parts of the USA, where the mosquitoes don't carry malaria, this is a reckless product recommendation. If I had to decide what product to use to prevent my own DEATH, I'd probably go with the one that has substantial evidence to prove that it works (DEET + prophylactic antimalarial oral medication + permethrin-treated bednets).

Aside from malaria, I know for sure that there are no published studies showing that this patch has any efficacy for prevention of yellow fever, dengue fever, Japanese encephalitis, or any of ther other mosquito-borne diseases.

(6) Should pregnant women use products like this because they are safer than the alternatives?
It should be pointed out that pregnant women need particularly good protection from malaria (DEET and certain antimalarials are okay), since malaria will kill a fetus and occasionally the mother too, since immunity is lower in pregnancy. Several deaths have occured in Canada due to misinformation on the prevention or treatment of malaria in travelers. If we are just talking about nuisance mosquitoes, then you may as well use any product that isn't known to be unsafe.

The Canadian Medical Association Journal published a critical review (DEET-based insect repellents: safety implications for children and pregnant and lactating women. August 5, 2003; 169 (3)) which concludes that "There is no evidence that the use of DEET by pregnant or lactating women poses a health hazard to unborn babies or children who are breast-feeding."
Another quote from the promotional website: "Just one small OMEZONE TM Defend Patch, applied discreetly on any hairless area of the body creates an invisible virtually impenetrable shield against the ill effects of mosquitoes and the diseases they may carry."

Yeah, well I'll bet that the mosquitoes probably find it hard to bite you THROUGH the patch. I propose that the application of several hundred patches, so as to cover every bit of exposed skin, would be effective as a mosquito repellent.