Thursday, March 26, 2009

A New Study on Gardasil / HPV Proves Perplexing

OK, this one has really left me scratching my head, and not a little worried. A new study published in the March 18 Journal of the National Cancer Institute (JNCI) set out to help predict “how HPV vaccination and HPV-based screening will influence cervical cancer prevention.”

Researchers took a look at both early (1213 cases diagnosed from 1985-1999) and invasive (808 cases from 1980-1999) cervical cancers in a New Mexico population.

They found that, yes, the majority—some 66.3 percent—of invasive cancers were indeed caused by the HPV strains 16 and 18 that are targeted by the HPV vaccines Gardasil and its British-born competition, Cervarix.

Type 16 caused 53.2% of invasive cervical cancers, type 18 caused 13.1%, and type 45 was responsible for 6.1%. On the early cancer front, Big Bad 16 lay behind 56.3% of cases, while HPV31 was responsible for 12.6% and HPV33 for 8.0%.

The researchers also found that the women who were diagnosed with invasive cancers caused by HPV16 were diagnosed on average at the age of 48; those with cancers caused by HPV 18 at almost 46; and those with cancers caused by other strains of HPV at the age of 52.3—several years later.

And here’s what’s making me scratch my head. Their discoveries caused the researchers to wonder whether, once sufficient herd immunity to HPVs 16 and 18 had been achieved via Gardasil, women could begin cervical cancer screenings a few years later. After all, if the strains left active generally take longer to cause trouble, wouldn't that make sense?

It’s important to figure this out because the cost-effectiveness of Gardasil is pretty dubious. The three-shot series is expensive, running at $360 plus the cost of administration; health insurance will usually cover a part of the cost. Cash-strapped families aren’t left out—Gardasil is freely available to impecunious girls up to the age of 18 at an estimated cost of $1 billion in taxpayer dollars.

According to the New England Journal of Medicine all those shots for 12-year olds would work out at $43,600 per quality-adjusted life-year (QALY) gained, although a temporary catch-up program for girls up to age 18 would cost $97,300 per QALY, and extending the vaccination program to age 26 would cost $152,700 per QALY

The math just about works for the younger crowd—unless equally expensive booster shots or reformulated shots prove to be necessary, something that Merck flat-out knows nothing about but that many experts consider likely.

So if you could skip a few years of exams, that would make it all sound so much more efficient. (Assuming that you’re happy for your health to be boiled down to a matter of dollars and cents--although, to be fair, early screening is said by some to lead to unnecessary and frightening interventions.)

Just a couple of problems.

When the English branch of Britain’s National Health Service switched the age of young women’s first Pap smear screening from 20 to 25, they found that far fewer women came in for screenings, presumably because they’d never got into the habit. Changing the screening age (currently recommended at age 21 or three years after beginning sexual activity in the US) is a dangerous path to stray down for so many reasons—just for a start, you'd have to assume that patterns of HPV infection wouldn't change. Which leads me to the next issue.

The JNCI study also found that the number of both early and invasive HPV16-caused cancers has been decreasing over the last few years, while the number of cancers caused by HPV strains other than 16 and 18 has been proportionately increasing—an extremely worrisome trend if you are relying on inherently-limited Gardasil, which only targets 16 and 18 for preventing cancer, to take care of you. Even now, this study found that 16 and 18 caused only 66.3% of cervical cancers, while the number had previously been reported at around 70%.

Add to that the threat of replacement disease, whereby other strains happily rush to fill the void left by targeted strains, and our daughters could be left pretty vulnerable.

Probably not the best time to think about delaying screeings.

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