10 (sporadic) years of JournalClub
I started JournalClub 10 years ago, posting a summary of an article about HIV on November 27, 1995. It’s been sporadically active since then, though recently dormant.
November 8, 2005
Check out this Journal Club
My attention was drawn to this recently launched website, that aims to act as an online journal club. It is just getting rolling and has some bugs, but is quite interesting. Rather than try to describe it, I suggest checking it out:
September 19, 2005
Site currently snoozing
Journalclub has been asleep since June. Since the vast majority of comments currently being submitted are spam, I am deactivating the comment facility for now.
Should Journalclub awake from its slumber, I will reactivate comments.
June 3, 2005
The zoster vaccine
The lead article in yesterday’s NEJM, A vaccine to prevent herpes zoster and postherpetic neuralgia in older adults, presents the results of a VA Cooperative Study looking at the efficacy of a high potency, live attenuated VZV vaccine developed by Merck from the Oka/Merck strain. The results are encouraging, with a reduction in the incidence of herpes zoster of 51.3% during 3 years of follow-up.
The authors state that the incidence of post-herpetic neuralgia was reduced by 66.5%. They are referring to the incidence in the overall study population: there were 27 cases of PHN among the 19,254 subjects who received the vaccine, vs. 80 cases among the 19,247 subjects who did not receive the vaccine. If you look at the number of cases of PHN among patients with zoster, the numbers are 27/315, vs. 80/642, a reduction of about 31%. Both of these numbers are important to judge the vaccine.
In other words, the vaccine reduced the incidence of zoster by about a half, the overall incidence of PHN by about 2/3 and the incidence of PHN among patients with zoster by about a third.
What about the choice of vaccine? The study used a live attenuated vaccine that was of higher potency than the standard vaccine given to children. Why not study the vaccine that is already available in the United States? Two reasons, one medical, one economic:
- Medical: a higher potency vaccine may be necessary to boost the immune response in older patients sufficiently to prevent zoster.
- Economic: a new vaccine formulation for this specific purpose can be priced much higher than the already available childhood vaccine.
Turning to the economic consideration first, in the accompanying editorial, Gilden states:
“To nonindigent recipients of the currently used childhood VZV vaccine (Varivax), the price of vaccination is between $50 and $100 (the sum of the cost of vaccine plus the visit or facility fee). An adult vaccine might cost more, given its greater potency. Nevertheless, the zoster vaccine appears to have been highly cost-effective in the Shingles Prevention Study (i.e., in the range of $2,000 per quality-adjusted life-year gained, even assuming a vaccine cost of $500).”
Clearly, Merck stands to make a lot of money if the vaccine used is a new one, costing several hundred dollars, rather than the existing vaccine which costs under $100 per dose.
What about the possibility of using the currently available vaccine, possibly with a booster dose, rather than a new, higher potency one? The vaccine used in this study contained between 18,700 and 60,000 plaque-forming units of virus, versus about 1,350 pfu’s in the Oka/Merck vaccine that is commercially available and is administered to children. In the concluding paragraph of the current study, the authors state:
“The minimum potency of the zoster vaccine administered to subjects in the study was at least 14 times greater than the minimum potency of Varivax (Merck), the vaccine currently licensed to prevent varicella. A preliminary study indicated that potencies of this magnitude are required to elicit a significant increase in the cell-mediated immunity to VZV among older adults — hence, the need to formulate a high-potency vaccine for this study. We know of no data to suggest that the licensed varicella vaccine would be efficacious in protecting older adults from herpes zoster or postherpetic neuralgia. Thus, we do not recommend the use of the current varicella vaccine in an attempt to protect against herpes zoster and postherpetic neuralgia. “
The authors provide no references to back up the results of their “preliminary study” indicating that such high potencies are necessary. In fact, a 1992 article published by some of the same authors of the current study, Immune response of elderly individuals to a live attenuated varicella vaccine, seems to indicate that such high doses may not be necessary. From the abstract of that article:
“The Oka strain live attenuated varicella-zoster virus (VZV) vaccine was administered subcutaneously to 202 VZV-immune individuals who were 55 to greater than 87 years old. The dose administered varied from 1100 to 12,000 pfu… Most significantly, VZV-specific proliferating T cells in PBMC of vaccinees were increased in frequency from 1 in 68,000 to 1 in 40,000… Dose and age of the vaccinees did not significantly influence the magnitude of the mean cell-mediated immune response…”
I understand that pharmaceutical companies may reformulate a drug before launching a large, expensive trial for a new indication, in order to maximize their profit. That’s how the health care market works. And it may well be that a higher potency vaccine is necessary to achieve adequate protection.
Still, it would have been nice if the authors of this trial had justified their use of a new vaccine with a published reference.
May 30, 2005
Why don’t we just put statins in the water supply and be done with it?
Statins and the risk of colorectal cancer in last week’s NEJM is a case-control study from Israel that looked at about 2000 patients with colorectal cancer and a similar number of controls, and found that “the use of statins for at least five years (vs. the nonuse of statins) was associated with a significantly reduced relative risk of colorectal cancer”. The odds ratio was about 0.50.
At the risk of sounding like a broken record, this is yet another case-control study, useful as hypothesis generating, but not much else. The authors performed their analysis adjusting for multiple co-variates, such as aspirin use, vegetable consumption, red-meat consumption, but there is no way they can sufficiently adjust for all variables to convince me.
For one thing, they don’t mention adjusting for low-saturated fat diets which patients who take statins are likely to adhere to. And there are sure to be other confounders associated with statin treatment.
The one fact that almost convinced me was that the authors found no protective effect from non-statin cholesterol lowering agents (fibrates). These are likely to be associated with most of the same confounders as statins. BUT, there were only 20 patients taking these drugs, too few to be statistically reassuring, and the reason for prescribing a fibrate rather than a statin is more likely to be hypertriglyceridemia than hypercholesterolemia, implying a different population and perhaps a different diet as well.
Medpundit is also critical of this study. I have to disagree with her main argument against it, however. She feels that the biggest flaw is that the two groups were not matched for ethnicity, with a higher percentage of Ashkenazi Jews in the cancer group. However, in their adjusted analysis, the authors specifically state that they adjusted for ethnicity. In my opinion, the biggest problem with case-control studies is not that they do not adequately adjust for known confounders, but rather that they don’t take into account confounders they have not thought of.
Powered by WordPress
Visitors since November 1, 2004:
