Tuesday, October 29, 2013

Black Women May Be Less Likely To Be Protected by the HVP Vaccine

Think Progress writes about this:

The human papillomavirus (HPV) vaccine that has cut teen girls’ risk of cancer in half is less likely to shield African American women, according to new research unveiled Monday. Black women, who have higher rates of cervical cancer than the general population, are susceptible to different strains of HPV than the most common types for white women. Unfortunately, the only approved HPV vaccines in the US target the strains that most affect white women, leaving black women more or less unprotected.

The likely reason?  The strains of HPV which are most common in white women are not necessarily the most common in black women, and the vaccine protects against the most common strains found in clinical trials before its creation.  Because there are more white women, the results are driven by the fact that they were the majority in the clinical trials for the vaccine, because they are still the majority racial group among US women.

But those clinical trials may have also included too few black women.*

In developing Gardasil and Cervarix, scientists relied on studies to pinpoint the strains of HPV most likely to lead to cancer. Studies were done on all ethnicities, Hoyo said, noting that there may have been insufficient numbers of black women in the research studies to pick up the differences in HPV subtypes.
"There has always been some skepticism about whether there are other strains that are important, other than 16 and 18," she said. This study is not the first to report the differences, she said.

And Think Progress:

The HPV vaccine is hardly the only medical breakthrough that failed to account for racial differences. Even though the Food and Drug Administration has mandated proportional representation of minorities in clinical research, minorities are still drastically undercounted. One recent report found that many clinical trials exclude non-white subjects; the Hepatitis C vaccine trial, for instance, was 83 percent white, 14 percent African American, 2 percent Asian, and 2 percent other. Latinos, who comprise 16 percent of the total U.S. population, account for just 1 percent of clinical trial participants.

The problem may be more complicated when there are major (and perhaps previously unknown) differences in the incidence or form of a disease in different racial groups (such as the case of different strains of HPV being most common here).   A group small in numbers (say, American Indians) might not be under-counted in a study, compared to their population size, but because of the nature of those differences it should really be analyzed separately.  This requires taking larger samples of small population groups, because small samples have more scope for the effects of sampling error.

Many epidemiological studies already do that, in any case.  But these news are a good reminder that there are real reasons for  including women and men of all racial groups in clinical trial studies when the diseases apply to all of them.

Should black women get the currently available vaccine?  The general answer seems to be that they should.  It still gives protection against two strains.  But its protective value may be lower for them than for white women, and the vaccine should either be adjusted or offered in different forms for different racial groups.
* I can't figure out from just the summaries if this means that black women were not their population percentage in the trials but fewer, or if they were represented in their population percentage, but the numbers were too small to bring out the strain differences.