Although Black women are twice as likely as White women to die from cervical cancer, Human Papillomavirus (HPV) vaccination may not prevent cervical cancer in African-American women, according to a new study.

The available vaccines only protect against four strains of HPV, which, according to this study from the Duke University School of Medicine, African-American women are half as likely as White women to carry.

The American Cancer Society expects more than 12,000 women to be diagnosed with cervical cancer this year alone. Incidence rates have been falling for all women as screenings have become more routine, but the rate of infection for Black women is the second highest (after Latinas) – and it’s still 39 percent higher than their White counterparts.

Black women have been significantly more likely than any other group to die from cervical cancer.

The study examined 280 Black women and 292 White women, all carrying varying HPV strains – some had no signs of cancer, some showed mild signs of pre-cancer, and a small percentage had advanced precancerous abnormalities. In the group with the most advanced signs of pre-cancer, White participants carried strains 16, 18, 33, 39 and 59, whereas Black participants carried strains 31, 35, 45, 56, 58, 66 and 68.

Currently, two vaccines on the market target four HPV strains considered most troublesome. Gardasil, which is produced by Merck and can be administered to anyone age 9 through 26, protects against strains 16, 18, 6 and 11. Cervarix, by GlaxoSmithKline, is available only for girls and women and targets strains 16 and 18. (The vaccines also protect against less-common genital cancers in both men and women).

“Compared with white women, we saw that African-American women had about half as many infections with HPV 16 and 18, the subtypes that are covered by HPV vaccines,” said study co-author, Adriana Vidal. “Since African-American women don’t seem to be getting the same subtypes of HPV with the same frequency, the vaccines aren’t helping all women equally.”

The vaccines are based on these strains because strains 16 and 18 are found in 70 percent of cervical cancer cases, while strains 6 and 11 are associated with 90 percent of genital warts cases, according to the National Cancer Institute. However, studies have a long-documented history of overlooking the need for diverse participants in pharmaceutical and medical trials.

HPV is a common virus that is easily spread by skin-to-skin contact. It is possible to have HPV without knowing it, so it is possible to unknowingly spread HPV to another person, according to the CDC.

There are more than 100 strains of the human papillomavirus and they can affect several parts of the body. Most strains are minor threats to a healthy immune system, which can naturally terminate an infection over time. Though the virus can cause warts, most people who become infected exhibit no symptoms.

More than 40 strains of HPV are specifically passed through sex. It’s the most common sexually transmitted disease in the United States, and the Center for Disease Control says that most sexually active people will contract at least one type in their lifetime.

Duke University’s study is limited by its sample size. But if it reflects a larger trend: African American women are much less likely as White women to carry these forms of the virus and are thus less protected from the cancers they cause.

Many researchers have been closely following the data to see if the vaccines are actually affecting HPV infection rates.

A study published this past June 2013 in The Journal of Infectious Diseases has compared HPV rates among girls age 14 through 19 from before Gardasil hit shelves (2003-2006), and after (2007-2010). Between the time periods, infection rates were cut in half for strains 16 and 18, nearly eliminated for strains 6 and 11, and trimmed for milder, less common strains. The results are being touted as proof that the vaccines are indeed curbing HPV among teens, and by extension, will curb cervical cancer in the future.

But for whom?

In the case of high-risk strains that aren’t covered by the vaccine – such as 35, 66, and 68, the strains most prevalent in Black women – the report states the decline was too miniscule to be statistically relevant. These strains aren’t even pictured on the study’s dramatic-looking bar graph. To be fair, though, the low-risk strains prevalent in Black women also saw major declines.

This study’s population was reflective of American demographics. Additionally, sexually active, unvaccinated girls were included – 20 percent were African American, 56 percent White, and 23 percent “Other.”

Neither Merck nor GlaxoSmithKline has addressed the lack of coverage for HPV strains prevalent in African American women, though neither company has ever addressed public and legislative controversy surrounding the HPV vaccine.

Merck is currently testing an updated HPV vaccine that fights nine dangerous strains instead of four (6, 11, 16, 18, 31, 33, 45, 52 and 58). Although their preliminary study results are promising, the disparity will likely remain.

“The most disconcerting part of this new vaccine is it doesn’t include HPV 35, 66 and 68, three of the strains of HPV of which African-American women are getting the most,” said study co-author, Cathrine Hoyo. “We may want to rethink how we develop these vaccines, given that African-Americans tend to be underrepresented in clinical trials.”

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