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Home HPV Vaccines HPV Vaccines Two Doses of Cervarix® Work as Well as Three?

Two Doses of Cervarix® Work as Well as Three?

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Findings from National Institutes of Health research in Costa Rica suggests that two doses of GlaxoSmithKline’s cervical cancer vaccine Cervarix® works virtually the same as the full three dose regimen in blocking HPV infections (and even a single dose may have some benefit, too).

Cervarix® is a bivalent vaccine that works against HPV 16 and HPV 18, respectively, the two “high risk” types of the virus found in approximately 70% of cervical cancers worldwide. The Costa Rica Vaccine Trial is a study to assess how well Cervarix® works in preventing persistent HPV16/18 infections and related precancers, while also assessing the vaccine’s efficacy in preventing infection with three HPV types (31,33,45, respectively) not covered by the vaccine but for which cross-protection has been demonstrated in previous research.

Women in this study were randomized to receive three doses of either Cervarix® or GSK's hepatitis A vaccine, Havrix®. While all subjects were slated to receive a full three dose regimen with either vaccine, 20% of the women received fewer than three doses (most often due to pregnancy or referral to colposcopy due to cervical diseases being detected). This gave the authors a chance to look at how well the vaccine worked in those who received only one or two doses.

With median follow up of 4.2 years, efficacy against 12-month persistent HPV 16/18 infections in women who were given all three doses (n=2,957) was 80.9%. Among those who received two doses (n=422), efficacy was 84.1% and, somewhat surprisingly, no persistent infections were found in 196 subjects who only had a single dose. (The fact that efficacy increased as the number of doses fell was not significant.)

The authors say more research will be needed to fully understand the impact of women receiving fewer than three doses. The relatively small number of women who received one-or two-doses prompts caution among some observers, for example, and the researchers note that other populations (such as those with impaired immunity) might not have same results. Also, they point out that this study suggests a full three dose regimen confers greater cross-protection against related HPV types not covered by the vaccine, and it isn't known how long the duration provided by fewer than three doses may last. Still, this is encouraging and the authors say their findings present provides the " the first clinical evidence that two doses of the bivalent HPV vaccine are highly efficacious in the prevention of incident HPV16 and HPV18 infections that persist for at least 1 year, and that even a single dose may be highly efficacious."

The implications of these findings are important: while HPV vaccines work well, a hurdle is the cost and inconvenience associated with giving multiple doses over half a year. Both Cervarix® and Merck’s HPV vaccine, Gardasil®, are given in three doses over six months. This is especially challenging in the developing world (where 80% of cervical cancers occur), as even a single clinic visit is a challenge for many patients.

Reference
Aimée R. Kreimer, Ana Cecilia Rodriguez, Allan Hildesheim, Rolando Herrero, Carolina Porras, Mark Schiffman, Paula González, Diane Solomon, Silvia Jiménez, John T. Schiller, Douglas R. Lowy, Wim Quint, Mark E. Sherman, John Schussler, Sholom Wacholder; for the CVT Vaccine Group. Proof-of-Principle Evaluation of the Efficacy of Fewer Than Three Doses of a Bivalent HPV16/18 Vaccine. Journal of the National Cancer Institute, 2011. 103:1-8.