Fewer than 3 doses of HPV vaccine effective, new study finds

September 15, 2011

The current protocol for HPV 16/18 vaccine, 3 doses over 6 months, can be expensive and inconvenient. Now, a new study suggests that fewer than 3 doses may be just as effective as the standard 3-dose regimen when it comes to preventing cervical cancer with one of the approved vaccines. Find out how this discovery came about and how it potentially could be used to increase vaccination rates.

A new study on the human papillomavirus (HPV) vaccine and an accompanying editorial raise an intriguing question: Is this a situation where less is more?

Study results suggest that fewer than 3 doses may be just as effective as the standard 3-dose regimen when it comes to preventing cervical cancer. The HPV 16/18 vaccine currently is administered in 3 doses over 6 months, which can be expensive and inconvenient, leading researchers to try to determine how many doses really are necessary.

Researchers from the Division of Cancer Epidemiology and Genetics, National Cancer Institute (NCI), National Institutes of Health, analyzed data from the NCI-sponsored Costa Rica Vaccine Trial, which tracked women who received either 3 doses of Cervarix or the control vaccine.

Because of factors such as pregnancy or gynecologic procedures, 20% of the 7,466 women enrolled in the study actually received fewer than 3 doses. That allowed researchers to compare the frequency of persistent HPV infection in the different groups-those who received 3 doses (5,967 women) versus those who received 1 dose (384) or 2 doses (802) in a 4-year follow-up.

Protection levels were found to be similar for all groups, and the effectiveness of fewer doses could be especially important when the cost and/or logistics of administering the vaccine are a problem.

“Our study provides evidence that an HPV vaccine program using 2 doses will work. It may be that vaccinating more women, with fewer doses for each, will reduce cervical cancer incidence more than a standard 3-dose program that vaccinates fewer women,” said lead study researcher Aimée R. Kreimer, PhD. “The main question will be whether the duration of protection from fewer doses is adequate.”

The results were surprising because other subunit vaccines typically require at least 2 shots, but the researchers also cautioned that more studies need to be done for longer periods than 4 years to determine whether fewer than 3 doses can provide continuing strong protection.

Cervarix is 1 of 2 vaccines approved by the US Food and Drug Administration (FDA) to protect against the 16 and 18 types HPV that are responsible for 70% of cervical cancer cases. Because the formulations are different, it is not known whether the same results would be obtained with the other FDA-approved HPV vaccine, Gardasil. The Centers for Disease Control and Prevention recommends that girls beginning at ages 11 to 12 be vaccinated against HPV.

Cosette Marie Wheeler, PhD, of the Department of Pathology and Department of Obstetrics and Gynecology at the University of New Mexico Health Sciences Center, called for more studies to evaluate the efficacy of 1, 2, and 3 doses of the vaccine for adolescent girls. "The age old adage of less is more may apply to HPV vaccination and if so, the report . . . represents an important step on the road to more effective and sustainable cervical cancer prevention programs.”

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