Two doses, possibly even 1 dose, of the HPV16/18 vaccine may provide protection equal to the standard 3-dose schedule against persistent HPV16/18 infections, according to an analysis of data taken from women who missed 1 or more prescribed doses in a vaccine trial (Kreimer AR, et al. J Natl Cancer Inst. September 9, 2011. Epub ahead of print).
At 4 years postvaccination, vaccine efficacy (prevention of incident HPV16 and HPV18 infections that persist for at least 1 year) was found to be 80.9% for 3 doses, 84.1% for 2 doses, and 100% for 1 dose.
The investigators cautioned against generalizing their results because of how the study was conducted. Their study involved the bivalent HPV16/18 vaccine, and their results may not apply to other vaccine formulations. In addition, this study was conducted with women in Costa Rica, and other populations may have more comorbidities, such as endemic parasitic infections