The study found that 111 of the 1,004 unvaccinated women were diagnosed with infections of HPV types 6, 11, 16 or 18 between 2009 and 2016.Yet only four of the 106 women vaccinated with one dose; seven of the 126 women vaccinated with two doses; and 14 of the 384 women vaccinated with three doses were diagnosed with those infections during that time period."Our study suggests that US women who received 1 dose of the HPV vaccine may have gained similar protection against vaccine-type infections compared with those who received additional doses," the researchers wrote in the study. "These findings support previous observational studies and post hoc analyses of vaccine trials that demonstrated comparable effectiveness of 1 dose to 2 or 3 doses.