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Australian Cohort Study: 1 Dose of HPV Vaccine as Effective as 2 or 3 Doses

JUL 31, 2019 | ALEXANDRA WARD
One dose of prophylactic human papillomavirus (HPV) vaccine protected as well as 2 or 3 doses against high-grade cervical pre-cancer, a new study of a quarter million women in Australia demonstrated.

According to findings published in Papillomavirus Research, investigators evaluated the effectiveness of different doses of quadrivalent HPV vaccine by tracking instances of cervical intraepithelial neoplasia (CIN) 2 or 3/adenocarcinoma–in–situ (AIS)/cancer over a 7-year follow-up period.

Using data from all 8 jurisdictional cervical screening registers in Australia, along with the national HPV vaccination register, death index, and cancer registers, investigators compiled information on Australian women aged 15 years or under when eligible for the vaccine and screened between April 2007 and December 31, 2014. Results were adjusted a priori for age, socioeconomic status, and area of residence in order to estimate hazard ratios of histologically confirmed CIN2/CIN3/AIS/cancer.

The study population included 250,648 women (48,845 [19.5%] unvaccinated, 174,995 [69.8%] had received 3 doses, 18,190 [7.3%] 2 doses and 8618 [3.4%] 1 dose). Compared with unvaccinated women, the adjusted hazard ratio was significantly lower for all dose groups (1 dose 0.65 [95% Confidence Interval (CI), 0.52–0.81], 2 doses 0.61 [0.52–0.72] and 3 doses 0.59 [0.54–0.65]).

The adjusted hazard ratios for 1-dose and 2-dose recipients were comparable to the 3-dose recipients (1 dose 1.01 [95% CI, 0.81–1.26], 2 doses 1.00 [0.85–1.17]) after adjusting for age at vaccination among the vaccinated group.

“Our previous research, where we did a similar analysis of screening outcomes amongst women who were older at first vaccination, did not find that 1 dose worked as well,” Julia Brotherton, B Med, MPH, FAFPHM, PhD, GAICD, medical director of Population Health at the VCS Foundation in Melbourne and lead author of the study, told Contagion®. “This is probably because many women were already exposed to HPV prior to being vaccinated and women who only received 1 of 3 recommended doses were more likely to have risk factors for HPV infection. So it was really exciting to see these findings now that girls vaccinated at a young age are entering screening.”

Investigators concluded that 1-dose vaccination may be a viable strategy in the quest toward eliminating cervical cancer.

“If only 1 dose is needed it would be easier for everyone and the problems with forgetting and needing to find the time to have the second and third doses will cease,” Brotherton said. “It will be cheaper and will make the vaccine supply—which is currently limited so sadly directly preventing the protection of girls in resource poor settings—go much further. It could open the way to mass 1-dose campaigns.”

Brotherton advised clinicians to continue following current HPV vaccination recommendations (2 doses 6 months apart if aged 15 or under at first dose, and otherwise 3 doses) pending the results of randomized 1-dose trials currently underway. 
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