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Lancet Infect Dis. 2014 Oct;14(10):958-66. doi: 10.1016/S1473-3099(14)70841-2. Epub 2014 Aug 5.

Assessment of herd immunity and cross-protection after a human papillomavirus vaccination programme in Australia: a repeat cross-sectional study.

Author information

1
Regional World Health Organization Human Papillomavirus Laboratory Network, Department of Microbiology and Infectious Diseases, The Royal Women's Hospital, Parkville, VIC, Australia; Department of Obstetrics and Gynaecology, University of Melbourne, Parkville, VIC, Australia; Department of Microbiology, Royal Children's Hospital, Parkville, VIC, Australia; Murdoch Childrens Research Institute, Parkville, VIC, Australia. Electronic address: sepehr.tabrizi@thewomens.org.au.
2
National HPV Vaccination Program Register, Victorian Cytology Service, East Melbourne, VIC, Australia; Sydney University Discipline of Paediatrics and Child Health, Children's Hospital Westmead, Sydney, NSW, Australia.
3
The Kirby Institute, University of New South Wales, Sydney, NSW, Australia.
4
Sydney University Discipline of Paediatrics and Child Health, Children's Hospital Westmead, Sydney, NSW, Australia.
5
School of Public Health and Community Medicine, University of New South Wales, Sydney, NSW, Australia.
6
Family Planning New South Wales, Ashfield, NSW, Australia.
7
Family Planning Victoria, Box Hill, VIC, Australia; Department of Obstetrics and Gynecology, Monash University, Clayton, VIC, Australia.
8
Family Planning Western Australia, Northbridge, WA, Australia.
9
Regional World Health Organization Human Papillomavirus Laboratory Network, Department of Microbiology and Infectious Diseases, The Royal Women's Hospital, Parkville, VIC, Australia; Murdoch Childrens Research Institute, Parkville, VIC, Australia.
10
National HPV Vaccination Program Register, Victorian Cytology Service, East Melbourne, VIC, Australia.
11
Regional World Health Organization Human Papillomavirus Laboratory Network, Department of Microbiology and Infectious Diseases, The Royal Women's Hospital, Parkville, VIC, Australia; Department of Obstetrics and Gynaecology, University of Melbourne, Parkville, VIC, Australia; Department of Microbiology, Royal Children's Hospital, Parkville, VIC, Australia; Murdoch Childrens Research Institute, Parkville, VIC, Australia.

Abstract

BACKGROUND:

After the introduction of a quadrivalent human papillomavirus (HPV) vaccination programme in Australia in April, 2007, we measured the prevalence of vaccine-targeted and closely related HPV types with the aim of assessing direct protection, cross-protection, and herd immunity.

METHODS:

In this repeat cross-sectional study, we recruited women aged 18-24 years who attended Pap screening between October, 2005, and July, 2007, in three major metropolitan areas of Australia to form our prevaccine-implementation sample. For our postvaccine-implementation sample, we recruited women aged 18-24 years who attended Pap screening in the same three metropolitan areas from August, 2010, to November, 2012. We compared the crude prevalence of HPV genotypes in cervical specimens between the prevaccine and the postvaccine implementation groups, with vaccination status validated against the National HPV Vaccination Program Register. We estimated adjusted prevalence ratios using log linear regression. We estimated vaccine effectiveness both for vaccine-targeted HPV types (16, 18, 6, and 11) and non-vaccine but related HPV types (31, 33, and 45).

FINDINGS:

202 women were recruited into the prevaccine-implementation group, and 1058 were recruited into the postvaccine-implementation group. Crude prevalence of vaccine-targeted HPV genotypes was significantly lower in the postvaccine-implementation sample than in the prevaccine-implementation sample (58 [29%] of 202 vs 69 [7%] of 1058; p<0·0001). Compared with the prevaccine-implementation sample, adjusted prevalence ratios for vaccine-targeted HPV genotypes were 0·07 (95% CI 0·04-0·14; p<0·0001) in fully vaccinated women and 0·65 (0·43-0·96; p=0·03) in unvaccinated women, which suggests herd immunity. No significant declines were noted for non-vaccine-targeted HPV genotypes. However, within the postvaccine-implementation sample, adjusted vaccine effectiveness against vaccine-targeted HPV types for fully vaccinated women compared with unvaccinated women was 86% (95% CI 71-93), and was 58% (26-76) against non-vaccine-targeted but related genotypes (HPV 31, 33, and 45).

INTERPRETATION:

6 years after the initiation of the Australian HPV vaccination programme, we have detected a substantial fall in vaccine-targeted HPV genotypes in vaccinated women; a lower prevalence of vaccine-targeted types in unvaccinated women, suggesting herd immunity; and a possible indication of cross-protection against HPV types related to the vaccine-targeted types in vaccinated women.

FUNDING:

Australian National Health and Medical Research Council and Cancer Council Victoria.

PMID:
25107680
DOI:
10.1016/S1473-3099(14)70841-2
[Indexed for MEDLINE]

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