<![CDATA[Systematic review of studies on HPV type-replacement after generalized vaccination]]>

Dr. David Mesher presented results of by far the largest meta-analysis on type-replacement following HPV vaccination.

The study initially identified 4219 unique reports comparing type-specific HPV prevalence before and after the introduction of the HPV vaccination program [1]. Out of these, nine studies reported type-specific HPV prevalence pre- and post-vaccination in 16 to 19 year-old and in 20 to 24 year-old females. The meta-analysis included studies conducted in countries using either the bivalent HPV16/18 vaccine (three studies) or the quadrivalent HPV6/11/16/18 vaccine (six studies). The populations comprised three studies conducted among women attending for chlamydia screening (25,151 samples), two studies conducted in women attending for cervical screening (6,575 samples), two population-based surveys (4,124 samples) and two in women attending a primary care clinic (973 samples). Altogether, type-specific HPV prevalence data was available from 36,823 study participants.

For the non-vaccine HPV types the combined (both vaccines included) pre- vs. post-vaccination comparisons revealed evidence of a reduced prevalence for HPV31 in both age-categories, but little evidence for reductions in HPV33 or HPV45. There was some evidence of an increased prevalence for HPV39 (figure 1), and to a lesser extent for HPV 52, 58 and 73 although results were inconsistent between age-groups.

In conclusion, the meta-analysis verified vaccine induced cross-protection against HPV31 for both the bivalent and the quadrivalent HPV vaccine. It did not provide clear-cut evidence of HPV type-replacement as data was unclear about whether changes in other non-vaccine types are due to changes in study populations or possible unmasking of non-vaccine types with low viral load. The effect of differential vaccination coverage as a source of heterogeneity could not be assessed due to the relatively small number of studies included in the meta-analysis.

The meta-analysis verified vaccine induced cross-protecion against HPV31 for both the bivalent and quadrivalent HPV vaccine. It did not provide clear-cut evidence of HPV type-replacement

Prevalence ratios were not calculated if there was evidence of heterogeneity of data (I² value ≥25%). For HPV 39, borderline increases in prevalence were observed after the vaccination campaign. Adapted from [1].

Figure 1.

Prevalence ratios and 95% CI for HPV35, HPV39 and HPV51 comparing pre- and post-vaccination periods in young women.

References
1. Mesher D, Soldan K, Lehtinent, et al. Population- Level Effects of Human Papillomavirus Vaccination Programs on Infections with Nonvaccine Genotypes. Emerg Infect Dis. 2016 Oct; 22(10): 1732–1740.

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David Mesher, MD
Public Health England
London, England
d.mesher@phe.gov.uk

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