Potential impact of a nonavalent HPV vaccine on the occurrence of HPV-related diseases in France

Based on large number of cases, the national multicentre EDiTH studies previously reported the HPV genotype distribution for different cervical, anal, or oropharyngeal diseases in France [14-20]. Assuming a 100% vaccine efficacy and vaccination coverage, the EDiTH results suggested that a 6/11/16/18 quadrivalent HPV vaccine could prevent between 70% and 83% of ICC and anal cancer cases.

The attribution of cases to HPV types is often complicated by the existence of multiple infections characterized by the presence of several HPV types in the same tumor. Therefore, the potential benefit of an HPV vaccine is difficult to assess especially when HPV types not targeted by the vaccine are present. In all EDiTH studies and in the present study as well, we thus calculated a low and a high estimate of the vaccine impact based on presence of single or multiple infections. It is possible that the high estimate gives an overestimation of the potential impact of the vaccine since one assumes that HPV types targeted by the vaccine are causally related to the lesion in which they are found even in the presence of another HPV type. It is thus reasonable to believe that the “true” potential impact lies somewhere between the low and the high estimates.

If low estimate calculations are considered, the present study indicates that the absolute additional impact of a nonavalent vaccine is highest for CIN2/3 with a 33% increase in the proportion of cases targeted by the nonavalent vaccine. This additional benefit is intermediate for ICC (15% increase), LSIL (12%) and anal cancer (10%) whereas almost no additional benefit is observed for genital warts (5%) and oropharyngeal carcinomas (0%). The EDiTH II study showed that between 43% and 65% of CIN2/3 cases were associated with HPV 6/11/16/18 (low and high estimates) [15] whereas the present study indicates that a nonavalent vaccine could target 77% and up to 90% of all CIN2/3 cases. This benefit on the prevention of CIN2/3 cases could have a real public health impact by reducing the costs related to the management of these lesions. It is indeed estimated that 25,000 to 30,000 conizations are performed in France annually [21]. The benefit on ICC would also be substantial with up to 92% of ICC cases that could be targeted by a nonavalent vaccine. Even if the proportion of LSIL cases attributed to HPV 6/11/16/18 was rather low (14-34%), the proportion of cases associated with HPV types targeted by the nonavalent vaccine is increased by almost 90% (14% vs 26% considering the low estimates). However, for genital warts, only about 5% of cases are attributed to the additional HPV types found in the nonavalent vaccine (HPV 31/33/45/52/58) resulting in a low efficacy benefit. Similarly, no oropharyngeal carcinoma case was associated with these additional HPV types suggesting no additional benefit of a nonavalent vaccine in this group. This limited additional benefit on oropharyngeal carcinoma and genital warts is mainly explained by the fact that these conditions are almost exclusively associated with HPV types targeted by the bivalent or quadrivalent vaccines. Anal cancers are known to be mainly associated with HPV 16. A possible explanation for the observed additional benefit of the nonavalent vaccine (15%) is that we included some HIV positive patients (14%) with higher risk of multiple infection (50% vs 20% in HIV negative patients).

It should be noticed that a strong epidemiological impact characterized by significant reductions in HPV-related precancerous lesions and cancers may be achieved only if vaccination coverage reaches more than 80% [22]. However, by the end of 2013, the vaccination coverage with 3 doses reached only 20% of 16 year-old women in France [23]. By raising public awareness of the importance of HPV vaccination, general practitioners and gynecologists have to play an important role for increasing vaccination coverage.

A possible limitation of the present study is that HPV positivity in the EDiTH studies was based on HPV DNA detection only which could have resulted in a slight overestimation of the proportion of cancers potentially attributed to HPV. This is particularly true for oropharyngeal carcinomas for which HPV RNA detection would be a more accurate marker for those related to HPV infection. Moreover, other risk factors such as smoking or alcohol abuse are possibly involved. We calculated low and high estimates with the aim of taking into account the lack of knowledge regarding the causal relationship between each lesion and multiple HPV infection types. Low estimates suppose that the vaccine only prevents cases with genotypes targeted by the vaccine, while high estimates rather suppose that the vaccine prevents all cases where at least one genotype targeted by the vaccine is present, even in the presence of another genotype. This assumes that the other genotype is not involved in the occurrence of the lesion. Of course, true effects are in-between and it should be noted that alternative methods based on proportional (i.e., weighted) or hierarchical attributions of genotypes to disease categories have been proposed, providing intermediate estimates [10,24,25]. We nevertheless preferred to report estimates intervals rather that single estimates.

However, our results are in accordance with previous results reporting that a nonavalent vaccine would increase the protection from 70% to almost 90% of the infections responsible for ICC [13]. Moreover, a model-based analysis showed that at the population level, the switch from a bivalent or a quadrivalent to a nonavalent vaccine would further reduce the occurrence of precancerous lesions and cervical cancer [26].

In France, both the bivalent and the quadrivalent vaccines are available with a predominant use of the quadrivalent [27]. Gardasil is currently indicated for the prevention of premalignant genital lesions (cervical, vulvar and vaginal), premalignant anal lesions, cervical cancers, anal cancers, and genital warts (condyloma acuminata) causally related to specific HPV types [28]. It should thus be borne in mind that the potential vaccine impact we assessed is hypothetical and concerns some outcomes (e.g. oropharyngeal carcinoma) for which no specific indication exists yet.

Pap smear screening is and will remain a very efficient tool for the prevention of ICC. Even if screening of elderly women should still be highly recommended, HPV vaccination could reduce and hinder the spread of the virus and prevent HPV-related diseases and cancers for which no screening strategies are available.