26 Aug, 14 | by Leslie Goode, Blogmaster
Quadrivalent HPV vaccine (HPV4) has been shown to protect against HPV types 16 & 18, which cause 70% of cervical cancers, and HPV types 6 & 11, which cause 90% of genital warts. Health authorities in the US and elsewhere have therefore recommended routine vaccination of girls (and more recently boys) at ages 11 & 12, and “catch-up” vaccination for women aged 13 to 26. Vaccination programmes in New Zealand (STIs/Read & Fairley) and Australia (STIs/Fairley and Bradshaw) have indicated what can be achieved, given adequate coverage.
For the US and elsewhere there remains a problem of ensuring coverage. Recent figures from the US Centers for Disease Control and Prevention National Immunization Survey-Teen (NIS-Teen) for 13-17 year-olds ≥1 dose quadrivalent or bivalent vaccine, CDC/MMWR 25.7.14, show levels that remain obstinately low despite year on year improvement, rising from 53.8% to 57.3% (girls), and from 20.8% to 34.6% (boys) between 2012 and 2013. By comparison, UK uptake on the first 3 years of its programme was 66% (STIs/Sacks & Robinson). The low US rate is of particular concern because there is considerable evidence from the US and UK that it is often those who are most at risk, such as racial and ethnic minorities, who are most likely to miss out on vaccination (STIs/Niccola & Hadler; STIs/Sacks & Robinson; STIs/Liddon & Hadler). Tantalizingly, the Report estimates at 91.3% the coverage for ≥1 dose by age 13, if HPV vaccine had been administered to adolescent girls born in 2000 during health care visits when they received another vaccine.
This, of course, raises the question why this opportunity is being missed. The authors cite the disquieting datum that, when NIS-Teen asked parents to identify reasons for non-vaccination, one third of parents of girls and over half of parents of boys reported that their child’s clinician had not recommended that their child receive an HPV vaccination. They therefore point to the need to address gaps in clinician knowledge and communication skills as well as parental knowledge. A discussion of apparent difficulty of ensuring the conformity of providers to HPV guidelines has already been discussed by STIs/Kepka & Seraya.
Given poor levels of uptake at age 11-12, especially among some of the needier populations, it becomes important to know the effectiveness of catch-up vaccination and incomplete vaccination. This is made very evident in a recent US cross-sectional study, Brogly & Shi Yang (B&Y), of the relation of cervical abnormalities to HPV vaccination status amongst 235 minority women undergoing routine cervical cytology testing. Only 54% of these had initiated, and only 33% completed, vaccination – and of those vaccinated, only 3% had received the vaccination before sexual debut. Their results appear to show that even a tardy, and frequently incomplete, HPV vaccination confers significant benefits on individual women. Abnormalities (ASCUS, LSIL or HSIL) proved to be considerably reduced amongst the vaccinated group, even where participants had not completed the full course of three injections – RR 0.35 for ≥1 dose as against no vaccination; RR 0.45 for 1-2 doses as against no vaccination; RR 0.26 for completed vaccine as against no vaccination. If corroborated in further studies, these findings could reinforce argument in favour of the effectiveness of HPV catch-up against those have placed this in doubt (STs/Chesson & Markowitz).
The study also aimed to examine the relationship between vaccination status and HPV genotype, but the sample size was too small to establish anything very conclusive. STIs/Nielsen & Kjaer claim to demonstrate, with a far larger Danish sample, that low-risk types are frequent in ASCUS lesions, but scarcely ever occur in isolation from high-risk HPV types, where the lesions are more severe.