Prevalence data will help assess trends, tailor screening
In a related study, investigators led by Dr. Warner K. Huh, a professor in the department of obstetrics and gynecology at the University of Alabama at Birmingham, determined the relative prevalence of HPV genotypes in the U.S. population.
Susan London/Frontline Medical News
Dr. Warner K. Huh
“We are going to see a transition from the quadrivalent vaccine to the 9-valent vaccine, so information regarding genotypes in this country becomes extremely important,” he said. “There is very limited information in terms of the HPV prevalence for genotypes across the U.S. and more importantly, we almost have zero information on what that prevalence is in a low-risk population. To understand changes in the prevalence in this country, particularly with vaccination and then ultimately as it relates to screening, you are going to need to understand what that baseline data is.”
The investigators analyzed data from 46,751 women aged 21 years or older in the ATHENA study (Evaluation of the Cobas 4800 HPV Test for the Detection of High-Grade Cervical Disease), the largest HPV screening cohort nationally. The Roche-funded study was used to gain Food and Drug Administration approval for primary HPV screening in the United States. Less than 3% of enrolled women had received an HPV vaccine.
The women had HPV testing, in addition to liquid-based Pap testing and colposcopy, with follow-up out to 3 years in a subset. Genotyping was used to detect 16 high-risk types of HPV (16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, 66, 68, 73, and 82), and the prevalence of each was benchmarked to that of HPV 16.
“We benchmarked to HPV 16 for a couple of reasons,” Dr. Huh explained. “One of which is that we now have two vaccines – the quadrivalent and the 9-valent vaccines – and we thought it would be interesting to see what happens to that ratio as we have had one for essentially 10 years and the other one transitions in. The other reason, of course, is that it’s a highly prevalent type and a type that’s seen in both vaccines.”
Results showed that the absolute prevalence of all 16 types combined was 11.5% in the entire cohort and 10.0% in the low-risk subset with normal Pap results. In age-stratified analyses, it was higher among women aged 21-24 years than among older women.
The prevalence ratio relative to HPV 16 for the most common viral types among those assessed ranged from 0.12 for HPV 33 to 0.57 for HPV 52.
“The ratios may not be relevant to you today, but they may become highly relevant 10, 20, or 30 years from now,” Dr. Huh commented, discussing HPV type 31, which had a ratio of 0.43, as an example. As coverage by the quadrivalent vaccine and hence protection against type 16 rises, “what we would expect over the next 10 years is that ratio to increase substantially, some theorize as much as fourfold. Then as you roll out the 9-valent vaccine, theoretically, that ratio should normalize back to 0.43, assuming again that the efficacy is equivalent for [type 31] and for type 16,” he explained. “So this is where it becomes very interesting, because if it doesn’t, there is something else going on in the population.”
The new data additionally allow good ability to track the phenomenon of viral type replacement, Dr. Huh said.
“But most importantly, what it allows us to do is to look at screening and the impact of the nonavalent vaccine on screening in the United States. If you all buy into primary HPV screening, the current algorithm uses type 16 and type 18. Well, if type 16 and type 18 go away and these ratios change, then we need to seriously revisit how we do primary HPV screening because the current algorithm is probably not the right algorithm to use,” he maintained.