HPV16 harder to eliminate than other genotypes
The HPV16 genotype as well as associated cancers was more difficult to eliminate than other genotypes, according to findings from a modeling study.
“Currently licensed virus-like particle vaccines against HPV are nearly 100% efficacious in the prevention of infection from vaccine targeted HPV types,” Silvia Franceschi, MD, of the International Agency for Research on Cancer, and colleagues wrote. “In a sexually transmitted infection, such as HPV infection, herd protection is governed by the probability of infection transmission, the duration of the infection and sexual activity pattern, which varies in different populations. As a result, overall effectiveness of HPV vaccination at a population level, that is the sum of vaccine efficacy and herd protection, is population specific and, within the same population, typespecific.”
The researchers calibrated a dynamic transmission model with cervical screening data on patients from Italy, simulating a population that had gender and sexual behavior characteristics similar to those of various high-income countries. Franceschi and colleagues estimated the effectiveness of HPV vaccination against HPV16 and HPV45 infection, assuming a vaccine efficacy of 95% or less.
HPV45 showed a smaller basic reproductive number than HPV 16, resulting in better vaccine effectiveness and stronger herd protection for HPV45, the researchers reported (2.1 vs. 4). Among women aged younger than 35 years, the largest difference in infection prevalence occurred when Franceschi and colleagues simulated a 70% coverage rate in a girls-only vaccination program (99% for HPV45 vs. 83% for HPV16; herd protection, 37% vs. 16%).
In projections of gender-neutral vaccination programs, the largest difference occurred at 40% coverage, the researchers wrote (herd protection, 54% for HPV16 vs. 28% for HPV45).
Researchers wrote that at coverage of 80% or more, cross-protection of just 50% would reduce the prevalence of HPV45 by 94%.
Franceschi and colleagues noted that the findings highlighted the role of herd protection in eliminating HPV.
“In conclusion, the characteristics of individual [risk] HPV types strongly influence herd immunity and determine the level of coverage and type-specific vaccine efficacy (including cross-protection) that are required to reduce or eliminate the infection through HPV vaccination,” the researchers wrote. “Our findings are particularly relevant to low [or] middle income countries that are especially challenged by programmatic difficulties and variations in the cost of vaccines according to the number of targeted types.” – by Andy Polhamus
Disclosure: Franceschi reports no relevant financial disclosures. Please see the full study for a complete list of all other researchers’ relevant financial disclosures.