CALGARY, ALTA. As an epidemiologist whose research focuses on the prevention of cervical cancer, Dr. Eduardo L. Franco spends a lot of time arguing with health care professionals and patients who say that more research is needed before universal human papillomavirus vaccination can be recommended worldwide.
"Although clinical experience has just passed 6 years, the evidence base is one of the strongest in disease prevention," Dr. Franco said at the annual meeting of the Society of Obstetricians and Gynaecologists of Canada. "The standard of proof is far more rigorous than that used in the evaluation of candidate vaccines of the past."
Dr. Franco, director of the division of cancer epidemiology at McGill University, Montreal, shared several examples of arguments against HPV vaccination that he encounters, followed by his counterargument for each.
One chief argument he hears is that the vaccine is too costly and unaffordable where it's most needed. However, he said, procurement programs such as the Centers for Disease Control and Prevention's Vaccines for Children Program and the Pan American Health Organization's revolving fund should help to lower the cost. "Historically," he added, "prices decline with time since deployment."
In addition, ongoing studies of simplified schedulessuch as administering two doses instead of threemay affect price. Other common arguments against HPV vaccination include the following:
▸ There are no data on long-term duration of protection. In fact, to date, studies demonstrate a sustained antibody response with no indication that humoral immunity will wane before 10 years. "Even with lowered antibody titers, postvaccination protection has continued unabated," said Dr. Franco, who also is a professor of epidemiology and oncology at McGill.
▸ Protection is limited; vaccines cover only two oncogenic types. In fact, protection is against the two most important types (HPV 16 and 18), which translates into a protective fraction of 70% of all cervical cancers that "is likely to be expanded via cross-protection," he said.
▸ Screening will continue to be needed. True, Dr. Franco said, but recent progress on new technologies such as HPV testing with Pap triage "will permit extending screening intervals safely and cost effectively."
▸ There is a risk of type replacement, which occurred with the pneumococcal vaccine. Type replacement is unlikely to occur because there is no epidemiologic proof that HPV types compete for specific niches. "Several studies have tested this hypothesis," he noted.
▸ We should not vaccinate preteens and teens; there are no efficacy data on patients aged 9-14 years. "Immunobridging" studies show that vaccine-induced humoral response in preteens is the highest among all groups, "which is sufficient justification for expectation of benefit," he said.
▸ There is no proof yet that vaccination can reduce the risk of invasive cancers. Dr. Franco counters this notion by pointing out that absence of evidence is not evidence of absence.
Dr. Franco disclosed that his entire research program has been funded by the Canadian Institutes of Health Research (CIHR), the National Cancer Institute of Canada, and the National Institutes of Health. He has served as an occasional adviser to several companies with products related to cervical cancer prevention.
'Even with lowered antibody titers, postvaccination protection has continued unabated.' DR. FRANCO