A group of Canadian public health professionals says there remain a number of unanswered questions about the HPV vaccine and that a universal vaccination program in Canada "is premature and could have unintended negative consequences."

Abby Lippman, a professor of epidemiology at McGill University, and colleagues, conducted a review of the current literature on the HPV the vaccine and summarize their conclusions in an editorial in the Canadian Medical Association Journal.

They found that while it appears that the vaccine is highly effective in preventing infection with HPV types 16 and 18 (currently thought to be the cause of about 70% of cervical cancer cases), it's still not clear whether reducing such infections will translate into fewer cervical cancer deaths in the long run.

They note that rates of deaths from cervical cancer had been dropping in Canada for years anyway, because of the widespread availability of publicly-funded programs for Pap smear testing.

They also note that there are many gaps in knowledge about the vaccine:

• It's not clear for how long the vaccine will be effective;
• or whether a booster shot will be needed in later years;
• and there is also a lack of data, they say, on the effectiveness of the HPV vaccine when given at the same time as other immunizations.

They also wonder whether a mass HPV vaccination program will lead to reductions in safer sex practices and Pap screening rates.

And they note that relatively few girls aged 9 to 15 years were enrolled in the clinical trials of Gardasil and the youngest of whom were followed for only 18 months. Yet girls in this age group represent the priority target population for mass vaccination.

And, they note, all of the reported HPV vaccine trials, whether of Gardasil or its potential competitor Cervarix, were funded in whole or in part by the vaccine's manufacturer.

Noting that Gardasil is the most expensive childhood vaccine proposed for mass use (it currently costs $404 for the 3 required doses), the authors point out that there haven't been any cost-effectiveness analyses to determine whether the proposed vaccination programs will result in fewer cancer deaths.

The authors provide some general recommendations for the development of a mass HPV vaccination program, including a call for government to educate the public about the realities of cervical cancer, HPV infection and HPV vaccinations, and to support unbiased research to collect the data now missing.

"It is time to take a breath and reflect on what we know and what we don't know, and to develop a plan based on solid, reliable evidence that adds value for everyone," the authors write.

"Individual girls and women, as well as policy-makers, can make truly informed decisions about vaccinations only when they have all the evidence, and today, there are more questions than answers."