After more than 23 million doses of HPV vaccine administered to young women in the United States, a mere 12,424 adverse reactions have been reported, according to a new study.
The research, published in today's edition of the Journal of the American Medical Association, found that the vast majority of those reactions were "non-serious," principally fainting, soreness and rash at the vaccine site, and headaches.
But the detailed data from the U.S. Centers for Disease Control and Prevention (CDC) also show that 772 of the young women reported serious health problems after receiving the HPV vaccine, including anaphylaxis (life-threatening allergic reaction), blood clots, pancreatic failure and motor neuron disease.
There were 32 deaths reported among those who received the vaccine. The young women died anywhere from two to 405 days after receiving the vaccine, and many had underlying health conditions.
Barbara Slade of the CDC immunization safety office and principal author of the paper, said the data "must be interpreted cautiously and cannot generally be used to infer causal association."
In other words, the rates of severe illness and death are similar among those who have been vaccinated and those who have not, meaning the HPV vaccine was not necessarily fully or partly responsible for those health problems.
Eduardo Franco, a professor of epidemiology at McGill University in Montreal, said it more bluntly: "These deaths and severe illnesses were not caused by the vaccine - they would have happened anyway."
He also expressed concern that the numbers will be used to foment fear by those who oppose HPV vaccination. "This vaccine is as safe - if not safer - than all the other vaccines out there," Dr. Franco said.
There are no comparable Canadian data.
Health Canada's adverse drug reaction database has no entries for the HPV vaccine, Gardasil.
In the U.S., there are two HPV vaccines available, sold under the brand names Gardasil and Cervarix. They protect against infection with some strains of human papillomavirus that are responsible for about 70 per cent of cervical cancers, and for the majority of genital warts.
Vaccination, however, has proved controversial.
"The theory behind the vaccine is sound: If HPV infection can be prevented, cancer will not occur," Charlotte Haug, editor-in-chief of The Journal of the Norwegian Medical Association writes in an editorial also published in today's edition of JAMA. "But in practice the issue is more complex."
She said the relationship between infection with HPV at a young age and development of cervical cancer 20 to 40 years later is not clear. In fact, almost all HPV infections are cleared by the immune system, and it is currently impossible to predict who will end up with cervical cancer and why.
As a result, Dr. Haug said, the benefit of the HPV vaccine remains uncertain and the new data on adverse events only add to the uncertainty.
Dr. Franco said it is true that HPV vaccine will not prevent a lot of cases of cervical cancer in countries, such as Canada and the U.S., that have excellent Pap screening programs.
However, the vaccine will prevent the development of a lot of precancerous lesions that cause women pain and grief.
In Canada, HPV vaccines are recommended for all girls and women aged 9 to 26, and the vaccine is offered to pre-teen and teenaged girls free of charge in school-based programs in all 13 provinces and territories.