The human papilomavirus (HPV) vaccine is up to 20 times more likely than other school-based vaccines to cause anaphylaxis, according to a study released Monday.
Anaphylaxis is a severe allergic reaction. Symptoms include difficulty breathing, nausea and rashes, but can be treated easily if identified early.
Last year Ontario, Nova Scotia, Prince Edward Island and Newfoundland launched HPV vaccination programs in schools, and more provinces are slated to begin programs in September. The massive campaign has had some parents asking questions about the safety of the vaccine.
The Australian rate of anaphylaxis in women following HPV vaccination is 2.6 per 100,000 doses. For most other vaccines the rate is 1 per million.
Dr. Julia Brotherton, lead author of the study, published in the Canadian Medical Association Journal, said some women may be allergic to the vaccine components. So far researchers haven't found which parts of the vaccine are causing the reactions.
Brotherton and colleagues in Australia vaccinated 114,000 women between the ages of 16 and 18 in 2007. They found 12 suspected cases of anaphylaxis, and seven in which the allergic reaction was "quite severe."
However, she said none of the girls suffered any lasting health problems and the reactions shouldn't discourage people from getting the HPV vaccine, which helps prevent cervical cancer.
"I certainly don't believe this is a reason not to receive a vaccine against HPV. It can happen with any vaccine or medication so I would reassure parents this is not a reason not to have their child vaccinated," Brotherton said..
Brotherton said the risk of getting anaphylaxis is "very, very tiny" and the benefits of the vaccine are "overwhelming."
"I think it is a great step forward in the control of cancer," she said.
Support for vaccine reiterated
Dr. Noni MacDonald of the IWK Health Centre in Halifax wrote the CMAJ editorial accompanying the study.
"Cervical cancer has not disappeared in Canada," she said.
There are about 1,300 cases of cervical cancer expected this year and 300 deaths, she said.
"That is not trivial...The problem is this virus is out there in our community and you can get it anytime you have sexual intercourse."
MacDonald said Canadians should be reassured by the findings because they allow parents and those getting vaccinated to create an informed opinion.
Merck Frosst Inc., the company that manufactures the vaccine, known as Gardasil, released a statement welcoming the research.
"The need to monitor the vaccine following wide spread use is an important and necessary step to further understand the role of HPV immunization as a public health intervention," the statement read.
The HPV virus leads to 400,000 abnormal Pap smear results and 36,000 cases of genital warts annually, the release said. The vaccine is 96 to 100 per cent effective at preventing HPV types 6, 11, 16 and 18, which cause the most clinical diseases.
No allergic reactions in Canada
Since the vaccine's approval in July 2006, there have been more than half a million doses distributed in the country, according to the Public Health Agency of Canada.
The agency is aware of the possibility of anaphylaxis but so far there have been no confirmed reported cases after HPV immunization in Canada.
The vaccine is "safe and effective," the PHAC said.
Publicizing the study is a way of making people aware of the possible side effects of the HPV vaccine, so they will be prepared if an allergic reaction occurs, Brotherton said.
She stressed that all women planning to get the vaccine tell their doctor of any allergies. A reaction to a first dose can cause a more serious reaction in a second dose, she said.
"Your whole body is affected by the allergic reaction and there is the risk that the reaction can progress and eventually you can have difficulties breathing and your blood pressure can drop and it can be life threatening," she said. "So that is why it is important to raise awareness that this can happen."
If recognized quickly, anaphylaxis is easily treatable with adrenalin. Anyone giving the vaccinations should be fully trained to be able to recognize the symptoms, she said.
This is why doctors ask patients to stay in their office for at least 15 minutes after any vaccination. The greatest concern is if a patient doesn't stay in range of medical care after being vaccinated and has a reaction, Brotherton said.
"If they were driving or something they could actually faint and they could lose consciousness."
