The vaccine for cervical cancer that was developed for women in the United States is working in Canada, and its effectiveness is lower among vaccinated women, according to a new study.
“We know that women are more likely to be vaccinated with a vaccine against cervical cancer than vaccinated with other types of cervical cancer,” says senior author Liza Sibeko of the University of Calgary, who was not involved in the study.
“Our results suggest that HPV vaccination is protective in this population.
The vaccination of women with other kinds of cervical cancers is not as effective as the HPV vaccination for cervical cancers.”
Women with HPV-16 infections were more likely than those without to develop a high-risk pregnancy complication such as preterm birth or preterm delivery, or to have a low-risk complication such a low birth weight, Sibkeno says.
The study was published in the Journal of the American Medical Association.
Researchers used data from a nationwide birth registry, including a birth certificate, birth certificate information and other records, to track the vaccination status of 6.2 million women between 2003 and 2013.
They also analyzed data from the Ontario Centre for Child Health Monitoring, which collects data on health and welfare.
The study found that the vaccinated women had a lower risk of having preterm or low-birth weight births and a higher risk of preterm deliveries than those who had not been vaccinated.
The vaccinated women also had a higher rate of preemie deaths, Siba-Sangha says.
“Preterm birth rates are high among vaccinated patients and are a clear public health concern,” says study co-author Dr. Sibokeni.
“We can’t do anything about that, but we can make vaccination more effective in the general population.”
Preemie mortality rates in Canada have risen in recent years and have more than doubled since 2007.
“A high-dose vaccination can help reduce the risk of death during pregnancy, and the vaccine protects against cervical cancers, too,” Siba, who is also a professor of medicine at McMaster University, says.
The HPV vaccine is licensed by the Canadian and U.S. governments for use in men and women.
In Ontario, the federal government has granted approval for the HPV vaccine for use to women, as well as for men, pregnant women and women with pre-existing health conditions, as a preventive measure against HPV-19.
The vaccine, administered via a patch to women between 12 and 18 months old, protects against the three types of HPV: HPV16, HPV18 and HPV18-19, which cause the most cervical cancers.
The vaccine also helps to prevent infection with HPV16 and 16-18 and other types, and helps to reduce the symptoms of cervical abnormalities such as abnormal blood or pelvic pain.
The results also found that vaccinated women were less likely to have pelvic pain or discomfort during or immediately after the vaccination than those not vaccinated.
Siba says this finding is consistent with previous research showing that HPV vaccine protects women against both HPV types and pelvic pain, which can be associated with complications from cervical cancer.
The authors note that in their analysis, they didn’t adjust for differences in the vaccination regimen among women.
They did however adjust for a range of potential confounding factors, including ethnicity, family history of cervical or uterine cancer and age.
Sibkeni says the study also found the vaccinated group was less likely than the non-vaccinated women to be diagnosed with a pre-eclampsia-related condition.
That is, women who had the HPV16 vaccine had a 50 per cent lower risk for a preterm pregnancy, compared with women who didn’t have the vaccine, and for a low or low birthweight.
The researchers say their study could not prove causality, but it does provide some evidence that vaccination is an effective preventive measure.
“The HPV vaccination has the potential to reduce women’s risk of developing cervical cancer by as much as 40 per cent, so it is important to vaccinate as many women as possible,” Sibkonen says.
“There is still a lot we don’t know about this vaccine, but this is a great first step.”
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