Women in a clinical study who became pregnant after being vaccinated against human papillomavirus (HPV) had no higher risk of miscarriage compared to women who were not exposed to the vaccine , according to a new analysis of additional data from a study Clinical trial carried out in Costa Rica.
The observational study, which was carried out by researchers in Costa Rica and the National Cancer Institute, appeared on Sept. 7 in the British Medical Journal.
The study evaluated the efficacy of a vaccine manufactured by GlaxoSmithKline which is now marketed under the name Cervarix. This vaccine is known as a bivalent HPV vaccine because it protects against infection by two types of HPV, 16 and 18. Together, these types cause the majority (about 70%) of cervical cancers and other anogenital cancers and Head and neck.
The Food and Drug Administration has approved three vaccines to protect against infection by HPV types that can cause cancer. Because vaccines can be applied to women of reproductive age, could worry any effects of HPV vaccines on the ability to complete the pregnancy.
In the new analysis, the researchers evaluated the risk of abortion among about 10,000 young adult women who participated in the NCI HPV Vaccine Study in Costa Rica as well as the extent of follow-up study. In the clinical study, about 7500 women had been randomly assigned to receive the bivalent HPV vaccine or a control vaccine (the hepatitis A vaccine). The study investigators also looked at pregnancy outcomes in a group of more than 2800 unvaccinated women who did not participate in the original randomized study.
Sequel to a previous result
The analysis focused on pregnancies conceived within 90 days of the vaccine in order to respond to a concern that emerged in 2010 by the safety monitoring board of the study data which was based on information from a different study. A combined analysis of two studies found no evidence to support a higher risk of miscarriage for pregnancies conceived at least 90 days after vaccination with the bivalent HPV vaccine.
However, researchers observed a possible increase in the rate of miscarriages in pregnancies conceived within 90 days of HPV vaccination compared to the control group. Although this finding was not statistically significant, the study authors could not exclude the possibility of a small increase in risk among pregnancies conceived within 3 months of vaccination.
In the new study, statistical analysis of the data indicated that the risk that a pregnancy conceived within 90 days of the vaccination ending in an abortion was not greater than the risk of an abortion among women who did not receive the HPV vaccine. Similarly, the risk of miscarriage among pregnancies conceived at any time after HPV vaccination was no greater than that among unvaccinated women.
However, in a subgroup analysis, there was an indication of a small increase (less than 1%) in the absolute risk of miscarriage in the second trimester for women vaccinated.
“Given the lack of a pathophysiological mechanism established which could explain the result of the subgroup may be due to the role of luck in statistical analysis , ” said lead study author Dr. Orestis Panagiotou, of the Division of Epidemiology and Cancer Genetics of NCI, who added that there are no reports of this association in the scientific literature. However, since it is not possible to rule out a genuine association, the authors suggested that this result should be further explored in future studies.
Support for reassurance
The researchers indicated that the new results should not be applied outside the bivalent vaccine. HPV vaccines are not recommended for pregnant women.
In an interview given a few weeks before his recent death, Dr. Sholom Wacholder, who conducted the first safety analysis in 2010 as the lead statistician for the NCI study, said the new findings “provide stronger evidence and reassurance” about the lack of a risk of abortion associated with bivalent HPV vaccine.
“The results also support safe follow-up with HPV vaccination programs as recommended by groups such as the Advisory Committee on Immunization Practices of the Centers for Disease Control, the World Health Organization and program promoters in the countries, “added Dr. Wacholder.
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