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“Extremely reassuring” studies back up vaccine safety assurances

“Extremely reassuring” studies back up vaccination safety assurances - Featured Image

Patients can be reassured about vaccine safety on the basis of two large studies that have directly tested claims about the potential harms of the human papillomavirus (HPV) and pertussis vaccines.

The first study, published in the journal Pediatrics this month, found no association between HPV vaccination and primary ovarian insufficiency (POI) among almost 200,000 female patients enrolled in the Kaiser Permanente health system in Oregon and Washington.

Claims of a link between HPV vaccination and POI have circulated widely on the internet on the basis of published case series. These include a case published in BMJ Case Reports in 2012 of a 16-year-old Australian girl whose menstrual cycle became scant and irregular following vaccination.

The report prompted a statement from the Therapeutic Goods Administration at the time saying there was no “plausibly biological basis” for the link.

Latest HPV vaccine study “extremely reassuring”

Now Associate Professor Julia Brotherton, medical director of registries and research at the Victorian Cytology Service Registries said the latest study was “certainly significant and extremely reassuring”.

Out of 199,078 female patients aged 11 to 34 – 58,871 of whom received the HPV vaccine in adolescence – the study found 33 probable and 13 possible cases of primary ovarian insufficiency after follow-up averaging five years. Only one of the cases was vaccinated against HPV before symptom onset; a 16-year-old who received her third dose of HPV vaccine almost two years before estimated symptom onset.

This time lag was “not consistent with the authors of case reports who observed onset within 12 months of vaccination”, the authors noted.

They added: “although we did not formally test, we did not observe any temporal clustering of vaccine exposures among patients”.

More than half of the confirmed POI cases were patients who were diagnosed at age 27 or older, and only one patient was diagnosed under the age of 15.

The study could not adjust for contraceptive use, which the authors noted may mask the symptoms and onset of POI.

Nevertheless, they concluded: “We found no evidence of increased risk of POI after HPV vaccination, or other routine adolescent vaccination exposures, in this population-based retrospective cohort study with nearly 200,000 young women…We believe this study should lessen concern surrounding potential impact on fertility from HPV or other adolescent vaccination.”

Pertussis vacccine not linked to autism

A second study in Pediatrics investigated the potential association between prenatal tetanus, diphtheria, acellular pertussis (Tdap) vaccination and autism spectrum disorder (ASD) risk in offspring, using data from Kaiser Permanente Southern California.

The study followed up 81,993 pairs of pregnant women and their children for up to 6.5 years after birth. Almost half had received the prenatal Tdap vaccine.

ASD was diagnosed in 1,341 children, and incidence was greater in the unvaccinated than the vaccinated group; 3.78 per 1000 person years in the Tdap exposed versus 4.05 per 1000 person years in the unexposed (HR: 0.98, 95% CI: 0.88-1.09).

The authors concluded: “Prenatal Tdap vaccination was not associated with an increased ASD risk. We support recommendations to vaccinate pregnant women to protect infants, who are at highest risk of death after pertussis infection.”