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HPV/Genital Warts Health Center

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Late Doses of HPV Vaccine May Still Be Effective

Study: Girls Still Get Protection When Shots Are Given Months Later Than Recommended

Comparing HPV Vaccine Schedules continued...

More than 800 girls completed all three doses, and researchers gave them blood tests after each shot to measure levels of antibodies against two cancer-causing HPV strains.

Compared to girls who got their doses on the recommended six-month timetable, researchers found that girls on the 9- and 12-month dosing schedules had only slight dips in their antibody levels, which weren’t expected to be clinically meaningful.

Girls who got their shots over two years had significantly lower antibody levels than the six-month group. But Neuzil points out that even those levels were still higher than have been seen in other studies of older teens and college-aged women. That suggests that spreading the shots over years may still shield girls from the cancer-causing virus.

Neuzil acknowledges, however, that nobody knows the magic number for antibodies against HPV. “We don’t know what level of antibody protects.”

Side effects in the study were mostly mild, with many girls complaining that their arms were sore after the shots. About 1% complained of more serious reactions, including weakness, nausea, and vomiting.

The study was funded by the Bill and Melinda Gates Foundation. Drugmaker Merck provided the vaccine doses.

The study is published in TheJournal of the American Medical Association.

A Case for Flexible HPV Vaccine Schedules

“We know we have trouble getting adolescents vaccinated,” says Lauri Markowitz, MD, team lead for epidemiology research in the division of STD prevention at the CDC. “They don’t go to the doctor’s office as often as young children do. It’s challenging to get them to finish on time.”

Though the official schedule is still a shot at 0, 2, and 6 months, public health authorities have acknowledged that there’s some flexibility with that time frame.

“Right now, we recommend that if someone’s late for a vaccine dose, it doesn’t need to be repeated, you just complete the schedule,” says Markowitz.

And there are two studies, one funded by the CDC and the other funded by National Institutes of Health, that are testing later dosing schedules to see how far the timeline can be stretched, especially between the second and third shots.

“We’re starting to build a case for more flexible schedules,” Neuzil says.

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