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How was the HPV vaccine tested?

Over 10 million doses of the new HPV vaccine, Gardasil 9, have been given in the US in the past year. Gardasil 9 was studied in more than 13,000 females and males before it was registered for use.

The original HPV vaccine (Gardasil) was tested on more than 20,000 females in 33 countries and 4,000 males in 18 countries before it was approved for use. It is approved for females aged 9 to 45 years and males 9 to 26 years.

The trials did not seek to prove that the vaccine prevents cervical cancer. This is because it would not have been ethical to allow cervical cancer to develop in the group who did not receive the vaccine in the trials (the placebo or control group).

However the original trials showed that the vaccine is almost 100% effective in preventing abnormalities in cells in the cervix caused by cancer-causing HPV types 16 and 18. These abnormalities are a proven pre-cursor to cervical cancer.

Clinical trials of Gardasil involving more than 4,000 males aged 16 to 26 years from 18 countries showed the vaccine was 90% effective against HPV types 6, 11, 16 and 18 that cause genital warts and penile lesions, and 78% effective against HPV types 6, 11, 16 and 18 that cause anal lesions in men.

The trials of Gardasil 9 demonstrated that this vaccine is also almost 100% effective at preventing these cell abnormalities in the cervix caused by cancer-causing HPV types 31, 33, 45, 52 and 58.  

For ethical reasons, younger girls were not included in the trials as they would have been required to have regular Pap tests (now known as Cervical Screening Tests), which would have been inappropriate given their age. Younger boys were also excluded from the trials.

Instead, studies compared the body's immune response to the vaccine between younger and older girls, and younger and older boys. It was determined those younger girls and boys who received the vaccine in these studies:

  1. Experienced no increased adverse reactions to the vaccine compared to older girls and boys.
  2. Created more antibodies in response to the vaccine than older girls and boys. It is because of the high antibody levels that the HPV vaccine was tested in two doses rather than three in people aged 14 and under. The tests showed that the immune response from two doses is just as good in those aged 14 and under as the response after three doses in people aged 15 and over.

 

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Trials showed that the vaccine is almost 100% effective in preventing abnormalities in cells in the cervix caused by seven cancer-causing HPV types.

Design and partial content reproduced with the kind permission of the New Zealand Ministry of Health.

The HPV vaccine is a prescription medicine. Medicines have benefits and risks. After reading this website, talk to your doctor about the benefits and risks of this vaccine and to check eligibility.

Females who have had the HPV vaccine still need regular Cervical Screening Tests.