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When less is more: A single dose of HPV vaccine works as well as two, WHO finds

The vaccine that protects people against most cervical cancers elicits an immune response so potent that just a single dose is enough, according to the World Health Organization.

A Assessment in April by WHO’s Strategic Advisory Group of Experts on Immunization concluded that one dose of human papillomavirus (HPV) vaccine “provides solid protection against HPV,” similar to the two-dose schedule most adolescents in Australia currently receive.

The WHO recommended countries update their vaccination schedules accordingly

And in some parts of the world, the wheels are already moving.

In February, the UK Vaccine Advisory Committee has issued advice to change the HPV vaccine schedule to a single dose for children under 14 years of age.

Evidence that one dose of the HPV vaccine is enough has been building for some time, according to Julia Brotherton, Medical Director of Health at the Australian Center for the Prevention of Cervical Cancer.

“We have a limited supply of the vaccine and it is very expensive,” said Professor Brotherton, who is also a public health physician at the University of Melbourne.

But how do we know if one dose is enough protection, and should Australia – one of the first countries to roll out the HPV vaccine nationwide – make the switch from two injections to one?

Remember: What Does the HPV Vaccine Do?

There are two approved HPV vaccines in Australia. Currently, the most commonly used is Gardisil-9, available on the National Immunization Programme.

It protects against seven cancer-causing HPV types — not just cervical cancer, but anus and throat cancers — and two types that cause genital warts.

In 2018, it replaced an earlier version of Gardisil that was quadrivalent, meaning it was immunized against four types of HPV.

The other HPV vaccine, Cervarix, is bivalent. It only protects against HPV types 16 and 18.

Because HPV spreads through sexual contact, vaccines are best given to people before they are sexually active.

In Australia, they are usually administered to adolescents under 15, usually around 12 or 13 years old.

When the HPV vaccine was first introduced to non-immunocompromised adolescents under the National HPV Vaccination Program in 2007, a “completed course” was considered three doses over six months.

That changed in 2018after studies showed that two doses of the same vaccine, at least six months apart, worked just as well.

(People who begin HPV vaccination at age 15 or older, or who are immunocompromised, are still recommended to get three doses, if possible.)

And now it seems that one dose is enough.

How do we know that one dose is enough?

In about 15 years since the HPV vaccine was first rolled out, researchers have tracked cervical cancer rates in millions of girls and women around the world.

But recent studies have provided compelling evidence that just one dose of the vaccine is enough.

The first hint came from a vaccine trial in Costa Rica. It was designed to evaluate the efficacy of three doses, but a group of women in the study accidentally received only one or two doses.

“This was not meant to be,” Professor Brotherton said.

“People got pregnant or something else happened and they only got one dose.

The vaccine in the Costa Rica study was bivalent. Would the same be true for a quadrivalent vaccine?

An answer would come from India, where a large trial of a three-dose schedule was halted halfway through. This meant that many of the girls in the trial, aged between 10 and 18, received only one dose.

“But what we saw coming out of that cohort study was that the quadrivalent vaccine showed again” equivalent levels of protection in the girls who received only one dose as those who got two or three,” said Professor Brotherton.

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