First, let me provide a bit of background on the disease. Genital human papillomavirus (HPV) is the most common sexually transmitted infection (STI) in the USA. There are more than 40 HPV sub-types that can infect the genital areas of males and females. These same HPV types can also infect the mouth, anus and throat. They are transmitted from personal contact during vaginal, anal or oral sex.

Some HPV subtypes, such as HPV-6 and HPV-11, can cause warts around the genitals or anus, but have low (but not 0) risk of causing cancers. However, the higher risk subtypes, such as HPV 16 and 18, not only cause approximately 70% of cervical cancers, but they cause most HPV-induced anal (95% linked to HPV), vulvar (50% linked), vaginal (65% linked), oropharyngeal (60% linked) and penile (35% linked) cancers. HPV is estimated to be the cause of nearly 5% of all new cancers across the world.

Currently in the United States, the Advisory Committee on Immunization Practices (ACIP) recommends that preteen girls and boys aged 11 or 12 are vaccinated against HPV. The immunization is also recommended for teenage girls and young women up to the age of 26 who did not receive it when they were younger, and teenage boys and young men up to the age of 21.

One of the concerns (usually promoted by antivaccine groups, but usually dismissed by real researchers with real experience with vaccines) is that it is unknown whether the immunization's effects last longer than a few years. Because Gardasil was only approved in 2006 (although there are, of course, patients who received it during clinical trials during the prior years), data can only be assessed for the past few years, unlike other vaccines that have been available for decades. Thus, we can expect that nearly every year, new data will be published to provide evidence that the vaccination's effectiveness lasts one additional year.

And a recent study, published in Pediatrics, provides evidence that the effectiveness, measured by the immunity provided by the HPV vaccine, lasted at least 8 years. The study followed 1781 children, ages 9-15, for 8 years following vaccination with the HPV quadrivalent vaccine (about ⅔ of the group) or a placebo (about ⅓). At month 30, the placebo group received the vaccine (see Note 3).

The researchers determined the effectiveness of the vaccine by testing the participants' blood for anti-HPV seropositivity (that is, indication of antibodies to HPV in the blood). The results of the study provide more powerful evidence of the effectiveness of the vaccine:



Vaccination-induced anti-HPV response was clinically detectable through month 96 (or 8 years).

Among the 429 children who received the vaccine at an average age of 12, none developed any of the four subtypes of HPV disease or persistent infection of ≥12 months’ duration.

Acquisition of new sexual partners (among those ≥16 years) was ~1 per year, further indication that the HPV vaccine did not encourage increased sexual activity.

The patients who received the placebo, but subsequently at 30 months received the regular HPV vaccine, had a similar baseline rate of seropositivity to all of the 4 HPV types as those vaccinated at day 1.

No new significant serious adverse events were observed for 8 years postvaccination in both genders.

The HPV4 vaccine administered to preadolescents and adolescents demonstrated durability in clinically effective protection and sustained antibody titers over 8 years. No new significant serious adverse events were observed for 8 years after vaccination in both genders. These long-term follow-up data, along with other extensive post-approval safety surveillance data, should help to encourage practitioners and reinforce national recommendations for HPV vaccination of all preadolescents and young adolescents.

The study authors concluded that:I don't know how to say this in a new and different way. Gardasil is safe, researchers are not finding any substantial adverse events in large studies. Gardasil is effect, it prevents HPV infection which can lead to cancer. Gardasil simply saves lives.

Notes:

(1) An HPV bivalent vaccine, known as Cervarix, is used in some countries, but only provides protection again two of the subtypes most associated with cervical cancer.

(2) There's a whole mythology surrounding the number 47 in the Star Trek canon. My use of it is completely random.

(3) One of the criticisms made by antivaccine groups about vaccine trials is that they rarely, if ever, contain a placebo group. The reason for this clinical trial design is that it would be unethical to put the placebo group at risk of a deadly disease. Some infectious diseases, like whooping cough, can be spread so easily that the placebo group could get sick (and some die) without the vaccine. In this case, because of the early age of the participants, the risk of contracting HPV in the placebo group is negligible. In addition, the placebo group did eventually receive the vaccine at 30 months, and the results showed that they were equally protected.

Key citations:

