Researchers have attributed a substantial drop in human papillomavirus (HPV) infections to the HPV vaccine. Now, they are waiting to see if it will have the same impact on the rates of cervical cancer.
Just over a decade ago, healthcare professionals introduced a new vaccination that aimed to prevent recurring infections of certain types of HPV. These infections can, if a person does not receive treatment, lead to cervical cancer.
According to the National Institutes of Health (NIH), this form of cancer is the third most common among women.
The invention of the Pap smear significantly reduced deaths from cervical cancer in the United States, but the condition is still responsible for around 300,000 deaths worldwide every year.
Researchers and healthcare professionals hope that the HPV vaccine will significantly reduce the prevalence of cervical cancer. But it is still too early to determine its potential effectiveness.
However, researchers are able to measure the effects of vaccination programs on the prevalence of HPV infection. They can also measure the prevalence of precancerous lesions caused by the virus before and after the implementation of the vaccine.
These lesions can appear in several places, including the cervix, mouth, vagina, anus, and penis.
How the vaccine works
HPV, on the whole, has been tricky to combat. There are more than 100 known strains of the virus. Around 40 of these can be sexually transmitted, and approximately 15 have the ability to cause cancer.
The existing vaccine targets the two strains responsible for 70% of cervical cancer cases, HPV-16 and HPV-18, along with five other high-risk strains. One version of the vaccine also protects against strains that cause 90% of genital warts cases.
Doctors recommend the vaccine for children ages 11–12. For those who have yet to receive the vaccine, doctors tend to administer it in women up to age 26 and in men up to age 21, though some men may benefit from receiving it up to age 26.
To see how effective these vaccines have been, a group of researchers from the Centre de Recherche du CHU de Québec—Université Laval, in Canada, have analyzed 65 studies from 14 countries that have an HPV vaccination program. Their findings appear in The Lancet.
To be eligible, studies had to have been published between 2014 and 2018. They also needed to compare pre- and post-vaccination prevalence of at least one of the following: HPV infections, anogenital warts, or precancerous cervical lesions.
The resulting data came from 60 million people. The researchers carried out an analysis to find the potential impact of the vaccine 1–4 years and 5–8 years after vaccination. They broadened this time frame to 9 years when studying the effect on lesions.
The team then compared data from countries with a vaccination coverage of at least 50% and those with lesser coverage, as well as data from countries that vaccinated at multiple ages and those that vaccinated within only one age range.
A significant reduction
The researchers found that for girls ages 13–19, HPV infections had reduced by 83%. The reduction was slightly less significant, 66%, among women ages 20–24.
The team noticed a similar pattern for both anogenital warts and precancerous cervical lesions. For the former, the analysis revealed a reduction of 67% among girls ages 15–19 and 54% among women ages 20–24.
Furthermore, the study recorded a 51% reduction in legions among girls ages 15–19, along with a 31% drop among women ages 20–24.
There also appears to be a benefit to males. Cases of anogenital warts in 15- to 19-year-old boys decreased by 48% and 20- to 24-year-old men saw a reduction of 32%.
When it came to comparing results from high- and low-coverage countries, the researchers concluded that high-coverage countries saw the most benefits. This was also the case for countries that vaccinated females in more than one age group.
Although these figures are impressive, not every country is experiencing the same drop in numbers. Some do not vaccinate at all, while others have lower rates due to unsubstantiated fears that the vaccine causes illnesses.
But, as lead author Mélanie Drolet, Ph.D., explains, “These reductions are a first sign that vaccination could eventually lead to the elimination of cervical cancer as a public health problem.”
We are now trying to determine when elimination could be achieved and which vaccination and screening programs could help us achieve it faster.
Mélanie Drolet, Ph.D.
It may still be necessary to develop a vaccine that works against a wider range of HPV strains. In the meantime, facilitating global implementation of the current HPV vaccine is likely to be the next vital step.