Rates for two types of HPV viruses linked to cervical cancer have plummeted since the vaccine was rolled out, a new study finds.
Researchers at the Centers for Disease Control and Prevention (CDC) say that cases of women positive for HPV types 16 and 18 – responsible for about 70 percent of cervical cancers worldwide – fell by more than 30 percent.
Cases declined even among unvaccinated women, which scientists say is likely due to ‘herd immunity’, meaning enough people were vaccinated against the disease so that they were immune to it and unable to spread it.
The team says its encouraged by the results and said it expects to see even further declines as more teenage girls, young women – and even boys – decide to get vaccinated.
A new study has found that cases of women positive for HPV types 16 and 18 – responsible for about 70 percent of cervical cancers worldwide – fell by more than 30 percent from 2008 to 2014 (file image)
HPV, short for Human papillomavirus, is the most common STI in the US, affecting around 79 million people. It has been linked to numerous cancers – including prostate, throat, head and neck, rectum and cervical cancer.
Since the HPV vaccine was introduced in 2006, 79 countries and territories have implemented a publicly funded national HPV vaccination program.
In the US, the vaccine is offered in two or three doses over the course of six months to girls who are between 11 and 12, with a catch-up series recommended no later than age 26.
In the UK, all girls between ages 12 and 18 are offered free vaccination against HPV over six to 12 months, but until recently it wasn’t offered to boys.
In July of last year, government officials finally announced that the National Health Service will inoculate 12- and 13-year-old boys as well after a prevalence of head and neck cancers was seen in men.
Ireland followed suit and also announced that the HPV vaccine will be given to boys in 2019.
According to the CDC, each year about 19,000 cancers caused by HPV occur in women in the US, with cervical cancer being the most common.
And about 8,000 cancers caused by HPV occur each year in men in the US and oropharyngeal (throat) cancers are the most common.
‘Almost all sexually active individuals will get HPV at some point in their lifetime, but most HPV infections go away on their own without any treatment,’ said lead author Dr Nancy McClung, an epidemic intelligence service officer at the CDC.
‘If an HPV infection does not go away, it can cause cell changes that, over time, develop into a lesion on the cervix called a cervical precancer.
‘Cervical precancers allow us to observe the impact of HPV vaccination earlier than cervical cancer, which can take decades to develop.’
For the study, the team looked at data from the CDC’s HPV Vaccine Impact Monitoring Project.
The surveillance project looks at the HPV vaccine’s impact on types of the virus that are linked to cervical cancer and precancers.
Researchers analyzed more than 10,000 specimens collected from women between ages 18 and 39 from 2008 to 2014.
The women had been diagnosed with either cervical intraepithelial neoplasia grades 2-3 or adenocarcinoma in situ (CIN2+).
Both are conditions in which abnormal cells are found in the cervix due to an HPV infection that is not cleared by the immune system.
The team found that the number of CIN2+ cases dropped 21 percent from more than 2,300 in 2008 to less than 1,900 in 2014.
The number of cases due to HPV 16/18 fell by 33 percent from 1,235 in 2008 to 819 cases in 2014.
The proportion of CIN2+ cases that were HPV 16/18-positive for vaccinated women plummeted from around 55 percent to about 33 percent.
In unvaccinated women, it dropped from 51 percent to around 47 percent. For women whose vaccination status was unknown, the proportion also declined from nearly 54 percent to about 46 percent.
Dr McClung says one reason vaccinated women were positive for HPV 16/18 is because they were infected before receiving the jab in their early 20s, likely after they began having sex.
She also noted that the number of unvaccinated women with the virus dropped due to ‘herd protection’, also known as ‘herd immunity’.
This occurs when the vast majority of a community – between 80 and 95 percent – becomes immune so that, if a disease is introduced, it is unable to spread.
It helps ensure those who are unable to be vaccinated are protected.
Results also showed that every age group saw notable declines in cases of CIN2+ that were HPV 16/18-positive, except among women between ages 35 and 39.
However, Dr McClung said this is likely because they were never vaccinated because they were too old to receive.
She added said the results are evidence that recent efforts to encourage teenagers and young adults to be inoculated is working and that it needs to continue.
‘This is clear evidence that the HPV vaccine is working to prevent cervical disease in young women in the United States,’ Dr McClung said.
‘In the coming years, we should see even greater impact as more women are vaccinated during early adolescence and before exposure to HPV.’