Overall impact on cancer rates will take 25-plus years to see
Johns Hopkins University Bloomberg School of Public Health
Vaccinations against human papillomavirus (HPV), a major cause of throat and back of mouth cancers, are expected to yield significant reductions in the rates of these cancers in the U.S., but will not do so until after 2045, according to a new modeling study from researchers at the Johns Hopkins Bloomberg School of Public Health.
HPV is the most common sexually transmitted infectious virus worldwide. HPV infections are often silent, and while most infections clear, some are chronic and can trigger cancers including mouth and throat (oropharyngeal), and cervical cancer because they disrupt DNA and inhibit tumor-suppressor proteins in the cells they infect.
Although there is no cure for existing HPV
infections, new infections are preventable with vaccines, the first of which
entered use in the U.S. in 2006.
In the new study, the Bloomberg School researchers analyzed national databases on oropharyngeal cancer cases and HPV vaccinations, and projected the impact of HPV vaccination on the rates of these cancers in different age groups.
They
estimated that the oropharyngeal cancer rate would nearly halve between 2018
and 2045 among people ages 36-45. However, they also projected that the rate in
the overall population would stay about the same from 2018-2045, due to
still-rising rates of these cancers in older people, where most of these
cancers occur.
 |
| Left-right: Reps. Justin Price, Blake "Flip" Filippi and Sen. Elaine Morgan. Flip and Morgan represent Charlestown. Price represents neighboring CHARIHO towns. All three oppose a Rhode Island mandate for vaccinations against HPV cancers in schools. (Photo by Steve Ahlquist) |
The study appears online September 2 in JAMA Oncology.
"We
estimate that most of the oropharyngeal cancers from 2018 to 2045 will occur
among people who are 55 years and older and have not been vaccinated,"
says study lead author Yuehan Zhang, a PhD candidate in the research group of
Gypsyamber D'Souza, PhD, professor in the Department of Epidemiology at the
Bloomberg School.
"HPV
vaccination is going to work to prevent oropharyngeal cancers, but it will take
time to see that impact, because these cancers mostly occur in middle
age," D'Souza says.
Oropharyngeal
cancer is the most common HPV-related cancer, and according to the Oral Cancer
Foundation there are more than 50,000 new cases of it in the U.S. each year.
Alcohol and tobacco use also are risk factors, but are seen as increasingly
less important than HPV.
Vaccination
is a powerful medical weapon against this family of viruses, but has one major
shortcoming: It can prevent, but not treat. In other words, it does not work
against established HPV infections or against cells that have been transformed
by HPV and are on their way to forming tumors. Thus it is recommended chiefly
for the young who are not yet exposed to sexually transmitted HPV. (Most people
who were already adults when HPV vaccination became available have never been
vaccinated, and thus remain at risk for these cancers.)
For
the study, the researchers estimated current and future HPV vaccination rates
using data from surveys conducted by the U.S. Centers for Disease Control and
Prevention, and projected oropharyngeal cancer rates based on past and current
incidence data from the National Cancer Institute.
They
estimated that the rates of vaccination by 2045, for different age groups --
given the emphasis on vaccinating the young -- will amount to about 72 percent
of people ages 36-45, 37 percent of those ages 46-55, 9 percent of those ages
56-69, and 0 percent of people ages 70-83 being vaccinated.
These
projections show continuing high oropharyngeal cancer rates in older, mostly
unvaccinated groups, and almost no change in the overall U.S. rate of these
cancers -- 14.3 per 100,000 assuming no vaccination; and 13.8 per 100,000, with
vaccination, in 2045.
However,
they foresaw the rates of new oropharyngeal cancers would fall substantially in
the relatively well vaccinated 36-45 and 46-55 age groups during the 2018-2045
period: from 1.4 to 0.8 per 100,000; and from 8.7 to 7.2 per 100,000,
respectively.
The
results suggest, though, that by 2045 HPV vaccination will have begun to make a
significant impact. "Our projections suggest that by around 2033, nearly
100 cases of oropharyngeal cancer will be prevented each year, but by 2045 that
figure will have increased by about ten times," Zhang says.
Funding
was provided by the National Institute of Dental and Craniofacial Research
(R35DE026631).
