Human
Papillomavirus Vaccines: Questions and Answers
What are human papillomaviruses?
Human papillomaviruses
(HPVs) are a group of more than 100 viruses. They are called papillomaviruses
because certain types may cause warts, or papillomas, which are
benign (noncancerous) tumors. The HPVs that cause the common warts
that grow on hands and feet are different from those that cause
growths in the throat or genital area. Some types of HPV are associated
with certain types of cancer. These are called "high-risk"
oncogenic or carcinogenic HPVs.
Of the more than 100
types of HPV, over 30 types can be passed from one person to another
through sexual contact. Although HPVs are usually transmitted sexually,
doctors cannot say for certain when infection occurred. About 6
million new genital HPV infections occur each year in the United
States . Most HPV infections occur without any symptoms and go away
without any treatment over the course of a few years. However, HPV
infection sometimes persists for many years, with or without causing
detectable cell abnormalities.
Do HPV
infections cause cancer?
Infection with
certain types of HPV is the major cause of cervical cancer. Almost
all women will have HPV infections at some point, but very few will
develop cervical cancer. The immune system of most women will usually
suppress or eliminate HPV. Only HPV infections that are persistent
(do not go away over many years) can lead to cervical cancer. In
2006, an estimated 10,000 women in the United States will be diagnosed
with this type of cancer and nearly 4,000 will die from it. Cervical
cancer strikes nearly half a million women each year worldwide,
claiming more than a quarter of a million lives. Studies also suggest
that HPVs may play a role in cancers of the anus, vulva, vagina,
and some cancers of the oropharynx (the middle part of the throat
that includes the soft palate, the base of the tongue, and the tonsils).
Data from several studies also suggest that infection with HPV is
a risk factor for cancer of the penis.
Can
HPV infection be prevented?
The surest way to eliminate
risk for genital HPV infection is to refrain from any genital contact
with another individual.
For those who choose
to be sexually active, a long-term, mutually monogamous relationship
with an uninfected partner is the strategy most likely to prevent
genital HPV infection. However, it is difficult to determine whether
a partner who has been sexually active in the past is currently
infected.
It is not known how much
protection condoms provide against HPV infection, because areas
not covered by a condom can be infected by the virus. Although the
effect of condoms in preventing HPV infection is unknown, condom
use has been associated with a lower rate of cervical cancer, an
HPV-associated disease.
In 2006, the U.S. Food
and Drug Administration (FDA) approved a vaccine that is highly
effective in preventing persistent infection with HPV types 16 and
18, two "high-risk" HPVs that cause most (70 percent)
cervical cancers, and types 6 and 11, which cause virtually all
(90 percent) genital warts (3).
What
preventive HPV vaccines are available?
The Gardasil vaccine,
which is produced by Merck & Co., Inc. (Merck), is called a
quadrivalent vaccine because it protects against four HPV types:
6, 11, 16, and 18. Gardasil is given through a series of three injections
into muscle tissue over a 6-month period.
Another promising vaccine,
Cervarix™, is produced and is being tested by GlaxoSmithKline
(GSK), but is not yet approved by the FDA. This vaccine is called
a bivalent vaccine because it targets two HPV types: 16 and 18.
This vaccine is also given in three doses over a 6-month period.
Early findings have shown that Cervarix also protects against persistent
infection with HPV 16 and 18.
Both Gardasil and Cervarix
are based on technology developed in part by National Cancer Institute
(NCI) scientists. NCI, a part of the National Institutes of Health,
licensed the technology to two pharmaceutical companies—Merck
and GSK—to develop HPV vaccines for widespread distribution.
Neither of these
HPV vaccines has been proven to provide complete protection against
persistent infection with other HPV types, including other types
that cause cervical cancer. Therefore, about 30 percent of cervical
cancers and 10 percent of genital warts will not be prevented by
these vaccines. In addition, the vaccines do not prevent other sexually
transmitted diseases, nor do they treat HPV infection or cervical
cancer.
Because the
vaccines will not protect against all infections that cause cervical
cancer, it is important for vaccinated women to continue to undergo
cervical cancer screening as is recommended for women who have not
been vaccinated.
How
do HPV vaccines work?
The HPV vaccines work
like other immunizations that guard against viral infection. The
investigators hypothesized that the HPVs unique surface components
might create an antibody response that is capable of protecting
the body against infection, and these components could be used to
form the basis of a vaccine. These surface components can interact
with one another to form virus-like particles (VLP) that are noninfectious
and stimulate the immune system to produce antibodies that can prevent
the complete papillomavirus from infecting cells. They are thought
to protect primarily by causing the production of antibodies that
prevent infection and the development of those cervical cell changes
seen on Pap tests that may lead to cancer (4). Although these vaccines
can help prevent HPV infection, it is not known if they can help
eliminate existing cervical cell changes due to HPVs.
How
effective are the HPV vaccines?
These two vaccines
are highly effective in preventing infection with the types of HPV
that they target. The vaccine approved by the FDA (Gardasil) prevented
nearly 100 percent of the precancerous cervical cell changes caused
by the types of HPV targeted by the vaccine for up to 4 years after
vaccination.
Why
are these vaccines important?
Widespread vaccination
has the potential to reduce cervical cancer deaths around the world
by as much as two-thirds, if all women were to take the vaccine
and if protection turns out to be long-term. In addition, the vaccines
can reduce the need for medical care, biopsies, and invasive procedures
associated with the follow-up from abnormal Pap tests, thus helping
reduce health care costs and anxieties related to abnormal Pap tests
and follow-up procedures (2).
How
safe are the HPV vaccines?
Before any vaccine
is licensed, the FDA must determine that it is both safe and effective.
Both vaccines have been tested in thousands of people in the United
States and many other countries. Thus far, no serious side effects
have been noted. The most common problem has been brief soreness
at the site of injection and other local injection site symptoms
commonly experienced with other childhood vaccines.
How
long do the vaccines protect against infection?
The duration
of immunity is not yet known. Research is being conducted to find
out how long protection will last. Studies thus far have shown that
Gardasil can provide protection against HPV 16 for 4 years. Studies
with the bivalent vaccine produced by GSK showed protection from
infection with both HPV 16 and 18 for more than 4 years.
Will
booster vaccinations be needed?
Studies are
under way to determine whether a booster vaccination is necessary.
Who
should get the HPV vaccines?
The vaccines
are proven to be effective only if given before infection with HPV,
which would be before an individual is sexually active. The FDA-licensing
decision includes information about the age and sex for recipients
of the vaccine. For Gardasil, the age range is 9 to 26 years.
After a vaccine
is licensed by the FDA, the Advisory Committee on Immunization Practices
(ACIP) makes additional recommendations to the Secretary of the
U.S. Department of Health and Human Services (DHHS) and the Director
of the Centers for Disease Control and Prevention (CDC) on who should
receive it, at what age, how often, the appropriate dose, and situations
in which it should not be administered. ACIP is made up of 15 experts
in fields associated with immunization. ACIP provides advice on
the most effective ways to use vaccines to prevent diseases. ACIP
recommendations are not binding but are usually followed by health
care professionals and often influence insurance reimbursement.
More information about ACIP can be found on the CDC Web site at
http://www.cdc.gov/nip/ACIP/default.htm on the Internet.
In addition,
states can decide whether or not to require vaccinations prior to
enrollment in schools or child care. Each state makes this decision
individually. Information about specific state vaccine decisions
is available from the National Network for Immunization Information
(NNii) Web site at http://www.immunizationinfo.org/vaccineInfo/index.cfm#state
on the Internet.
Should
the vaccine be given to people who are already infected with HPV?
The preventive
vaccines currently under study do not treat infections, although
they have been found to be generally safe when given to women who
are already infected with HPV. It is not feasible to pre-screen
all women to see who has been exposed to the HPV types in the vaccines.
At present, there is no generally available test to tell whether
an individual has been exposed to HPV. The currently approved test
only shows whether a woman has a current HPV infection and identifies
the HPV type. It does not provide information on past infections.
The decision to vaccinate or not, based on likelihood of prior exposure
to these HPV types, is being discussed by ACIP and other advisory
groups.
Should
women who already have cervical cell changes get the vaccine?
The vaccine
appears to be safe in women who have cervical abnormalities, but
it is not known if the vaccine would help clear the abnormality.
Women should talk with their health care providers about treatment
for abnormal cervical cell changes.
Do women
who have been vaccinated still need to have Pap tests?
Because the
vaccine does not protect against all HPV types, Pap tests to screen
for cervical cancer continue to be essential to detect cervical
cancers and precancerous changes. In addition, Pap tests are critically
important for women who have not been vaccinated or are already
infected with HPV.
How
much will the vaccine cost, and will insurance pay for it?
The cost of
the vaccine is not known at this time. However, a Merck company
cost-effectiveness analysis assumed a cost of $300 to $500. Individual
or group insurance plans are subject to state laws. These laws generally
establish coverage based on recommendations from the ACIP. Medicaid
coverage is in accordance with the ACIP standard and immunizations
are a mandatory service under Medicaid for eligible individuals
under age 21. Medicaid also includes the Vaccines for Children Program
(VFC). This program provides immunization services for children
18 and under who are Medicaid eligible, uninsured, underinsured,
and receiving immunizations through a Federally Qualified Health
Center or Rural Health Clinic, or are Native American or Alaska
Native.
What
research is being done with HPV?
Researchers at NCI and
elsewhere are studying how HPVs cause precancerous changes in normal
cells and how these changes can be prevented. For example, a study
is under way to determine if a vaccine can prevent infection with
HPV types other than those targeted by Gardasil and Cervarix and
to better understand the way the vaccines work (see Question 5)
and factors that predict duration of protection. NCI is conducting
a large clinical trial of the HPV vaccine manufactured by GSK in
Costa Rica , where cervical cancer rates are high. This study is
designed to obtain information about the vaccine’s long-term
safety and the extent and duration of protection. NCI is also collaborating
with other researchers on therapeutic HPV vaccines that would prevent
the development of cancer among women previously exposed to HPV.
For use in the general population, the ideal vaccine strategy would
combine a preventive and therapeutic vaccine.
Laboratory research
has indicated that HPVs produce proteins known as E5, E6, and E7.
These proteins interfere with the cell functions that normally prevent
excessive growth. For example, HPV E6 interferes with the human
protein p53, which is expressed by the p53 gene in all people and
acts to keep tumors from growing. This research is being used to
develop ways to interrupt the process by which HPV infection can
lead to the growth of abnormal cells.
Researchers
at the NCI and elsewhere are also studying what people know and
understand about HPV and cervical cancer, the best way to communicate
to the public about the latest research results, and how doctors
are talking with their patients about HPV. This research will help
to ensure that the public receives accurate information about HPV
that is easily understood, and will facilitate access to appropriate
tests for those who need them.
Source
National Cancer Institute
http://www.cancer.gov/
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