Cervical Cancer Series 06 Does the HPV Vaccine Really Work?
Can the HPV vaccine really prevent cervical cancer?
Some people wonder whether the vaccine is effective enough because cervical cancer screening is still recommended after vaccination. Others may assume that receiving the HPV vaccine completely eliminates the possibility of developing cervical cancer.
The HPV vaccine cannot prevent every case of cervical cancer. However, by preventing infection with the high-risk HPV types responsible for most cervical cancers, it can substantially reduce the risk of precancerous lesions and cervical cancer.
This benefit is not limited to clinical trials. Data from national vaccination programs have shown reductions in vaccine-targeted HPV infections, cervical precancers, and even invasive cervical cancer.
This article explains how the vaccine works, when it provides the greatest benefit, and whether vaccination may still be worthwhile for adults or people who have tested positive for HPV.
How Does the HPV Vaccine Prevent Cancer?
The HPV vaccine is not a treatment that directly attacks or removes cancer cells. It is a preventive vaccine that helps interrupt the pathway to cancer by preventing new infections with HPV types associated with cervical cancer.
The vaccine contains virus-like particles designed to resemble the outer shell of HPV rather than the actual virus. These particles do not contain HPV genetic material, so the vaccine cannot cause HPV infection.
After vaccination, the immune system recognizes the virus-like particles and produces antibodies against them. If a person is later exposed to one of the HPV types covered by the vaccine, these antibodies help prevent the virus from infecting cells in the cervix and other areas.
Cervical cancer generally does not develop immediately after a person acquires a high-risk HPV infection. When the infection persists over time, it can cause changes in cervical cells. Some of these changes may progress through cervical intraepithelial neoplasia, or CIN, before becoming cancer.
By preventing new HPV infections, the vaccine reduces the chance of persistent infection and, in turn, lowers the risk of precancerous lesions and cervical cancer.
The process can be summarized as follows:
HPV vaccination → antibody production → prevention of new HPV infections → fewer persistent infections → lower risk of precancerous lesions and cervical cancer
However, because the HPV vaccine is preventive, it cannot eliminate an existing HPV infection or reverse abnormal cell changes that have already developed.
Which HPV Types Can the Vaccine Prevent?
There are many types of HPV, and not all of them cause cancer.
HPV types 16 and 18 are the most important high-risk types and are associated with approximately 70% of cervical cancers worldwide. HPV types 31, 33, 45, 52, and 58 are also major high-risk types associated with cervical cancer.
The 9-valent HPV vaccine, which is widely used today, targets nine HPV types:
HPV types 16, 18, 31, 33, 45, 52, and 58: High-risk types associated with cervical cancer and other HPV-related cancers
HPV types 6 and 11: Low-risk types responsible for most cases of genital warts
The 9-valent vaccine provides broad protection against the major high-risk HPV types associated with cervical cancer. However, it does not protect against every HPV type that can potentially cause cancer.
The vaccine can therefore substantially reduce the risk of cervical cancer, but it cannot eliminate that risk entirely.
Has Cervical Cancer Actually Decreased?
The effectiveness of HPV vaccination was first demonstrated in clinical trials showing that it could prevent HPV infections and cervical precancers. As vaccination programs became more widespread, the benefits also began to appear in real-world population data.
In the United States, compared with the period before HPV vaccination was introduced, infections with the HPV types targeted by the original quadrivalent vaccine declined by 88% among females aged 14 to 19 and by 81% among females aged 20 to 24. Among vaccinated women, the proportion of cervical precancers caused by vaccine-targeted HPV types also decreased.
Determining whether vaccination reduces cervical cancer itself takes much longer than measuring changes in HPV infection or precancerous lesions. This is because cervical cancer typically develops over many years after an HPV infection occurs.
As more time has passed since national vaccination programs were introduced, studies have begun to document reductions in cervical cancer as well.
An analysis of England’s national HPV vaccination program found that cervical cancer incidence was 87% lower among those who had been offered vaccination at ages 12 to 13 than in the reference group from before the vaccination program was introduced. The incidence of CIN3, a high-grade precancerous lesion, was 97% lower.
The reduction became smaller as the age at which vaccination was offered increased. This supports the importance of vaccination before a person is likely to be exposed to HPV.
A nationwide registry study from Sweden also found an association between HPV vaccination and a lower risk of invasive cervical cancer. The reduction was greater among those who had been vaccinated before age 17.
These findings show that the benefits of HPV vaccination extend beyond changes in HPV infection rates or screening results. Population studies from countries with established vaccination programs have documented reductions in both cervical precancers and invasive cervical cancer.
However, these figures come from studies comparing populations at the national level. They do not guarantee that every vaccinated individual’s risk will fall by exactly the same percentage, nor do they mean that cervical cancer can never occur after vaccination.
Why Is Vaccination More Effective at a Younger Age?
The HPV vaccine works best against HPV types a person has not yet acquired. It is therefore important to vaccinate before there is a likelihood of exposure to HPV.
Vaccination is recommended during adolescence so that protection can develop before potential exposure to the virus—not as a judgment about whether a young person is sexually active.
The U.S. Centers for Disease Control and Prevention, or CDC, provides the following recommendations:
Routine HPV vaccination is recommended at ages 11 to 12.
Vaccination can begin as early as age 9.
Catch-up vaccination is recommended through age 26 for people who were not adequately vaccinated at the recommended age.
Most people who begin the series before their 15th birthday receive two doses.
People who begin the series at age 15 or older generally receive three doses.
A three-dose series is also recommended for immunocompromised people, including those with HIV, from ages 9 through 26.
These are U.S. recommendations. The recommended ages and number of doses may vary depending on national vaccination policies, previous vaccination history, and immune status. It is helpful to review your vaccination record and discuss the appropriate schedule with a healthcare professional.
Can the Vaccine Still Work If Given During Adulthood?
The HPV vaccine provides the greatest preventive benefit when given during adolescence, but some adults may still benefit from vaccination.
Adults are more likely than adolescents to have already been exposed to one or more HPV types. However, having previous sexual experience or receiving a positive HPV test result does not mean that a person has been infected with every HPV type covered by the vaccine.
The vaccine may still help prevent new infections caused by vaccine-targeted HPV types to which the person has not yet been exposed.
The CDC recommends catch-up vaccination through age 26 for people who have not been adequately vaccinated. HPV vaccination is not routinely recommended for every adult aged 27 to 45. Instead, some unvaccinated or incompletely vaccinated adults in this age group may decide whether to receive the vaccine after discussing its potential benefits with a healthcare professional.
Factors that may be considered include:
Whether the person has previously received HPV vaccination and completed the recommended series
The possibility of future exposure to new HPV infections
The possibility of having a new sexual partner in the future
Individual health conditions that should be discussed with a healthcare professional
People in a long-term, mutually monogamous relationship may have a relatively low likelihood of acquiring a new HPV infection. By contrast, having a new sexual partner in the future can create a new opportunity for HPV exposure.
Adult vaccination should therefore not be dismissed as “too late to be useful,” nor should it be assumed to provide everyone with the same benefit expected from vaccination during adolescence. The potential benefit depends on the individual’s circumstances and should be discussed with a healthcare professional.
Is the Vaccine Useless After an HPV-Positive Result?
An HPV-positive test result does not necessarily mean that HPV vaccination has no value.
An HPV-positive result means that at least one of the high-risk HPV types included in the test was detected. Depending on the test, specific HPV types may be identified separately, while other tests report several high-risk types together as a single positive result.
In either case, testing positive for HPV does not mean that a person has already acquired every HPV type covered by the vaccine. The vaccine may still provide protection against other targeted types that the person has not acquired.
However, the role and limitations of vaccination must be clearly distinguished.
The HPV vaccine cannot eliminate an existing HPV infection. It does not make the infection clear more quickly, nor does it treat cervical intraepithelial neoplasia or abnormal cells that have already developed.
A person who receives an HPV-positive result or an abnormal Pap test must therefore continue the follow-up testing and medical care recommended for the existing infection or cell changes, even if they receive the vaccine.
Vaccination to prevent future infections with HPV types not yet acquired and medical care for a currently detected HPV infection are two separate issues.
Should Men Receive the HPV Vaccine?
HPV is not a virus that affects only women or causes only cervical cancer.
HPV infection in men can also be associated with:
Anal cancer
Penile cancer
Oropharyngeal cancer
Genital warts
The most important reason for men to receive the HPV vaccine is to protect themselves against HPV-related cancers and other diseases. Increasing vaccination coverage may also help reduce the spread of vaccine-targeted HPV types within the population.
Vaccination in men should therefore not be viewed solely as a way to prevent transmission to women. Men are themselves directly at risk of HPV-related diseases and can benefit from protection.
Vaccinating both males and females at the recommended ages helps protect individual health and reduce the overall burden of HPV-related disease.
How Long Does Protection Last?
Some people may worry that the protection provided by HPV vaccination will disappear over time.
Follow-up studies have shown that HPV vaccine protection remains strong for more than a decade, with no evidence that protection decreases over time. Routine booster doses are not currently recommended.
However, this does not mean that lifelong protection has been conclusively established. Research into the long-term duration of protection is continuing.
Based on current evidence, HPV vaccine protection remains strong for many years, and no clear decline has been identified.
Do You Still Need Cervical Cancer Screening After HPV Vaccination?
People who are eligible for cervical cancer screening should continue screening after HPV vaccination.
The vaccine protects against the major high-risk HPV types responsible for cervical cancer, but it does not cover every high-risk type. A person may also have been exposed to a particular HPV type before receiving the vaccine.
HPV vaccination and cervical cancer screening serve different purposes:
HPV vaccination: Prevents new infections with the HPV types covered by the vaccine.
Cervical cancer screening: Detects high-risk HPV infections or cervical cell changes that have already developed.
Vaccination and screening are therefore not substitutes for one another. Receiving the vaccine at the appropriate time and continuing regular screening according to age and national guidelines are both important.
Key Takeaways
The HPV vaccine prevents new infections with the high-risk HPV types responsible for most cervical cancers. Real-world vaccination data have documented reductions in vaccine-targeted HPV infections, cervical precancers, and invasive cervical cancer.
Vaccination provides the greatest benefit when given before HPV exposure. However, some adults and people who have previously tested positive for HPV may still benefit from protection against vaccine-targeted types they have not yet acquired.
The HPV vaccine does not treat an existing HPV infection, CIN, or abnormal cervical cells. It also does not prevent every high-risk HPV type, so people who are eligible for cervical cancer screening should continue screening after vaccination.
The HPV vaccine cannot eliminate every possibility of cervical cancer, but it is an effective cancer prevention tool that can substantially reduce the risk. Timely vaccination and regular cervical cancer screening remain the most important complementary strategies.
References
Centers for Disease Control and Prevention. HPV Vaccine Recommendations.
https://www.cdc.gov/hpv/hcp/vaccination-considerations/index.htmlCenters for Disease Control and Prevention. HPV Vaccine Safety and Effectiveness Data.
https://www.cdc.gov/hpv/hcp/vaccination-considerations/safety-and-effectiveness-data.htmlNational Cancer Institute. Human Papillomavirus (HPV) Vaccines.
https://www.cancer.gov/about-cancer/causes-prevention/risk/infectious-agents/hpv-vaccine-fact-sheetNational Cancer Institute. Recombinant Human Papillomavirus Nonavalent Vaccine.
https://www.cancer.gov/about-cancer/treatment/drugs/recombinant-hpv-nonavalent-vaccineFalcaro M, Castañon A, Ndlela B, et al. The effects of the national HPV vaccination programme in England, UK, on cervical cancer and grade 3 cervical intraepithelial neoplasia incidence: a register-based observational study. The Lancet. 2021;398(10316):2084–2092.
https://pubmed.ncbi.nlm.nih.gov/34741816/Lei J, Ploner A, Elfström KM, et al. HPV Vaccination and the Risk of Invasive Cervical Cancer. The New England Journal of Medicine. 2020;383(14):1340–1348.
https://pubmed.ncbi.nlm.nih.gov/32997908/Rosenblum HG, Lewis RM, Gargano JW, et al. Declines in Prevalence of Human Papillomavirus Vaccine-Type Infection Among Females after Introduction of Vaccine—United States, 2003–2018. Morbidity and Mortality Weekly Report. 2021;70(12):415–420.
https://www.cdc.gov/mmwr/volumes/70/wr/mm7012a2.htmWorld Health Organization. Human Papillomavirus and Cancer.
https://www.who.int/news-room/fact-sheets/detail/human-papilloma-virus-and-cancer
Comments
Post a Comment