September 18, 2020

Cervical Cancer : The Vaccine that protects

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Dr Lynn Dawber is a South African national joining the International Medical Group from New Zealand where she has been practicing for a number of years.

Human papilloma virus (HPV) and cervical cancer

The recognition of the role of HPV in the cause of cervical cancer led to the development of preventative vaccines.

There are over 100 types of HPV and around 30–40 of these are known to infect the genital tract – of these around 15 are known to be cancer causing. HPV is also a significant contributor to other cancers and is estimated to contribute in up to 85% of anal cancers, 50% of vaginal, and penile cancers, 20% of mouth and throat cancers.

Vaccines against HPV

The vaccines available target HPV type 16 and 18 viruses. Types 16 and 18 combined are implicated in approximately 70% of cervical cancer internationally.

GardasilTM contain HPV types 6, 11, 16 and 18. Type 6 and 11 are not implicated in cervical cancer, but are responsible for over 90% of genital warts, and contribute to low grade cervical abnormalities. Cervarix only contains type 16 and 18.

Clinical trials show that both vaccines are effective and have excellent safety profiles.

Efficacy of vaccines

Trials have shown almost 100% efficacy against persistent HPV infection 16 and 18.

Duration of immunity

HPV infection peaks at approximately 20 years of age. This leads to peak incidence of abnormal cervical changes in the 25–30 year old age group, and cervical cancer from mid-life. Therefore the duration of induced HPV immunity needs to be at least ten years after adolescent vaccination to protect against persistent HPV infection and subsequent development of moderate to severe abnormal cervical changes.

Current evidence from clinical trials suggests sustained immunity up to five years with no evidence of reducing. Continued monitoring of longevity of immunity is underway.

Safety of vaccines

These vaccines are both generally well tolerated with the most common adverse event being local discomfort at the injection site. There have been no discontinuations in trials due to adverse events.

Common issues with HPV vaccines

All sexually active women are at risk

HPV is very common, and while highly sexually active women are at higher risk of contracting HPV earlier, all sexually active women are at risk. Advice about practising safe sex should still be provided; it is important that women realise that the vaccine does not protect against all types of HPV or other sexually transmitted diseases.There have been parental concerns expressed around adolescent HPV vaccine promoting promiscuity or earlier sexual activity. To date there is no evidence for this.

Vaccination most effective prior to sexual debut

There is currently no evidence that these vaccines have any therapeutic activity against persistent HPV infection. Consequently, for preventative vaccination to be most effective, it should occur prior to sexual activity.

Age of vaccination

Early adolescent girls have been shown to have a better response to the HPV vaccine compared with older women. This could theoretically lead to longer lasting immunity. However, there is no definite evidence of this.

Vaccination of males

The added value of vaccinating males to attempt herd immunity is currently not clear.

Summary

HPV vaccination can be expected to reduce cervical cancer and possibly a range of other cancers. Vaccines appear to have good safety profiles to date, and duration of immunity is at least five years with ongoing monitoring.

Effectiveness is highest if given to females prior to exposure to HPV; hence the best age to deliver this vaccine is expected to be in the early adolescent period. There are significant implications for community awareness and education around the role of HPV in cervical cancer, the fact that it is a sexually-transmitted disease, and sustaining an ongoing high-quality
cervical screen.

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