Thursday September 20 2007
Vaccination could stop spread of HPV
A study on how common the human papilloma virus (HPV) is in young women in England has been reported by multiple news sources. “One in 10 girls under 16, the age of consent, has a sexually transmitted disease that leads to cervical cancer”, The Daily Telegraph reported.
The Daily Mail said “The risk a girl is carrying the HPV virus rises ‘substantially’ after the age of 14 – two years before they can legally have sex”. This has prompted “calls for children to be vaccinated against the virus before they become sexually active” stated The Times.
The reports are based on a study that was presented alongside expert commentary and estimates of the economic impact of vaccinating girls against HPV. Most headlines reported the prevalence (see glossary) of HPV in girls by the age of 16. The overall rate was correctly reported as one in 10, which is the new finding of this research.
The Department of Health is currently considering a policy of vaccinating girls against this disease and these results will help inform future decisions over what age any national immunisation programme should start. The vaccine needs to be given to girls before they are infected with the HPV virus for it to be effective, The Daily Telegraph states that the researchers recommend introducing “an immunisation programme for girls from the age of 12”.
It is likely that this work will be used to inform recommendations to the Department of Health about national immunisation policy, subject to its approval by a panel of public health experts.
Where did the story come from?
Dr Mark Jit and colleagues from the Health Protection Agency (HPA) in London reported this research. The study was funded by the Research and Development Directorate of the UK Department of Health. The study was published as a ’Short Communication‘in the peer-reviewed medical journal British Journal of Cancer. Results from this study and the associated modelling work done by the HPA were presented back-to-back in 20-minute talks at the annual Health Protection conference in Warwick on September 19 2007.
What kind of scientific study was this?
This was an observational study that estimated the rates of infection with four different HPV strains in women of different ages, by examining stored blood samples collected from young women in England.
The researchers obtained 1,483 blood samples that had been submitted for routine tests from laboratories across England. The age of the women was known, and ranged from 10 to 29 years, but other details were not. Samples were tested for antibodies to four strains of HPV virus (6, 11, 16 and 18). The presence of the antibodies indicates that the women had been exposed to these strains of the virus.
The researchers tested blood samples and calculated the age-specific rates of antibodies to these strains of virus for young women in 12-month age bands between the ages of 10 and 29 years.
The overall prevalence was adjusted to reflect the numbers of women in each age group across the population in England in 2004 (age-standardised rates). This step is important, as the proportion of young women in each age group in the sample might not reflect the proportion in the general population, so suitable adjustments were made in order to estimate rates in the population as a whole.
What were the results of the study?
The age-standardised prevalence
of any of the four virus strains across the whole population was 20.7%. Other important results were that less than 5% of girls under the age of 14 were positive for any of the virus types and the prevalence increased sharply from the age of 14 years onwards.
What interpretations did the researchers draw from these results?
The researchers suggest that these new data “offer an additional viewpoint on the epidemiology of HPV in England” and that the significant prevalence of positive blood tests for HPV at younger ages than previously thought, particularly before the ages typically offered cervical screening, has implications for the age at which vaccination should be delivered.
What does the NHS Knowledge Service make of this study?
This is a key piece of research for informing any future decisions about exactly how any vaccination programme targeting HPV in young women should be designed and run. Other pieces of the jigsaw will be required for estimating the potential impact and cost of any proposed programme of vaccination:
- The effectiveness of the vaccine over the long-term (decades) will need to be evaluated to answer the question: will the incidence of abnormal cervical smears, or cervical cancer, fall following the immunisation programme?
- Two costs will also form part of any modelling: the costs of delivering the vaccination programme, and the savings made by avoiding treatments for abnormal cervical smears and treating cancer itself.
The Health Protection Agency has begun this work and acknowledges some of the uncertainty around estimating these factors.
Sir Muir Gray adds...
The NHS Cervical Screening Programme has saved many lives and is an effective form of secondary prevention, namely prevention by the early detection of a disease before it causes symptoms.
Primary prevention – stopping the disease before it starts – is always better than secondary and it is now possible to lower the risk of cervical cancer by immunising against the strains of HPV that cause the disease.
Public health programmes, like medical treatments, have costs and risks, as well as benefits, so it is important to decide precisely what the optimum vaccination programme would be. This study suggests that immunising at the age of 14 would reduce the effectiveness of the programme.