Tuesday March 1 2011
Some have called for boys to get the HPV jab currently given to girls
The Daily Mirror has reported that “experts are calling for boys to be vaccinated against the human papilloma virus (HPV) after a study has found that 50% of men are infected with the virus”. Some strains of HPV have been linked to cancers, including cervical cancer in women and cancers of the penis, oral cavity and anus. Some strains also cause genital warts in males and females.
The news is based on an international study which checked 1,159 men for the virus every six months for over two years. The research in Brazilian, Mexican and American adults looked at rates of new infections and how quickly the men cleared their infections. It reportedly found that each year 6% of men acquire the cancer-causing strains of HPV. It also found that having a higher number of female and male sexual partners was linked to a higher risk of infection.
Understanding the rates at which HPV infections occur and clear is useful for developing potential strategies for male HPV vaccination. However, on its own this research does not justify vaccinating all UK boys against the virus, particularly as the study looked at foreign adults. Assessing the case for male HPV vaccination will require careful consideration and further data to see if the potential benefits would justify the costs.
Where did the story come from?
The study was carried out by researchers from H Lee Moffitt Cancer Centre in Tampa, Florida; the Ludwig Institute for Research on Cancer in Brazil, and the National Institute of Public Health in Mexico. It was funded by the US National Cancer Institute and was published in the peer-reviewed medical journal, The Lancet.
The newspapers have covered the research itself well, but their claims that boys should be given the HPV vaccine oversimplify the issue: establishing a vaccination programme is a complex process. Decisions about who should be vaccinated must consider whether the benefits for individuals and the population justify the costs involved. This type of planning work was carried out prior to setting up the national HPV vaccination programme for girls in this country. Also, while the media has suggested that the study lends further weight to the case for vaccinating UK boys, the research evaluated the prevalence and incidence of disease in adult males in overseas populations.
What kind of research was this?
HPV is readily transmitted during sexual intercourse. The researchers say that it is important to understand the infection in men because male sexual behaviour affects rates of HPV infection and disease in female partners. A vaccine has been developed to reduce HPV-related diseases in women but there is limited research to inform us of its benefits in men. Researchers in this study set up a cohort study called the HPV in Men (HIM) study to determine the course of the disease in adult males in three countries: Brazil, Mexico and the US.
What did the research involve?
The study included adult men with no current or previous diagnosis of anal or penile cancers, and no current or previous diagnosis of genital warts. They were recruited via:
- a clinic providing genitourinary services and population-wide advertising in Brazil
- a health plan in Mexico that serviced factories and the military
- a university, and from the general population in Florida
The intention was to assess the participants every six months for four years. At each assessment, swabs were taken from the penis and scrotum to detect whether there was any infection with HPV and which strains were present. On each occasion, the participants also completed a self-report questionnaire about their sexual behaviour.
Swabs from a total of 1,159 men were available for analysis. They were divided into three age groups: 18 to 30 years, 31 to 44 years and 45 to 70 years. Their average age was 32 years. The majority were sexually active, heterosexual, white, uncircumcised and non-smokers. The men were reported to be given ‘compensation’ to encourage their participation, although the study paper does not provide any detail on this process. However, only 10% of the starting population completed three years of follow-up.
From the wealth of data collected, the researchers assessed the rate of new infections with HPV and how long it took men to clear their infections. Infections were classified as positive if any of the swabs tested positive for one or more of 37 HPV strains. Infections were further grouped into oncogenic infections, i.e. with a strain that causes cancer. Infections with other types were classed as non-oncogenic. Researchers also performed separate analyses to determine the rate and prevalence of infection with HPV16, the strain known to cause cervical cancer in females.
Men who were free of any HPV infection at the study start were included in the analyses assessing rates of new infection. Those with an infection at the start of the study were included in analyses determining the rate of clearance of infection, i.e. how long it took after a positive test for a man to have two consecutive negative tests.
The researchers determined which factors were linked to infection based on the information collected through questionnaires. They conducted subgroup analyses to see whether rates of infection were different according to country, smoking status, education, the number of lifetime sexual partners and whether the participant had male anal sex partners in the previous three months.
What were the basic results?
In total, 50% of the men were infected with HPV at the start of the study. During follow-up, new genital HPV infection occurred at a rate of 38.4 per 1,000 person-months. Men reporting at least 50 sexual partners were at twice the risk of having a cancer-causing HPV infection than men reporting no more than one partner. Having more than three recent male anal sex male partners also more than doubled the risk.
There was little difference across the age groups in the rate of new infection. Any HPV infection lasted about seven and a half months in men. Infection with the cancer-causing HPV16 lasted more than a year on average.
How did the researchers interpret the results?
The researchers conclude that the study provides much-needed data about the incidence and clearance of HPV infection in men. They also conclude that the data is essential for the “development of realistic cost-effectiveness models for male HPV vaccination internationally”.
This was a large cohort study of men from selected populations that gives some insight into the burden of HPV infection in men. It does not assess the effects of vaccination in this population, but rather it investigates how the disease occurs in males. The researchers state that the way in which the participants were recruited to the study means that the findings may not be generalisable to the wider population, even within the countries from which these samples were drawn.
On the basis of this research, some news sources have argued that boys should be vaccinated against HPV, just as girls under the current national HPV vaccination programme introduced in 2008. The vaccine is largely given to girls aged 12 to 13 years through their secondary schools. Vaccination is also offered to girls aged 14 to 17 in a catch-up programme. While scientists have considered vaccinating boys too, the argument against has often been one of cost-effectiveness, i.e. that the benefits of vaccinating males may not justify the costs.
This new research provides important information about the incidence of new HPV infections in men and how long it takes them to clear the infections. These types of data points are important for developing cost-effectiveness models that can be used to assess whether it is worthwhile introducing population-wide male HPV vaccination programmes.
The study data provided by this research is useful and informative, but it should be remembered that most cancers caused by HPV occur in females, who therefore stand to benefit more from vaccination on an individual level. As such, they have been a priority target for vaccination programmes in this country. Another limitation that stops this study data from directly informing the debate on vaccinating UK boys is the fact that the research looked at foreign adult males aged 18 and over: the findings of the study do not apply to adolescents and may not reflect the incidence of HPV in the UK.
Previous research has looked at the possibility of an HPV vaccination programme for boys in this country. It suggested that it would not be cost-effective: while the study provides some important data that may refine models of cost-effectiveness, it is an oversimplification to claim that boys should be vaccinated on the basis of these findings.