Dr Muris Houston: There is no evidence to warrant an HPV vaccine scare
A court case has sparked worry about the safety of the human papilloma virus vaccine. How does it work, and how effective is it?
Gardasil vaccination: more than 644,000 girls in Ireland have been inoculated. Photograph: Joe Raedle/Getty
The benefits and side effects of the vaccine for the human papilloma virus are back in the news this week because of a High Court case taken by a member of a support group of parents who claim that teenage girls have become ill after being injected with it. The group is seeking the withdrawal of the licence for Gardasil, the version of the vaccine administered as part of the national immunisation programme.
Introduced in the Republic in 2010 on the recommendation of the World Health Organisation, HPV vaccination is primarily aimed at preventing cancer of the cervix.
Almost every case of cervical cancer – about 99 per cent – is estimated to be caused by persistent infection with certain strains of HPV. Eighty-five per cent of girls in first year of secondary school received the three-dose course in the 2013-4 school year.
HPV can infect and damage cells on the surface of the cervix, which can lead to the development of precancerous lesions over a number of years. These lesions, known as grade-two or -three cervical intraepithelial neoplasia, are the precursors of cervical cancer. Screening programmes aim to pick up these changes at the precancerous phase. But the discovery of a vaccine for HPV offers the chance to prevent infection before women become sexually active.
Gardasil is more than 99 per cent effective in preventing precancerous lesions associated with HPV types 16 and 18, the two cancer-causing subtypes that account for 70 per cent of cervical-cancer cases.
A major public-health reason for national immunisation programmes is the “herd immunity” effect, whereby a vaccine’s protective effect extends beyond the vaccinated individual to others in the population.
Herd immunity is a sought-after aim in all immunisation programmes. If enough people are vaccinated, the overall prevalence of an infectious agent in the population drops to a level where even those who are not vaccinated benefit from the diminution of cases of disease in the community as a whole.
Australian researchers were able to demonstrate the beginnings of herd immunity attributable to the HPV programme, which has led to an 82 per cent reduction in genital warts diagnosed in young heterosexual men in Australia, even though they were not targeted in the original phase of a national HPV vaccination programme.
So these are benefits of the HPV vaccine. What about its side effects? As with most vaccines, a reaction where you were injected on your arm is quite common. Fainting is not unusual. But allergic reactions to cervical-cancer vaccine are rare, according to a study of Australian schoolgirls immunised since April 2007.
Other relatively common side effects, affecting more than 1 per cent of recipients, include headache, fever and nausea. Less frequently, about one girl in 10,000 who have the HPV vaccine experience an itchy red rash. Very rare side effects, affecting fewer than one person in 10,000, include some degree of airway narrowing.
But the European Medicines Agency has just reviewed the evidence relating to reports of two conditions, complex regional pain syndrome and postural orthostatic tachycardia syndrome in young women given HPV vaccines. It found no evidence to link either syndrome with the vaccine.
Postural orthostatic tachycardia syndrome is a condition in which the heart rate increases abnormally on sitting or standing up, accompanied by dizziness, faintingor weakness, among other symptoms, as well as headache, aches and pains, nausea and fatigue.
No medical intervention is completely free of side effects, but there is no evidence at present to warrant an HPV vaccine scare.