A trial of the new cervical cancer vaccine programme for schoolgirls across the country has encountered opposition from parents, with 20% refusing to give permission for their daughters to have the jab.

A third of those who gave a reason for refusal said they were worried about the long-term safety, on which there is no data. But some may have concerns that allowing vaccination may promote promiscuity, because the cancer-causing virus which the vaccination targets is passed on in sexual intercourse. Two schools declined to take part for religious reasons.

The findings from the pilot study, involving 2,817 girls aged 12 and 13 in year 8 at 36 secondary schools in Greater Manchester, are published by the British Medical Journal today. In an accompanying editorial, Professor Jo Waller and Dr Jane Wardle from the department of epidemiology and public health at University College London say 12- and 13-year-old girls whose parents refuse consent may be competent to decide for themselves.

The £100m vaccination programme, which targets strains of the human papilloma virus (HPV) responsible for most cases of cervical cancer, is due to begin in schools across the UK in September for 12- and 13-year-olds, followed by a catch-up programme for girls up to 18. The pilot began in February last year, with two out of 10 primary care trusts agreeing to take part. Parents were sent information, consent forms and reminders.

Uptake was significantly lower in schools with a high proportion of girls from ethnic minority groups and those entitled to free school meals.

Wardle and Waller said that in the wake of the MMR controversy, "work needs to be done to restore public confidence in immunisation".