Plans to vaccinate young girls against the sexually-transmitted virus that causes cervical cancer have been blocked in several US states by conservative groups, who say that doing so would encourage promiscuity.

Advocates of the vaccine point out that the jabs work against human papillomavirus (HPV) - which causes virtually all cases of cervical cancer - and are safe.

The latest data from a large clinical trial of Merck's cervical cancer vaccine, Gardasil, found it offered 100% protection against cervical, vulval and vaginal diseases, caused by HPV (types 6, 11, 16 and 18) and 98% protection against advanced pre-cancers caused by HPV types 16 and 18 (New England Journal of Medicine: vol 356, p1915).

After around three years of the four-year trial, almost all girls who received the vaccine before being exposed to HPV 16 or 18 appear to be protected. Those who had already been exposed to the viruses received little benefit, but by vaccinating early on, perhaps at 11 years of age, most girls could be protected.

Controversial care

However, the introduction of a vaccine against HPV types 16 and 18, which together cause 70% of cervical cancer cases, has been dogged by arguments. Some conservative groups complain that by cutting the risk of catching a sexually-transmitted disease, the vaccine would encourage sexual activity in young girls.

Earlier data from the same trial had already led the US Centers for Disease Control and Protection (CDC) to recommend that 11-12 year-olds be vaccinated.

However, attempts to introduce compulsory vaccination programmes at the state level have run up against opposition. Four states - West Virginia, Kentucky, Mississippi and New Mexico - have rejected vaccine programmes. In Texas, governer Rick Perry suffered embarassment last month when his order requiring schoolgirls to be vaccinated was blocked by the state Senate. Only one state - Virginia - has so far passed a law requiring vaccination.

But the new results, which include extra data showing a lack of side effects, could influence the debate in the 15 states, all in central and eastern part of the US, where legislation is still on the table. In the meantime, some states are opting for less controversial voluntary programmes. In New Hampshire, where the shots are on offer to girls aged 11 to 18, several clinics are reported to have run out of stock.

Premature reaction?

Public health experts are also divided, though. Some question whether the relatively small numbers of lives that would be saved are justified by the significant cost of a vaccine programme. Merck will charge around $360 for the three-doses needed.

George Sawaya, a gynaecologist at the Comprehensive Cancer Center at the University of California, San Francisco, notes that the trial still has another year to run. Surprises often appear late on in such studies and Sawaya says he thinks the CDC should have waited until all the data was available before taking a stance on the vaccine.

The trial's impact may be better felt in developing nations, where the screening programmes that have already cut deaths in richer countries are often too expensive to implement.

The GAVI Alliance, a public-private partnership that spends around $300 million annually on vaccination programmes in poor countries, is considering funding HPV shots.

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