SINGAPORE, April 3, 2009 (AFP) - Singapore Friday called for caution on carrying out mass immunisation of girls as young as nine years old against cervical cancer, saying the vaccine's effects must be studied further.

Balaji Sadasivan, senior minister of state for foreign affairs, said the vaccine against the human papillomavirus (HPV) which causes cervical cancer was already available in the city-state.

Parents can decide whether they want to vaccinate their daughters but the government "should be more circumspect about recommending the vaccination for inclusion into the childhood immunisation programme," he said.

Sadasivan, a surgeon and former senior minister of state for health, told a meeting of cancer specialists there were concerns from clinical as well as ethical standpoints.

"We do not know if the vaccine will confer long-term immunity or would immunity wane after some years," he said in a speech to the Asian Oncology Summit.

"We do not know if other types of HPV will become dominant after we contain the current strains of HPV."

Since HPV is a common virus spread through sexual contact, he also said a mass vaccination programme could send a message that teenage sex was condoned.

"I'm not saying it's wrong or right but I think it's a question of measuring risk benefit for the country. Individual parents can make the decision, but for a national programme I think we have to be a little bit more cautious," he told reporters after his speech.

Pap smear tests remained the safest way in detecting and preventing cervical cancer, he said.

In February, Spanish health authorities withdrew tens of thousands of doses of a vaccine against cervical cancer after two teenagers who received the shots were hospitalised.

Other countries are going ahead with mass immunisations.

Sweden said last year it would offer vaccines against cervical cancer to all primary school girls as part of the country's free vaccination programme.

Cervical cancer ranks second to breast cancer as the most common cancer among women in the Asia-Pacific region, data released at the meeting showed.