SINGAPORE - Clinical trials for what is being touted as the world's first dengue vaccine have been underway in Singapore since 2009 but the drug is not ready for general use.

It is still too early to "definitively assess" the effects of the drug, said Parliamentary Secretary for Health Muhammad Faishal Ibrahim on Tuesday.

The drug is developed by French pharmaceutical company Sanofi.

Dr Faishal was replying Mr Christopher de Souza (Holland-Bukit Timah GRC), who asked if the vaccine was being tested in Singapore.

A Phase II clinical trial involving 1,200 patients aged two to 45 has been conducted to assess its immune response and safety, he said.

Follow-ups with the trial participants are ongoing at public hospitals.

Results from two large-scale studies in Asia and South America show the drug is less effective against the most common types of the dengue virus in Singapore. These are types 1 and 2.

It is reportedly said that a person infected with one strain of the virus could develop immunity to that version, but more serious illness may occur if the person is infected with a different strain later.

This, said Dr Faishal, means a study is needed to determine whether - in a similar vein - a vaccine that only partially protects a person from a virus could lead to more severe infection from strains against which the vaccine provides poor protection.