Healthcare professionals here have been issued advisories on a dengue vaccine which could be harmful to people not previously infected by the virus.

The Health Sciences Authority (HSA) said in response yesterday to queries from The Straits Times that all healthcare professionals here have been issued advisories on the vaccine, Dengvaxia.

The authority added that it will further strengthen the warnings and recommendations in the prescribing information of the vaccine, as well as closely monitor it to ensure its continued safety and efficacy.

The manufacturer, French pharmaceutical giant Sanofi Pasteur, said Dengvaxia was found to have a possible harmful effect when used on people who did not previously have dengue. Those who were vaccinated and later became infected could have "more cases of severe disease", Sanofi said last month.

When asked, HSA said there was one report of a male patient who developed a rash three days after being vaccinated, but he has since recovered. It has had no other reports of adverse reactions to Dengvaxia.

The world's first dengue vaccine, Dengvaxia has been available in Singapore since March, after HSA approved its use in patients between 12 and 45 years old in October last year.

Back then, HSA flagged the potential risk of severe dengue after reviewing data from Sanofi. It informed healthcare professionals of the risk and recommended that patients consult doctors before getting the vaccine. Educational materials and the package insert of Dengvaxia carried information on the risk.

Blood tests to identify previous dengue infection were also made available at major hospitals here.

HSA said it is now working with Sanofi to "strengthen the package insert" to include a warning of an increased risk of hospitalisation for dengue and clinically severe dengue in vaccinated people not previously infected by dengue.

However, in its alert, Sanofi had added that for those previously infected, Dengvaxia "provides persistent benefit against dengue fever".

HSA noted that dengue vaccination is not part of the national immunisation programme, meaning the vaccine is given to individuals only when the benefits outweigh the risk.

SEE WORLD