MANILA – In a position paper released the previous weekend, the World Health Organization (WHO) supported vaccination against dengue in countries with a high occurrence of the illness.

The paper was welcomed by the Department of Health (DOH), which earlier this year implemented a controversial anti-dengue vaccination program for Filipino children.

(READ: DOH to start dengue vaccination Monday)

Dengue vaccine CYD-TDV or Dengvaxia® was first registered in December 2015 and has since been used in several countries, including the Philippines.

However, the WHO warned against vaccination in countries with low instances of dengue, because the vaccine can be ineffective and may have potential harmful side effects, especially in children under nine years of age.

According to the WHO, vaccination should also be part of a government's comprehensive dengue control strategy.

The DOH already vaccinated children in Regions III, IV-A, and the National Capital Region. Children enrolled in fourth grade (at least 9 years old) in public schools received the shots. More than 489,003 children were inoculated against dengue from April to July 2016.

(READ: PH spending P3-B on dengue vaccines)

According to Health Secretary Paulyn Jean Rosell-Ubial, they are monitoring the effectiveness of the vaccine due to earlier reports that the current vaccine is not reliable against certain common strains of dengue.

This can be due to infection prior to vaccination and exposure to the illness’ strains can affect how effective a vaccine is, she said.

Earlier this year, the DOH’s vaccination program received flak from health advocates who decried it as "rushed", and the vaccine potentially harmful.

(WATCH: Expert raises concern over safety of dengue vaccine)

In 2015, the Philippines became the first Asian country to approve the sale of the world's first-ever dengue vaccine.