The Philippines’ Department of Health (DOH) is on high alert after French pharmaceutical giant Sanofi Pasteur announced that its first-ever approved Dengue vaccine, Dengvaxia, has potentially adverse effects.

“The analysis confirmed that Dengvaxia provides persistent protective benefit against dengue fever in those who had prior infection. For those not previously infected by dengue virus, however, the analysis found that in the longer term, more cases of severe disease could occur following vaccination upon a subsequent dengue infection,” the company wrote in its announcement on Nov. 29.

“These findings highlight the complex nature of dengue infection. We are working with health authorities to ensure that prescribers, vaccinators and patients are fully informed of the new findings, with the goal of enhancing the impact of Dengvaxia in dengue- endemic countries,” Global Medical Head of Sanofi Pasteur, Dr. Su-Peing Ng, said in the statement.

“The Department of Health is prepared for a worst-case scenario,“ DOH spokesman, Eric Tayag, told AFP via local news network ABS-CBN.

The announcement comes after the government put a halt on its immunization program, where more than 733,000 children ages nine and older have already been injected with the Dengvaxia.

“They are being followed up for adverse effects following immunization,“ he continued.

Most of the children who were given the vaccine are from places where dengue is already widespread. Tayag added that the DOH is monitoring hospital records of people who have severe cases of the virus.

So far, there have been no reported deaths related to the dengue vaccine in the Philippines, Sanofi said during its press conference on Monday, BBC reported.

“As far as we know, as far as we are made aware, there are no reported deaths that are related to dengue vaccination. Of course, rest assured, monitoring is continuing, we are working with the Department of Health (DOH), in collaboration, to make sure this is maintained,” Sanofi medical director, Ruby Dizon, said at the conference.

Dengue is a mosquito-borne viral infection which causes flu-like symptoms, and can sometimes develop into a potentially life-threatening illness.

According to the data gathered by the DOH, more than 1,000 people have died from the disease last year. The figure is more than 50% higher than the recorded fatality rate in 2015, which was at 647 at the time, Philippine Star reported.

The data showed that the death rate of dengue was higher among children in the one-to-four years age group.

Meanwhile, the total number of patients infected by the virus transmitted via mosquito bite have dropped to 211,108 last year, compared to the 213,930 recorded cases in 2015.

There have also been a considerable decrease of dengue cases in the first half of 2017, with only 43,770 cases reported for January 1 to July 1, 36.8% lower than the 69, 297 recorded during the same timeframe in 2016, according to the Manila Times.

Two hundred fifty deaths were reported among the 43,770 cases, 84 fatalities less than the 334 during the same time period in 2016.

Featured Image via Wikimedia Commons / James Gathany CDC