Defeating dengue

A long awaited vaccine for the deadly virus has finally arrived — but Thailand is yet to approve it

After more than two months waging war against the severe form of dengue fever, Channel 3 actor Thrisadee "Por" Sahawong eventually succumbed and passed away last Monday at Ramathibodi Hospital.

Put aside public sorrow, we must admit that Thrisadee's lengthy fight with deteriorating complications -- from serious infection which led to him having his left foot amputated to the removal of his left lung -- has significantly raised public awareness regarding this mosquito-borne viral disease that has wreaked havoc in 128 countries, according to the World Health Organization (WHO). More than 142,000 Thais were reported to have contracted dengue fever last year, with 141 deaths. Thai officials have also warned that the figures are likely to increase in 2016. 

People around the globe, especially in countries at risk, have been looking forward to a vaccine to immunise themselves against the dengue virus given there is no specific treatment for the disease. Finally the wait is over.

The world's first dengue vaccine is now available and has so far been approved in three countries. Mexico is the first nation to have allowed the sale of the vaccine, followed by the Philippines -- Asia's first country to join the dengue vaccine bandwagon. Brazil became the third in the world to authorise such a prevention method. The vaccine is developed and manufactured by French pharmaceutical company Sanofi.

Professor Usa Thrisyakorn, professor of paediatrics at Chulalongkorn University and chairman of the Asian Dengue Vaccination Advocacy (ADVA) group, said that the world's first dengue vaccine is indeed a major life-saving medical breakthrough for people globally.

"After 70 years of waiting, this really is a piece of good news," said Dr Usa in an interview with Life as part of the Asian Dengue Summit organised earlier this month at Shangri-La Hotel.

According to Dr Usa, the world's population is currently in desperate need of something to shield themselves against the dengue virus given patterns of the outbreak have become harder and harder to predict. In the past, the pattern was quite foreseeable -- like an outbreak once every two years. But now climate change has significantly impacted on transmission of the virus. It can spread every year or all year round which means prevention is crucial.

"The global climate has changed and this is an issue we must be vigilant over. When it still rains in months that are supposed to be cold, this suggests something. Mosquitos lay eggs in standing water left by heavy rains. If a lot of dengue-infected cases are still reported during winter months in this country, it can be predicted that there could be a major outbreak in the following year," said Dr Usa, also adviser of the Faculty of Tropical Medicine, Mahidol University.

This dengue vaccine, according to Dr Usa, is called chimeric yellow fever–dengue virus tetravalent dengue vaccine or CYD-TDV -- a combination of the weakened form of yellow fever and dengue fever viruses. This CYD-TDV vaccine is claimed to be able to protect against all four strains of dengue virus, namely DEN-1, DEN-2, DEN-3 and DEN-4. It is, however, unable to serve as protection against yellow fever.

For the vaccine to take full effect, three doses are required to be administered over the course of one year, the second jab six months after the first one and the last shot six months later. According to the ADVA chairman, the vaccine is able to reduce the chance of contracting the dengue virus by 60%. For those infected, it can lessen the severity of symptoms by 80-90%.

Prior to vaccine approval, clinical studies were conducted with 30,000 volunteers which involved kids aged two to 14 in Asia and nine to 16 in South America. It was found that the vaccine is highly effective when used in children aged above nine.

"The food and drug administrations in the three countries [which have authorised the sale of the vaccine] have approved the dengue vaccine for people aged nine to 45," explained Dr Usa. "For those younger or older than the aforementioned age, more research and follow-ups are required to see if it yields satisfying results. But one sure thing is that there are medical studies to ensure that the vaccine is safe regardless of the age of people who are to get the shot."

But because the vaccine's clinical trials have so far been followed up for four years, researchers are not yet able to pinpoint as to how long the vaccine could take effect. But during these four years, those who received the shot are strongly immunised against the virus.

In Thailand, the Food and Drug Administration (FDA) still needs some more time to review studies and efficacy of the vaccine before approving the sale.

"It all depends on our FDA," commented Dr Usa. "The Administration has a set of strict protocols which is a very good thing. Even though there are medical studies to back up the vaccine's effectiveness, they need to be re-examined by the FDA for safety reasons." In the meantime, the ADVA chairman is of the opinion that regional collaboration is key both in terms of public health management and the vaccine's cost-effectiveness. Dr Usa referred to the bargaining power of the Pan American Health Organization (PAHO), a public health collaborative agency which improves health for countries of the Americas.

"These member countries [of PAHO] get together and subsequently they can buy vaccines at a lower price. It would be ideal if there was a similar kind of public health agency in Asia," she said.

And while the dengue vaccine is not yet available in Thailand, Dr Usa suggested that the country follow the WHO's public health protocols for dengue fever management.

"Medical practitioners must do their best to take care of patients and to prevent mortalities," she noted. "Then surveillance must be carried out. Only effective mosquito control methods must be put in place. In case the dengue vaccine is approved, a post-injection monitoring process is crucial. Last but not least, medical studies and research must be conducted continuously for public health and dengue control improvements.

"Thailand is well known for its medical research. We have been recognised on a global scale that we are highly experienced when it comes to handling dengue fever. So I wish in the near future to see our country's healthcare sectors do better in preventing more dengue-infected cases by using this tool that will soon be available."

Fever facts

390 million dengue infections occur each year

Half of the world's population are at risk of dengue infection

740 people are infected by dengue per minute, globally

Asia has the highest dengue burden globally with around 67 million people contracting the disease each year

Over 142,000 Thais were reported to suffer dengue fever last year. 141 died. This is a sharp increase from 2014 when only about 40,000 Thais were found to be infected and only 41 died

The Department of Disease Control under the Ministry of Public Health predicts that dengue-infected cases are likely to reach 166,000 this year. Up to 7,500 cases are expected each month and the monthly number could reach 25,000 during rainy season (June to August)

Information from the WHO, the ADVA and the Department of Disease Control.

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