Dengue vaccine now within sight, but Bangladesh decides to wait and see

• Indonesia to roll out vaccine next year
• Some other nations also consider approving it 
• "Qdenga" is yet to receive WHO approval 
• In market, Sanofi's Dengvaxia is lone approved shot 

After years of research, Japan's pharmaceutical giant Takeda Pharmaceutical Company has developed a dengue vaccine named "Qdenga" – offering hope for future generations. 

Indonesia has already approved the vaccine, which is expected to hit the market in early 2023. Besides, a number of other countries, including the USA, have been considering approving the drug.

But Bangladesh has so far shown little or no interest in the shot as the country says it focuses on preventive measures on the war against the mosquito-borne disease. 

Besides, the authorities say they are keeping tabs on vaccine updates in other countries and how the World Health Organization (WHO) responds to it.

Bangladesh has been going through its worst dengue outbreak this year. As of Wednesday, 187 people have died of dengue infection, which is the highest number of fatalities in the last 22 years.

"Any new vaccine involves huge costs and other issues, such as how long it would offer protection. For example, if the new dengue vaccine offers protection for four years, we will have to put it in the national inoculation plan, which is a lengthy process," Prof Dr Ahmedul Kabir, additional director general of the health directorate, told The Business Standard.       

"This is not feasible at the moment. Rather, let's observe how it performs after hitting the market," he added. 

Prof Dr Nazmul Islam, director of the Communicable Disease Control unit of the health directorate, said there has been no official discussion on dengue vaccines in any forum so far. 

"Since we take WHO as the standard, the matter will be discussed if WHO gives any guidelines on the vaccine," he told The Business Standard.

Prof Nazmul said the health authorities will have to ensure first whether the vaccine is efficient enough against all four serotypes of dengue virus.  

Indonesia approved Takeda's Qdenga in August, and the company says it will start selling it there early next year. 

In October, a European Union advisory panel said Qdenga can be administered to people as young as four years old, a recommendation that could lead to EU consent within a few months. And the company is seeking approvals in about a dozen other countries, including the US.

"Dengue disease burden in Bangladesh is less compared to countries where dengue outbreaks are more frequent, such as Indonesia, the Philippines and Singapore. Besides, a large proportion of dengue cases in Bangladesh are only in metropolitan cities. So we have scope for going slow about the vaccine," said Prof Nazmul Islam.

He emphasised checking mosquito breeding during the monsoon to contain the situation and to bring dengue cases under control.  

In 1997, the French multinational pharmaceutical and healthcare company Sanofi began its work on a dengue vaccine and won Mexican approval for what it called Dengvaxia in 2015. 

The vaccine was soon introduced in 19 countries. But a later study, which was confirmed by Sanofi's, found that in rare cases, Dengvaxia can backfire. In people who never had dengue are vaccinated and later become infected, the vaccine may provoke a much more severe form of the illness.

Takeda's path to Qdenga began in 2013 when it bought Inviragen Inc., a company in Colorado that had been working on the vaccine. Proving its efficacy and safety was complicated because dengue can be caused by four distinctive strains, and protection must be built against all of them. In some cases, patients who are reinfected with a different strain can suffer more severe symptoms because the neutralising antibodies generated from the first infection may bind themselves to the virus and increase its ability to enter cells. 

Although it is not clear, some researchers say a similar pattern may occur in vaccinated people — possibly the root cause of Dengvaxia's difficulties.

Takeda's two-shot immunisation is based on what is called the serotype 2 variant, with components of the three other strains attached. In a trial involving 1,800 young people in the Dominican Republic, Panama and the Philippines, the drug induced an immune response against all four strains that lasted at least four years after the injections.

That result allowed Takeda to proceed to a test involving more than 20,000 participants in Asia and Latin America. The vaccine cut hospitalisations of recipients by 84% compared with a placebo and prevented the illness in 61%, with no significant safety risks. Although the vaccine is not equally effective against all four strains, Christophe Weber, Takeda's chief executive officer, says, "What is important is to look at the overall efficacy".

Dr Kabirul Bashar, a medical entomologist and professor of zoology at Jahangirnagar University, told The Business Standard that Takeda's vaccine is different from Dengvaxia. 

"Though the vaccine has not yet received WHO approval and we are not buying it anytime soon, we should keep in touch with the vaccine maker," he added.