In absence of any specific anti-viral drug, there is no treatment for the mosquito vector-borne disease, dengue, except supportive treatment. It is no doubt a sad commentary on medical research, especially on dengue, since, according to a 2016 study, 4.0 billion people in 128 countries where aedes mosquito exists were at risk of contracting dengue. Bangladesh is a veritable dengue hotspot on the world map seeing that during this year's dengue outbreak in the country, close to 1,000 are already dead (actual fatality number as of September 30 was 989) and over 200,000 have been infected with the disease and more are getting infected every day. Only a small fraction of them are being hospitalised, though there is no guarantee that all of those hospitalised will survive. Now the situation here is grave.
Researchers, indeed, did miracle by developing vaccines in record time against coronavirus when it was still ravaging continent after continent. Though dengue virus was first discovered following the 1943's dengue outbreak in Nagasaki, Japan, progress in research to find a drug or vaccine against the viral disease cannot be said to have been impressive. More than seven decades after the dengue virus was discovered, the first vaccine was developed by Sanofi Pasteur, the vaccines division of the French multinational pharmaceutical company, Sanofi. After clinical trials, the vaccine named, Dengvaxia, got licence in 2015. Mass vaccination started among 1.0 million people in the Philippines and Brazil. But in December 2017, the vaccination programme there was suspended as it was found that people who were not previously infected by dengue ran the risk of developing severe condition after application of the vaccine, Dengvaxia. At especial risk were children aged nine to adolescents of 16 years who have not been previously infected with dengue and not living in places where dengue is endemic. It was observed that children who had no previous history of dengue infection were at serious risk, if they contracted the disease (dengue) after vaccination by Dengvaxia. In that case, they may require hospitalisation following deteriorating medical condition.
As a result, developing an effective vaccine against dengue has been facing a big challenge due to the fact that the dengue virus has four serotypes (DEN-1, DEN-2, DEN-3 and DEN-4). These are called serotypes because each of these (dengue) virus strains has different reactions with the antibodies in the human blood serum. The problem is the dengue vaccine, Dengvaxia, may give life-long immunity against DEN-1, but it will not give any guarantee against DEN-2, DEN-3 or DEN-4. Scientists believe, first-time (primary) infection by dengue causes mild condition in a patient. But if that person is infected for the second time (secondary infection) by a dengue virus of different serotype than the first one, there is the risk of developing severe disease condition. Hence the Sanofi's tetravalent vaccine (meaning effective against all four dengue viruses) is applied in three separate doses to prevent four types of dengue. Japan's Takeda pharmaceutical Company's vaccine QDENGA (TAK-003), on the other hand, gives protection against all four dengue virus serotypes.
However, the most promising development so far is coming from the National Institute of Allergy and infectious Diseases (NIAID), a wing of the US's National Institute of Health (NIH). The good news is the dengue vaccine developed at NIAID is tetravalent, that is, effective against all the four serotypes of dengue virus. Named TV005, the second phase trial of this dengue vaccine has been conducted in Bangladesh. Researchers of the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B), in collaboration with the Lerner College of Medicine of the University of Vermont, USA, are learnt to have conducted the trial in Bangladesh. The vaccine has been found effective against all four types of dengue in both children and adults.
Before this trial in Bangladesh for the second phase, the vaccine's first and second trials were carried out in the USA and Brazil. In the phase I clinical trial, researchers looked for the safety and dose of the vaccine in human participants. In the phase II clinical trial, immunogenicity (ability of human cells or tissues to provoke immune response) and safety of the vaccine are tested. In the phase III of the clinical trial, the safety and the efficacy of the vaccine are tested. Phase III trial takes a few years to complete to see that it is effective against the virus or the disease caused by it when the virus is circulating among the populace under study. It takes about a decade before giving a vaccine the go-ahead after all the trial data are assessed by the regulatory body or bodies concerned. So, the world may have to wait a few years more before the United States Food and Drug Administration (FDA) gives TV005 the approval for marketing.
In Bangladesh, senior scientist of icddr,b, Dr Rashidul Haque, led the phase II trial of TV005. The phase III trial of the vaccine will be conducted in India. The BBC Bangla, quoting Dr Haque, says, the third phase of the NIAID's anti-dengue vaccine may start soon.
But until NIH's TV005 is approved, learning from other countries' experience, including that of European Union, where existing anti-dengue vaccines such as Dengvaxia are in use, Bangladesh can try to manage the dengue now wreaking havoc on the country.
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