- While the US has approved Dengvaxia, the first ever vaccine licensed for dengue, India has rejected market authorization of the vaccine until its safety and efficacy for Indians is proved.
In focus: Dengvaxia
- Dengvaxia is the first ever vaccine licensed for dengue. The vaccine can be used for the prevention of dengue caused by all dengue virus serotypes (1, 2, 3 and 4).
- Note: A vaccine generally consists of attenuated virus which triggers the immune system to fight the virus without actually causing the disease.
- It is developed and marketed by Sanofi, a French pharma major.
- In 2015, Mexico became the first country to clear Dengvaxia in its vaccination programme, followed by Philippines in 2016.
- Since then, about 20 countries have approved dengavaxia in their immunization programmes.
Need for the vaccine
- WHO estimates 40% of the world is at risk of dengue, with around 390 million infections annually.
- Being a tropical country, Dengue is endemic to India.
- In 2017, there were 1.9 lakh dengue cases and 325 deaths in India.
- Until November, 2018, India saw 89,974 dengue cases and 144 deaths.
Concerns over Dengvaxia vaccine:
- In 2017, Philippines witnessed severe cases of post vaccination fatalities in the aftermath of a vaccination campaign, with more than 10 deaths reported.
- As a result, Philippines permanently halted the sale distribution and marketing of dengvaxia.
- Dengvaxia was found to be unsafe in cases of no history of the disease. In some cases, the vaccine actually made a dengue infection deadlier than it normally would have been in case of second infection.
- The reason for this is antibody-dependent enhancement.
- Antibody-dependent enhancement
- Say a child is infected with dengue virus for the first time, and the b-lymphocytes in the immune system make antibodies to fight the virus 1.
- Now, after sometime, if the child is infected with second infection of dengue by a different virus say virus 2, the immune system (b-lymphocytes) will release the antibodies it had developed for virus 1.
- Thus antibodies made to fight virus 1 is not effective against virus making the second infection deadly and vaccine to be ineffective.
- This is called anti-body-dependent enhancement.
US approval with conditions:
- US is the latest country to permit the vaccine, but the US Food & Drug Administration has done so with certain conditions:
- The vaccine is approved to treat patients in the age group 9-16 only.
- Further, the recipients of the vaccine must have had a previous dengue infection.
- The recipients must live in a dengue endemic area.
- India has told Sanofi that the vaccine will be allowed to be marketed in India, only after it undergo phase III clinical trials (that establish safety and efficacy of a drug) on Indian subjects.