Dengue Vaccine

Dengue is a mosquito-borne viral infection.
Dengue virus is transmitted by female mosquitoes mainly of the species Aedes aegypti and, to a lesser extent, Ae. albopictus.
These mosquitoes are also vectors of chikungunya, yellow fever and Zika viruses.
Dengue is found in tropical and sub-tropical climates worldwide, mostly in urban and semi-urban areas.
The virus responsible for causing dengue is called dengue virus (DENV) which belongs to the Flaviviridae family. There are four DENV serotypes, meaning that it is possible to be infected four times.

Dengue is a severe, flu-like illness that affects infants, young children and adults, but seldom causes death.
Symptoms usually last for 2–7 days, after an incubation period of 4–10 days after the bite from an infected mosquito.

There is no specific treatment for dengue fever.
Fever reducers and pain killers can be taken to control the symptoms of muscle aches and pains, and fever.
In 2021, India reported 110,473 dengue cases, ranking fourth among the worst-affected nations.

Why in News?

With the expanding geography of dengue infections — in India as well as the world — an increasing need has been felt for an effective vaccine that can protect against all four serotypes.
Nearly half the population of the world lives at risk of the disease at present.

Vaccine in human trials

At present, there are three vaccine candidates that are being tested in humans in India.
First, a vaccine developed by Panacea Biotec based on live weakened versions of the four dengue serotypes developed by the National Institute of Allergy and Infectious Diseases in the United States. The US laboratory developed weakened versions of all four dengue virus serotypes — they deleted parts of the genetic code of DENV1, DENV3, and DENV4 serotypes of the virus to do so and then genetically engineered DENV2 backbone using parts from weakened DENV 4 on which the others were tacked on. These were grown in cell culture by Panacea Biotec to develop the vaccine.

There are at least two indigenous vaccines against dengue under development in research institutes.
One of the main challenges of developing a dengue vaccine is antibody-dependent enhancement (ADE) — a person with low levels of antibodies against one serotype of dengue, may end up getting a more severe infection with another serotype of dengue.
This was what led to controversy surrounding the first dengue vaccine to be approved. Only after a vaccination programme had been rolled out in the Philippines, it was found that the vaccine could actually increase the risk of severe disease in people who had not been infected before.
To do away with this problem, both the Indian research teams selected a specific part of the envelop protein known to not cause ADE. The vaccines were shown to offer almost 100% protection against all four serotypes. This has been tested in mice and monkeys but is yet to be tested in humans.

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