Explained | Why is a viable dengue vaccine not yet available Premium

The Hindu explains how dengue vaccines are developed, how many vaccines are currently under trial and the prevailing challenges with vaccine research.

The story so far: Dengue is the world’s fastest-growing vector borne disease: evidence shows over the past 50 years, there was a 30-50-fold increase in dengue cases in tropical and subtropical countries, like India. While dengue is largely accepted as an annual epidemic in several countries (impacting more than 3.6 billion people) recurring every monsoon, the face and anatomy of the disease are changing.

A new study led by researchers at the Indian Institute of Science found the dengue virus has evolved “dramatically” over the last five decades in India. A Lancet study this year drew a similar conclusion, adding that urbanisation, population growth, rising temperatures, and climate change created “conditions for the dengue vectors and viruses to multiply”. In April, Argentina saw its worst dengue outbreak in 25 years.  

There is no specific medicine or cure for dengue, making vaccines crucial in preventing infection and disease progression. However, developing a universal vaccine has remained a challenge.

Dengue is transmitted to humans by the Aedes mosquito species, A e. aegypti or  Ae. albopictus, which also spreads Chikungunya and Zika virus. There are four serotypes (or types) of the dengue virus — DEN-1, DEN-2, DEN-3 and DEN-4 — each virus interacting differently with antibodies in the human body. Each serotype is capable of manifesting into dengue fever, dengue hemorrhagic fever and dengue shock syndrome.

Five types of dengue vaccines are currently being investigated: live attenuated vaccine (which uses the weakened or “attenuated” form of the virus, such as the measles or chickenpox vaccine); inactivated vaccine (using the dead virus, used for Hepatitis A and rabies), recombinant subunit vaccine (as in COVISHIELD, where non-structural proteins of the dengue virus are used, aiding a balanced immune response), viral vectored vaccine (such as the vaccine against Ebola) and DNA vaccine (for HIV, malaria, TB).

The first documented (albeit unsuccessful) clinical trial dates back to 1929, when scientists used virus inactivated using phenol or bile; then during World War II, scientists used weakened strains of DEN-1 and passed it through mouse brain.

Sanofi Pasteur’s Dengvaxia, a live attenuated vaccine, was the first vaccine to receive a nod in 2015, and has been licensed in 20 countries (not in India) since. Other key players include Takeda’s Qdenga (TAK-003), which was recently approved in Brazil and Indonesia, and by the U.S. Food and Drugs Administration (FDA) for priority clearance in November 2022. Another live-attenuated vaccine (TV003/TV005) was developed by the U.S. National Institutes of Health. The TV003/TV005 was licensed to three well-established manufacturers in India (and in China, Japan and Europe) and is under clinical trials.