Researchers from Singapore-MIT Alliance for Research and Technology (SMART), MIT’s research enterprise in Singapore, have found a practical way to induce a strong and broad immunity to the dengue virus based on proof-of-concept studies in mice. Dengue is a mosquito-borne viral disease with an estimated 100 million symptomatic infections every year. It is endemic in over 100 countries in the world, from the United States to Africa and wide swathes of Asia. In Singapore, over 1,700 dengue new cases were reported recently.
The study is reported in a paper titled “Sequential immunization induces strong and broad immunity against all four dengue virus serotypes” published in NPJ Vaccines. It is jointly published by SMART researchers Jue Hou, Shubham Shrivastava, Hooi Linn Loo, Lan Hiong Wong, Eng Eong Ooi, Jianzhu Chen from SMART’s Infectious Diseases (ID) and Antimicrobial Resistance (AMR) Interdisciplinary Research Groups (IRGs).
The dengue virus (DENV) consists of four antigenically distinct serotypes and there is no lasting immunity following infection with any of the DENV serotypes, meaning someone can be infected again by any of the remaining three variants of DENVs.
Today, Dengvaxia® is the only vaccine available to combat dengue. It consists of four variant dengue antigens, one for each of the four serotypes of dengue, expressed from attenuated yellow-fever virus. The current three doses of immunisation with the tetravalent vaccine induces only suboptimal protection against DENV1 and DENV2. Furthermore, in people who have not been infected by dengue, the vaccine induces a more severe dengue infection in the future. Therefore in most of the world, the vaccination is only given to those who have been previously infected.
To help overcome these issues, SMART researchers tested on mice whether sequential immunisation (or one serotype per dose) induces stronger and broader immunity against four DENV serotypes than tetravalent-formulated immunisation – and found that sequential immunisation induced significantly higher levels of virus-specific T cell responses than tetravalent immunisation. Moreover, sequential immunisation induced higher levels of neutralising antibodies to all four DENV serotypes than tetravalent vaccination.
“The principle of sequential immunisation generally aligns with the reality for individuals living in dengue endemic areas, whose immune responses may become protective after multiple heterotypic exposures,” said Professor Eng Eong Ooi, SMART AMR Principal Investigator and senior author of the study. “We were able to find a similar affect based on the use of sequential immunisation, which will pave the way for a safe and effective use of the vaccine and to combat the virus.”
Upon these promising results, the investigators will aim to test the sequential immunisation in humans in the near future.
COVID-19 may have dominated the headlines this year, but concern has steadily grown in Singapore over another public health threat – dengue fever. In fact, the insidious mosquito-borne viral disease has seen over 20,000 infections in Singapore as of July this year, surpassing the annual total from any other year except 2013. Even more worryingly, Singapore has seen weekly dengue infection numbers exceed 1,000 for seven consecutive weeks, with the week ending July 18 posting a record-breaking 1,733 infections. Elsewhere in Southeast Asia, the number of dengue infections is also exploding. In June, Malaysia reported an upward trend in dengue infections for six successive weeks and 84 deaths, while Indonesia reported over 70,000 dengue infections and 458 dengue-related deaths, the highest in Southeast Asia, with the Philippines reporting over 50,000 infections.
Globally, dengue has become endemic in over 100 countries across Africa, the Americas, the Eastern Mediterranean, Southeast Asia and the Western Pacific, with Asia representing about 70 per cent of the global burden of disease.